Chapter 4: Four-Membered Ring Systems

94

Chapter 4 Four-Membered Ring Systems Benito Alcaide Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense de Madrid, 28040-Madrid. Spain [email protected] Pedro Almendros Instituto de Química Orgánica General, CSIC, Juan de la Cierva 3, 28006-Madrid, Spain [email protected] ______________________________________________________________ 4.1

INTRODUCTION

Recently, there has been explosive growth in the research area of four-membered heterocycles, where a non-carbon atom is part of the ring, within many fields of Science, including Organic Chemistry, Inorganic Chemistry, Medicinal Chemistry, and Material Science. Condensing the vast amount of published material during the year 2008 to less than 20 pages is an extremely demanding task. A substantial portion of this material is founded on oxygen- and nitrogen-containing heterocycles, which dominate the field in terms of the number of publications. Our aim is to highlight the current state of the art in the vast area of four-membered heterocyclic chemistry. 4.2

AZETIDINES, AZETINES, AND RELATED SYSTEMS

Recent progress on the chemistry of azetidines, azetines, azetes and related systems has been reviewed in several publications <08CHEC-III1; 08CHEC-III239; 08CHEC-III623; 08CHEC-III689; 08CR3988; 08MI1; 08MI443>. A new Daphniphyllum alkaloid, calyciphylline J 1 has been isolated <08T1901>. A review on the biosynthesis and taxonomic significance of non-protein amino acids, including azetidine-2-carboxylic acid 2 has been published <08MI93>. The influence of 2-alkyl-2-carboxyazetidines (Aze) on the threedimensional structure of model tetrapeptides R2CO-2-R1Aze-L-Ala-NHMe 3 has been analyzed by molecular modeling, 1H NMR, and FT-IR studies <08JOC1704>. The synthesis and evaluation of novel azetidine lincosamides 4 have been described <08BMCL2645>. A lead benzamide, bearing both cyanopyridyl and methylazetidinyl moieties, has been identified as a potent and low molecular weight histone deacetylase (HDAC) inhibitor <08BMCL2525>. The stereoselective syntheses of cis conformationally constrained glutamate and aspartate analogues, containing an azetidine framework have been accomplished from an azetidin-3-one obtained from (S)-N-tosyl-2-phenylglycine <08T9928>. 3-Aminoazetidine linkers for the synthesis of dendrimers based on melamine have been identified using competition reactions, showing that azetidine is 40 times more reactive than the cyclic, nine-membered ring (C8H17N), and 320 times more reactive than benzylamine

c 2009 Elsevier Limited. All rights reserved. 

95

Four-Membered Ring Systems

<08TL1152>. Cycloreversion of cis- and trans-1,2,3-triphenylazetidine has been achieved by electron transfer <08OL5207>. HOOC O

H

R1

CO2H N

N

O

R2

2

1

N H

N

H

O

O

H N

Cl

R2 N

O

3

N H R1

O

HO

OH

HO

4

S

A general method has been developed for the synthesis of 1-arylsulfonylazetidines 5 through a one-pot reaction of 1-arylsulfonylaziridines with dimethylsulfoxonium methylide <08SL108>. 2-(Dichloromethylene)azetidines 6 constitute a new class of stable exocyclic enamines, which have been prepared on a multigram scale in good yields through the imination of ȕ-halo ketones, followed by Įƍ,Įƍ-dichlorination and subsequent 1,4dehydrohalogenation <08SL1394>. A sequence involving amination, bromination, and baseinduced cyclization of alkyl 2-(bromomethyl)acrylates has been used for the synthesis of alkyl 3-bromoazetidine-3-carboxylates, which are promising synthons as demonstrated by their transformation to 3-aminoazetidine-3-carboxylates <08TL6896>. A bicyclic 1,2diazetidine has been located using DFT methods on studying the formal [2ı+2ı+2ʌ] cycloaddition of quadricyclane with dimethyl azodicarboxylate <08JOC8791>. SO2R3 N + R1

R2

O SMe2

i

R1

R2 N

SO2

R1

R3

5 (68–79%)

N

R2 Cl

R1

Cl

Cl

ii

R1

Cl Cl

R1

N

R2

6 (45–62%)

Reagents: i) MW, 160 W, Al2O3, 90 oC. ii) (a) NCS, CCl4, Δ; (b) NaOMe, MeOH, Δ. A one-pot diastereoselective annulation of unmodified Baylis–Hillman adducts with N-arylphosphoramidates to afford 1,2-disubstituted azetidine-3-carbonitriles/carboxylates 7, which are the precursors of biologically versatile azetidine-3-carboxylic acids has been accomplished <08TL5652>. The cycloaddition of alkynyl ketones with N-tosylimines catalyzed by the Lewis base 4-dimethylaminopyridine formed completely substituted azetidines 8 in moderate to good yields <08JOC8491>. Studies at the PM3 level the formation of both 1,4-dihydropyridine and azetidine cycloadducts through cycloadditions of 1,4-diaryl-1-aza-1,3-butadienes with allenic esters, indicate that the transition state for the formation of [4+2] cycloadducts has lower energy, supporting the preferred formation of [4+2] cycloadducts at higher temperature and [2+2] cycloadducts at room temperature <08JOC2224>. The aza-Michael addition of diethyl N-arylphosphoramidates to chalcones affords diethyl N-aryl-N-(1,3-diaryl-3-oxopropyl)phosphoramidates, which undergo cyclization induced by anions (NCS–, PhS–) of task-specific ionic liquids to functionalized azetidines in excellent yields with high diastereoselectivity<08SL583>. A Lewis base/lanthanum aryl oxide system has been described as suitable for anti-selective Mannichtype reactions of trichloromethyl ketones, affording unique building blocks for azetidine-2carboxylic acids <08AG(E)9125>.

96

B. Alcaide and P. Almendros O

OH

EWG

O EWG

Ar1

+ (EtO)2PNHAr2

R

i Ar2

O

N

+

Ar1

n(

ii

)

)

Ar

ArC=NTs

7 (84–93%)

n(

R

N

Ts

8 (22–75%)

Reagents: i) NaH, C6H6, 60 oC. ii) DMAP, CH2Cl2, RT. An efficient approach to installing the azetidin-3-yl substituent into aromatic systems, using a nickel-mediated alkylíaryl Suzuki coupling, has been presented <08OL3259>. A three-step mechanism involving the formation and rearrangement of the intermediate 9 with an indoline-azetidine spirocyclic core structure was shown by DFT computations to account for the electrophilic cyclization of tryptophan derivatives to hexahydropyrrolo[2,3-b]indoles <08OL77>. The spirocyclic azetidine tert-butyl 1-azaspiro[3.4]oct-6-ene-1-carboxylate has been prepared from 3-choropropionitrile using ring closing metathesis as the key step <08EJO5647>. A convenient access route to monoprotected 2,6-diazaspiro[3.3]heptane and its participation in Pd-mediated amination reactions to furnish a variety of N-Boc-Nƍ-aryl-2,6diazaspiro[3.3]heptanes 10 has been documented <08OL3525>. On treatment with DAST (diethylaminosulfur trifluoride), enantiopure 2-hydroxyalkylazetidines stereospecifically rearrange into 3-fluoropyrrolidines 11 <08SL1345>. Similarly, a series of 2-(αhydroxyalkyl)azetidines by treatment with either thionyl chloride or methanesulfonyl chloride in the presence of triethylamine rearrange stereospecifically to 3-(chloro- or methanesulfonyloxy)pyrrolidines <08EJO3286>. Readily-synthesized, water-stable Pd(II) complexes of azetidine-based tridentate ligands 12 have been proven to be efficient catalysts for the Suzuki–Miyaura coupling reaction <08T7178>. The evaluation of enantiopure N(ferrocenylmethyl)azetidin-2-yl(diphenyl)methanol for catalytic asymmetric addition of organozinc reagents to aldehydes has been reported <08JOC168>. H HO2C

9

CO2H

N SeMe N CO2H

Boc

OH Ph

N N 10

Ar

Me

R N

Me

Ph i

Me

F N Me

N R

11 (45–81)%

N

NHR

12

Reagent: i) DAST, CH2Cl2, RT. Substituted β-amino acids has been prepared from the stable four-membered azetinebased heterocycle 13 <08JOC1264>. Irradiation of 2-diazo-3-oxochlorins has generated Wolff-rearranged pyrrole ring-contracted azeteoporphyrinoids <08JA15864>. A combined experimental and computational study of the conrotatory ring opening of various 3-chloro-2azetines has been carried out <08JOC5481>. The Pd(0)-catalyzed cyclization of diversely substituted N(allenylmethyl) hydrazines with aryl halides has afforded 1,2-diazetidines 14 bearing two chiral centers in high regio- and diastereoselectively (trans only) <08AG(E)4581>. A planar-chiral derivative of 4-pyrrolidinopyridine mediates the [2+2] cycloaddition of ketenes with azo compounds in a convergent manner with good enantioselectivity, thus giving the first catalytic asymmetric synthesis of aza-β-lactams 15 <08AG(E)7048>. The fragmentation of a 4-imino-1,2-oxoazetidine under acidic conditions

97

Four-Membered Ring Systems

has been described <08AG(E)947>. Nitrosobenzene-mediated CíC bond cleavage reactions and spectral observation of the oxazetidin-4-one ring system 16 has been reported <08JA12276>. R2

O R2

N

N

R1 Ph 13

N

H EtO2C

R1 N N

CO2Et

i

alkyl CO2Me Ar N N N N CO2Me EtO2C CO2Et O 15 14 R1

O

N O

Ph

16

Reagents: i) R2I, 5 mol% Pd(PPh3)4, Cs2CO3, MeCN, 80 oC. 4.3

MONOCYCLIC 2-AZETIDINONES (β-LACTAMS)

Reviews addressing recent progress on the synthesis of the β-lactam nucleus have been published <08CR3988; 08MI219>. The preparation of β-lactams by [2+2] cycloaddition of ketenes and imines has been reviewed <08T10465>. An essay on Hugo Schiff, Schiff bases, and a century of β-lactam synthesis has appeared <08AG(E)1016>. The synthesis and reactivity of silylformylation products derived from alkynes to afford α-silylmethylene βlactams has been reviewed <08EJO3039>. A review on bifunctional asymmetric catalysis, focusing on cooperative Lewis acid/base systems, for the preparation of different products including β-lactams has been published <08ACR655>. The mechanism of the keteneíimine (Staudinger) reaction in its centennial has been reviewed <08ACR925>. The mechanism of the reaction between Fischer carbene complexes and imines to produce β-lactams has been studied by a combination of computational (DFT) and experimental methodologies <08JA13892>. Densely functionalized 3-substituted 3-hydroxy-β-lactams 17 have been obtained via acyloxyallylation of azetidine-2,3-diones with 3-bromopropenyl acetate or 3bromopropenyl benzoate, in aqueous media promoted by indium under Barbier conditions <08EJO4434>. The stereochemical course of the Staudinger-like [2+2] cycloaddition of N,Ndialkylhydrazones to N-benzyl-N-(benzyloxycarbonyl)aminoketene can be efficiently controlled by the reaction temperature to afford trans- or cis-cycloadducts as the major products <08EJO2960>. The disaccharide moiety of the antibiotic mannopeptimycin ε has been synthesized as a (N-phenyl)trifluoroacetimidate donor, and its reactivity was tested in the glycoconjugation of a 4-alkylidene-β-lactam acceptor <08EJO2895>. Hybrid glycopeptide β-lactam mimetics designed to bind lectins or carbohydrate recognition domains in selectins have been prepared according to a “shape-modulating linker” design using the azideíalkyne “click” cycloaddition reaction <08OL2227>. A selection of 3-mono- and 3,3dihalogenated 1,4-diaryl substituted β-lactams has been tested as inhibitors of the serine protease porcine pancreatic elastase <08M835>. The induction of tumor cell apoptosis by a novel class of N-thiolated β-lactams with structural modifications at N-1 and C-3 of the lactam ring has been described <08MI689>. Mechanistic insights into the inhibition of prostate specific antigens by β-lactams have been reported <08MI1416>. Nitrones derived from aromatic or aliphatic aldehydes or ketones react with hexafluoropropene (HFP) or 2Hpentafluoropropene (PFP) to give the respective fluorinated isoxazolidine derivatives which after catalytic hydrogenolysis of the NíO bond under ambient pressure and temperature leads to fluorides of β-amino acids that undergo cyclization to α-trifluoromethylated β-lactams 18 <08JOC5436>. The copper-catalyzed aerobic oxidative amidation of terminal alkynes for efficient synthesis of ynamides including β-lactam 19 has been reported <08JA834>. A

98

B. Alcaide and P. Almendros

trans-β-lactam was obtained through aminocatalytic enantioselective anti-Mannich reactions of aldehydes with in situ generated N-Boc imines followed by oxidation and cyclization <08AG(E)8700>.

H

O

O

AcO HO H O

O i

N

O

N O R 17 (45–72%)

R

O

F3 C R1

X F

R2

F ii

O

F3 C

N R3

X R1 N

O

R2 R3

O

N Ph

19

18 (55–97%)

Reagents: i) 3-Bromopropenyl acetate, In, THF/NH4Cl (sat), RT. ii) H2, Pd/C, EtOH, RT, 1 atm. The synthesis of bile acid dimers linked through 1,2,3-triazole and bis-β-lactam and their in vitro have been evaluated for antifungal and antibacterial activity <08OBC3823>. Bis-β-lactam formation from bisketene-imine cycloadditions has been accomplished <08JA2386>. Cu(OAc)2 in combination with K2CO3 is an extremely effective system for promoting the homocoupling of various β-lactam acetylenes to afford C2-symmetrical bis-βlactam-1,3-diynes 20 <08EJO1575>. 4-Acetoxy-2-azetidinones reacted with organoindium reagent generated in situ from indium and 1,6-dibromo-2,4-hexadiyne in the presence of LiCl in DMF to produce 2-azetidinones 21 selectively, possessing a 1,2,4,5-hexatetraen-3-yl group at C4 <08JO5183>. A highly stereoselective synthesis of β-lactams utilizing α-chloroimines as new and powerful chiral inductors has been accomplished <08CEJ6336>. A combined experimental and theoretical study on the cycloaddition reaction between α-bromo vinylketenes and imines to afford 3-bromoalkenylazetidin-2-ones and 3-bromo-4-alkyl-5,6dihydropyridin-2-ones has been carried out <08ASC2261>. An operationally simple fourstep procedure for the solid-phase synthesis of chiral (3S,4S)-1,3,4,4-tetrasubstituted βlactams has been described <08ASC2279>. The rapid synthesis of 1,3,4,4-tetrasubstituted βlactams from methyleneaziridines using a four-component reaction has been achieved <08JOC9762>. A non-cross-linked soluble polystyrene-supported ruthenium catalyst has been used for the intramolecular carbenoid C–H insertion of α-diazoacetamides to generate cis-β-lactams <08CAJ1256>. Light from a mercury vapor high-pressure lamp has been used to induce the photolytic decomposition of α-diazo acetamides in hexane and in nonconventional media such as water or a film to afford the corresponding β-lactams <08JO5926>. Intramolecular C–H insertion of diazo-acetamides catalyzed by di-rhodium(II) complexes to generate β-lactams has been demonstrated <08TL7372>. N-Heterocyclic carbenes, electrogenerated by electrolysis of imidazolium-based room-temperature ionic liquids, are stable bases that are strong enough to deprotonate bromoamides yielding the azetidin-2-one ring via C–3/C–4 bond formation <08ASC1355>. The enantioselective synthesis of cis-4-formyl-β-lactams via chiral N-heterocyclic carbene-catalyzed kinetic resolution has been achieved <08ASC1258>.

R2 2 O

H H R1 N

i

R2 O

H H R1

R1 H H R2

N

N 20 (81–100%)

O

R O

H H OAc N

H

ii

R O

H H N

H

21 (45–63%)

99

Four-Membered Ring Systems

Reagents: i) Cu(OAc)2, K2CO3, MeCN, RT. ii) 1,6-Dibromo-2,4-hexadiyne, In, LiCl, DMF, RT. A highly stereoselective synthesis of chiral α-amino β-lactams 22 through an ynamide-Kinugasa reaction has been described <08OL3477>. N-(4-Methoxy or 4ethoxyphenyl) groups can be oxidatively removed by silica gel supported ceric ammonium nitrate (CANíSiO2) under mild conditions in solution and on column <08SL381>. The chemo- as well as regioselective participation of N-aryl imines as 4π component in azaDielsíAlder reactions with 3-butadienyl-2-azetidinones in the presence of Lewis acid catalysts resulting in novel quinoline derivatives has been described <08SL984>. Regio- and π-facial selective Lewis acid promoted Diels–Alder reactions of α-dienyl-β-lactams leading to the synthesis of diastereomerically pure 1,3,4-trisubstituted-2-azetidinones have been reported <08T6801>. A highly enantioselective synthesis of N-Boc cis-β-lactams through chiral N-heterocyclic carbene-catalyzed Staudinger reaction of arylalkylketenes with a variety of N-tert-butoxycarbonyl arylimines can be achieved <08OL277>. N-Heterocyclic carbenes have promoted the formal [2+2] cycloaddition of ketenes with N-tosyl imines to give the corresponding β-lactams in good to excellent isolated yields; chiral NHCs give β-lactams in high e.e. after crystallisation <08OBC1108>. Theoretical calculations on the transition states of the cyclization of 2S-chloropropionyl amino acid derivatives to the corresponding ȕlactams have served to explain the high stereoselectivity of the reaction, and have been the driving force to extend the procedure to the preparation of a Gly-derived 1,3,4-trisubstituted 2-azetidinone in enantiopure form <08TL215>. N-Alkyl β-lactams have been prepared by a palladium-catalyzed [2+2] carbonylative cycloaddition of allyl bromide with heteroarylidene N-alkyl-amines <08T11632>. A general method for the synthesis of 4-alkyliden-2azetidinones 23 via copper-catalyzed intramolecular CíN coupling of 3-bromobut-3enamides has been developed, with 4-exo ring closure fundamentally preferred over other modes of cyclization <08OL4037>. O O R1

N

R1 O

+

R2 O

N

O

i N

R3

R1 R2

O

N

Br Br

R3

22 (60–80%)

O

NHR2

R1

ii Br

O

N

R2

23 (70–99%)

Reagents: i) 20 mol % CuI, Cy2NMe, MeCN, RT. ii) 5 mol % CuI, Me2NCH2CO2H, THF, reflux. The asymmetric synthesis of difluoro-β-lactams using a menthyl group as a chiral auxiliary, through rhodium-catalyzed Reformatsky-type reaction has been achieved <08TL3839>. A two-step protocol for the synthesis of various functionalized gemdifluorinated β-lactams in moderate to good yields has been developed using GilmaníSpeeter and Reformatsky reactions <08EJO4277>. Decomposition of a diazo β-ketoamide derived from N-trityl serine imidazolide and N-protected acetanilides provided, instead of the expected 3-acyloxindole product, an enantiomerically pure β-lactam <08OL369>. Methyl 3(diethylamino)acrylate, generated in situ from Et2NH and methyl propiolate, on reaction with arylsulfonyl isocyanates afforded exclusively azetidine-2,4-diones in good yields <08S1747>. A synthesis of substituted 3-alkylidene-β-lactams involves a NaOH-promoted intramolecular aza-Michael addition of α-carbamoyl, α-(1-chlorovinyl) ketene-S,S-acetals

100

B. Alcaide and P. Almendros

and subsequent nucleophilic vinylic substitution reaction in alcoholic aqueous media <08T4959>. A selective synthesis of 4-alkylidene-β-lactams from azides and aryloxyacetyl chlorides via a ketenimine-participating one-pot cascade process has been achieved <08JOC3574>. A RuCl3-catalyzed protocol for the regioselective hydroamidation of amides, including 2-azetidinone, with terminal alkynes has been reported <08ASC2701>. 3Benzylazetidin-2-ones have been prepared through Negishi cross-coupling of the zinc reagent derived from N-benzyl 3-iodomethyl azetidin-2-one and aryl halides <08T3701>. A route to synthesize 1-nosyl 3,3-dichloro-β-lactams using a Staudinger reaction between N-nosyl imines and dichloroketene has been published <08JOC7837>. Optically active β-lactams have been synthesized via photochemical intramolecular γ-hydrogen abstraction from thioimides involving a highly-controlled chiral-memory effect <08CC2132>. A new one-pot approach to tetrasubstituted pyrroles 24 from β-lactams, relies on the regiocontrolled cyclization of the β-allenamine intermediates derived from the ring opening of 2-azetidinonetethered allenols <08CEJ637>. Molecular iodine catalyzes the ring expansion of 4oxoazetidine-2-carbaldehydes in the presence of tert-butyldimethyl cyanide to afford protected 5-cyano-3,4-dihydroxypyrrolidin-2-ones 25, through a novel C3–C4 bond cleavage of the β-lactam nucleus <08CC615>. Alkylamino-substituted 2-alkoxy-2-pentenoates, obtained through ring transformation of 4-(2-halo-1,1-dimethylethyl)azetidin-2-ones upon treatment with sodium methoxide in methanol, have been transformed into 5,5-dimethyl-3oxopiperidin-2-ones 26 utilizing an excess of concentrated sulfuric acid <08SL1961>. Ring opening of protected 3-aminoalkyl-substituted azetidin-2-ones with O-, N-, or S-nucleophiles led to β,βƍ-diaminocarboxylic esters, amides, and thioesters, respectively <08SL539; 08T8659>. 3-(3-Chloropropyl)-β-lactams have been transformed selectively into transmethyl 1-alkyl-2-arylpiperidine-3-carboxylates upon treatment with hydrogen chloride in methanol then triethylamine in dichloromethane <08T4575>. An efficient synthesis of (3S,4R)-4-benzylamino-3-methoxypiperidine, a useful intermediate for the chiral synthesis of important drug molecule Cisapride and its analogs, from enantiopure 4-formylazetidin-2-one has been described <08T7191>. An approach for the synthesis of hydroxylated 2aminocyclohexanecarboxylic acid stereoisomers from 1,4-cyclohexadiene by the reductive opening of appropriate epoxide intermediates derived from the corresponding bicyclic βlactams has been developed <08T5036>. A β-lactam-based strategy allows the introduction of a nitrogen atom into the carbocycle of an aminocyclopentenecarboxylic ester using lipolase <08TL340>. A solvent-free, vapour-assisted method, for the synthesis of carbocyclic cis β-amino acid enantiomers through the Candida antarctica lipase B-catalysed enantioselective hydrolysis of β-lactams has been developed on a preparative scale <08TA1005>. Fluorine-activated β-lactams are acyl donors to N-nucleophiles in the presence of Burkholderia cepacia lipase <08TA1857>. A total synthesis of (í)-kainic acid starting from a commercially available 2-azetidinone has been described <08OL1711>. The synthesis of the biological relevant N-Boc-(2R,3R,8R,9R,4E,6E)-3-amino-9-methoxy-2,6,8-trimethyl10-phenyldecadenoic acid taking advantage of the base-promoted ring opening of a β-lactam has been completed <08JOC5015>. 4-Aryl-1-(2-chloroethyl)azetidin-2-ones have been transformed into novel 1-(1-aryl-3-hydroxypropyl)aziridines upon treatment with LiAlH4 <08OBC1190>. A PtCl2-catalyzed cycloisomerization of N-(2-alkynylphenyl) β-lactams to form benzene-fused pyrrolizinones selectively has been developed <08AG(E)346>. The Aucatalyzed synthesis of 5,6-dihydro-8H-indolizin-7-ones from N-(pent-2-en-4-ynyl)-β-lactams has been described <08OL5187>. An efficient synthesis of hydroxy-substituted cispentacin derivatives starts from a bicyclic β-lactam <08EJO3724>. The one-pot reaction of β-lactam carbenes with 1-naphthyl or 5-quinolyl isonitriles followed by treatment with aqueous

101

Four-Membered Ring Systems

hydrochloride produced benzo[h]-δ-carboline-2,4-diones or pyrido[3,2-h]-δ-carboline-2,4diones, respectively, in moderate yields <08S2883>. R2 OMe

O

N

R2

R3 R

i

CO2Me

R1O

R1O

R3 N 1 R 24 (49–68%)

O

Me

1

N

O

OTBS

O

CN

O

ii O

R2

N R2

N R 26

25 (46–89%)

Reagents: i) MeONa, MeOH, reflux. ii) TBSCN, 10 mol% I2, MeCN, RT. FUSED AND SPIROCYCLIC β-LACTAMS

4.4

The chemistry of cephalosporins and penicillins has been reviewed <08CHEC-III111; 08CHEC-III173>. The antagonistic interactions between the flavonoids hesperetin and naringenin and β-lactam antibiotics against Staphylococcus aureus have been described <08MI145>. The quantitative retention-activity relationships (QRAR) model of β-lactam antibiotics has been studied <08MI2>. The increased antibacterial activity of β-lactam heterodimers in comparison with their monomeric components has been reported <08JAN595>. The reaction of Schiff bases derived from 3-cyano-2,4-diamino thiophene with chloroacetyl chloride afforded spiro-β-lactams <08PS1679>. The heterocyclizative crosscoupling between 2-azetidinone-tethered allenols and α-allenic acetates gave β-lactam– dihydrofuran hybrids 27 in good yields <08CAJ1140>. New 3-heterocycle substituted 1,3thiazolidine-derived 4-spiro-β-lactams with a relative trans-configuration have been stereoselectively synthesised by means of a Staudinger ketene–imine reaction <08TA554>. Oxacyclopropane formation gives the highly strained oxiranyl-β-lactam 28, possessing a spirocyclic structure by treatment of a 3-[bromo(nitro)methyl] 3-hydroxy-β-lactam with bases <08OBC1635>. A novel Pd(II)- catalyzed C෥H lactamization reaction, including the formation of spiro-β-lactams has been achieved <08JA14058>.

R2 OH

O

N

OAc

O O

+ Ar

Me

i

R1

O

O

H O

H

O O

O2N R1

N

O

R2

27 (47–75%)

Reagents: i) 5 mol % PdCl2, DMF, 0 oC.

O

Me Ar

O

N 28

PMP



Synthetic studies and biosynthetic speculation inspired by an unexpected reaction on the marine alkaloid chartelline C 29 which has a spirocyclic β-lactam unit, have been described <08CC3121>. The isolation, structural elucidation and biological characterization of phyllostictine A, a new phytotoxic oxatricyclic β-lactam 30, produced in liquid culture by P. cirsii, have been described <08T1612>. Various glutaryl acylase mutants have been evaluated to improve the hydrolysis of cephalosporin C 31 in the absence of hydrogen peroxide <08ASC343>. A thermal decarbonylation of penam β-lactams has been developed <08JOC3024>. Mechanisms for the hydrolysis of nitrocefin and penicillin G have been proposed <08JA14207; 08JA15842>. β-Lactams have been examined as selective chemical probes for the in vivo labeling of bacterial enzymes involved in cell wall biosynthesis,

102

B. Alcaide and P. Almendros

antibiotic resistance, and virulence <08JA13400>. A study of the biosensing process involving fluorophore-labeled β-lactamase as a biosensor for β-lactam antibiotics has been carried out <08JA6351>. The resolution of racemic 2-chlorophenyl glycine with immobilized penicillin G acylase has been achieved <08TA2363>. O N Br

O

Cl N N H

N 29

Br

O

N

OH

MeO HO 30

Me Me

R1HN O

R2

S N

CH2R3 CO2H

R1 = (R) HO2C(NH2)CH(CH2)3CO R2 = H, R3 = OAc

31  An approach for synthesizing a series of 2-sulfide carbapenems has been developed using two successive Cu(I)-catalyzed cross-couplings in a single pot <08OL2737>. Two different stereocontrolled accesses to new 4-hydroxypipecolic acid analogues 32 with a bicyclic β-lactam structure have been developed by using intramolecular reductive amination or allenic hydroamination reactions in 2-azetidinone-tethered azides <08JOC1635>. A variety of β-lactams bearing protected polar substituents was generated from chlorosulfonyl isocyanate (CSI)-derived building blocks <08OL5317>. 1-Allyl-substituted 4-(2-bromo-1,1dimethylethyl)azetidin-2-ones have been transformed into bicyclic β-lactams through radical cyclization by means of n-tributyltin hydride and AIBN in toluene with excellent diastereocontrol <08JOC1422>. It has been reported that chlorosulfonyl isocyanate addition to (í)- and (+)-apopinene furnished monoterpene-fused β-lactams in highly regio- and stereospecific reactions <08TA2296>. A convenient approach to novel selenium-β-lactams such as 3-selena-1-dethiacephems 33 involved a regioselective iodocyclization <08OL3319>. The chemoselective cycloetherification reaction of enallenols under iron-catalyzed conditions resulted in the preparation of bicyclic β-lactams 34 <08CEJ7756>. The stereoselective synthesis of carbapenams via Kinugasa reaction involved cyclic nitrones derived from malic and tartaric acid <08JOC7402>. A three-step procedure involving imine formation/Staudinger reaction/PausoníKhand cycloaddition enabled the preparation of fusedtricyclic azetidinones from the reaction of N-tosyl-N-allyl ketene with complexed acetals derived from propargylic aldehydes <08JOC8469>. A CeCl3·7H2O/NaI-promoted synthetic protocol for strained tricyclic β-lactams 35 has been developed from hydrazines <08TL5553>. The reaction of 3-arylisoxazoles with LDA in THF at 0 °C afforded syn-2,6diaryl-3,7-diazatricyclo[4.2.0.02,5]octan-4,8-diones (bis-azetidinones), via stereoselective dimerization of an azetidinone anion intermediate <08T11198>. A ring closing metathesis approach to N1–C3 bridged macrocyclic β-lactams has been developed <08T9592>. The synthesis and structural characterization of β-lactam condensed 3-thiaquinolines have been achieved <08T1002>. α,β-Unsaturated aldehydes, including 3-alkyl derivatives, undergo Nheterocyclic carbene (NHC)-catalyzed annulations with N-sulfonyl ketimines to provide bicyclic β-lactams 36 with outstanding diastereo- and enantioselectivity <08JA418>.

103

Four-Membered Ring Systems R3 R2 N H O

TBSO

OH Me H N 32

R1

H H

R1 O

N

Se N

33

R2

R2

O

I H O

H N 34

R1

R2 Ar1 O R1 N N O Ar2 35

Ar1

S

R H O

Ar2 N 36

SO2Ar



 4.5 OXETANES, DIOXETANES, OXETANEDIONES AND 2-OXETANONES (βLACTONES) The chemistry of oxetanes, dioxetanes, and oxetenes has been reviewed <08CHECIII321; 08CHEC-III365; 08CHEC-III775>. Reviews on recent progress on four-membered rings with two oxygen atoms <08CHEC-III775> the chemistry of 1,2-dioxetanes <08MI351>, carbonyl-olefination with ynolates via oxetene intermediates <08SL2231>, cobalt-chemistry including oxetanes and 2-oxetanones <08S3537> have appeared. Progress in the use of second-generation taxoids for tumor-targeting chemotherapy has been reviewed <08ACR108>. An account of NMR and synthetic studies establishing the T-taxol conformation as the bioactive tubulin-binding conformation has been published <08JOC3975>. Vibrational circular dichroism analysis reveals a conformational change of the baccatin III ring of paclitaxel 37 <08JOC2367>. Paclitaxel-polylactide nanoconjugates have been prepared by the site-specific polymerization of lactide mediated by a paclitaxelmetal complex followed by nanoprecipitation <08AG(E)4830>. A method has been developed for the methylation of the C3ƍ amide of taxol C and paclitaxel <08JOC4705>. Chemo-enzymatic synthesis of ester-linked taxol–oligosaccharide conjugates gives potential prodrugs <08TL601>. Danishefsky’s taxol CD ring key intermediate has been stereoselectivelly synthesized in 15 steps and 11.4% overall yield from a readily available starting material <08JOC6033>. The design, synthesis, and characterization of triazine dendrimers derivatized with the anticancer agent paclitaxel have been described <08OL201>. The synthesis of new D-seco-C-nor-taxane derivatives in which the D-ring has been deleted and the C-ring has been transformed into a new pentatomic ring, started from baccatin III derivatives <08JOC8893>. There is rotamer-dependent chemiluminescence in the intramolecular charge-transfer-induced decomposition of bicyclic dioxetanes 38 bearing a hydroxyaryl group <08TL5372>. There is a marked difference in singlet-chemiexcitation efficiency between syn-anti isomers of spiro[1,2-dioxetane-3,1ƍ-dihydroisobenzofuran] for intramolecular charge-transfer-induced decomposition <08TL6145>. The solvent-promoted chemiluminescent decomposition of a bicyclic dioxetane bearing a 4-(benzothiazol-2-yl)-3hydroxyphenyl moiety has been reported <08TL4170>. Spirocyclic oxetanes are analogues of morpholine and also topological siblings of their carbonyl counterparts <08AG(E)4512>. A ruthenium-catalyzed synthesis of primary amines directly from alcohols, including aminooxetanes, and ammonia has been achieved under mild conditions <08AG(E)8661>. The bicyclic oxetane 39 has been prepared during the total synthesis of the halogenated marine natural product (+)-obtusenyne <08CEJ2867>.

104

B. Alcaide and P. Almendros

AcO

O

O O NH

Ph

O OH

O

OH O H OAc PhOCO

O

Ph OH

R

HO

Cl

H

t-Bu

O

N

O H

38

OTBDPS

39

37

Evidence that the (6–4) photolyase mechanism can proceed through an oxetane intermediate has been found <08JA12618>. The synthesis of epi-oxetin 40, an oxetanecontaining β-amino acid, via a serine-derived 2-methyleneoxetane has been accomplished <08JOC517>. The synthesis of tetrameric and hexameric carbopeptoids, such as the oxetane hexamer 41, derived from L-ribo 4-(aminomethyl)-oxetan-2-carboxylic acid has been achieved <08TA976>. Investigations into the secondary structural preferences of homooligomers of a new class of sugar amino acids, δ-2,4-cis-oxetane amino acids, have been reported <08TA984>. Mechanistic studies of the copolymerization reaction of oxetane and carbon dioxide to provide aliphatic polycarbonates catalyzed by (salen)CrX complexes have been carried out <08JA6524>. (í)-Minlactone has been synthesized using oxetane as a building block <08JOC8104>. The syntheses of haterumalides NA and NC have been accomplished via the macrocyclization of a chlorovinylidene chromium carbenoid, the preparation of which began with the ring-opening of oxetane, onto a pendant aldehyde <08JA12228>. The regioselective ring opening of 2-aryl oxetanes and 2-aryl azetidines with phenols, including catechol, has been achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts <08JOC8998>. The reductive opening of oxetanes by Cp2TiCl has been investigated by a combined synthetic and computational study <08T11839>. Ȧ-Trichloroalkyl phenyl ethers have been synthesized through a tandem reaction of benzyne with cyclic ethers, including oxetane <08TL3063>. The carbonylative polymerization of oxetanes initiated by acetyl cobalt complexes has been reported <08CAJ710>. Treatment of fused oxetanes bearing a 2-methoxyphenyl moiety with Lewis acids leads to the formation of spirocyclic dihydrobenzofurans through intramolecular attack of an oxygen atom of the proximal phenolic methyl ether <08SL25>. O HO

OH NH2

R2

O OBn

i

TrHN

iii

ii

O

O O N H

O OBn

TrHN

iv

vi–x O

N H

O OBn

O

O

N H

CO2H

O 40 (2% overall yield from L-serine)

O O

H2N

OBn

O N H

O OBn

O N H

O

CO2R1

OBn

41

Reagents: i) TMSCl, Et3N, MeOH, TrCl, RT. ii) BOP, Et3N, CH2Cl2, RT. iii) Cp2TiMe2, toluene, 80 oC. iv) DMDO, CH2Cl2, RT. v) DIBAL-H, toluene, –78 oC. vi) Ac2O, pyridine, RT. vii) (a) TFA, RT; (b) Et3N, Boc2O, RT. viii) NaOMe, MeOH, RT. ix) RuCl3, NaIO4, CCl4, MeCN, H2O. x) TFA, CH2Cl2, RT. 2-Nitrophenyl isocyanide is a convertible isocyanide as demonstrated by its feasibility and applicability in an efficient synthesis of the fused γ-lactam β-lactone bicycle of

105

Four-Membered Ring Systems

proteasome inhibitor omuralide 42 <08JOC4198>. An alkylidene carbene 1,5-CH insertion was used as a key step in an enantioselective total syntheses of omuralide, its C7-epimer, and (+)-lactacystin <08JOC2041>. The synthesis of (–)-salinosporamide A 43 illustrated the synthetic utility of the In(OTf)3-catalyzed cyclization of nitrogen- and oxygen-tethered acetylenic malonic esters <08AG(E)6244>. A concise and straightforward total synthesis of (±)-salinosporamide A, based on a biosynthesis model has been accomplished <08OBC2782>. The total synthesis of salinosporamide A has been achieved through enzymatic desymmetrization, diastereoselective aldol reaction, intramolecular aldol reaction, and intramolecular Reformatsky-type reaction followed by 1,4-reduction, as key reactions <08OL4239>. The engineered biosynthesis of antiprotealide and other unnatural salinosporamide proteasome inhibitors has been reported <08JA7822>. The mutasynthesis of fluorosalinosporamide, a potent and reversible inhibitor of proteasome, has been described <08AG(E)3936 >. The synthesis of (±)-vibralactone, (–)-vibralactone 44, and vibralactone C have been accomplished <08OL1401; 08JOC8049>. The synthesis of 2,3- and 3,4methanoamino acid equivalents with stereochemical diversity and their conversion into the tripeptide proteasome inhibitor belactosin A 45 and its highly potent cis-cyclopropane stereoisomer was achieved <08OL3571>. A concise stereoselective total synthesis of (í)tetrahydrolipstatin used an Oppolzer’s sultam-directed aldol reaction as the key step <08TL327>. A diastereo and enantioselective synthesis of natural and unnatural nocardiolactone utilised a proline-catalyzed crossed-aldol reaction as the key step <08T5861>. O

HO

O Cl

NH Me

NH Me

OH

O

H OH

O

O 42

O

H O

O 43

O 44

O

O

N H

H N HO2C

NH2 O

45

Stereoselective aldol reaction of a homochiral iron octanoyl complex, followed by tandem oxidative decomplexation–cyclisation facilitated the asymmetric syntheses of tetrahydrolipstatin and valilactone <08TA2620>. Spiro β-lactone-based proteasome inhibitors have been discovered in the context of an asymmetric catalytic total synthesis of the natural product (+)-lactacystin <08JA14981>. A chemical proteomic strategy was applied directly to bacterial proteomes, and β-lactones were identified as important natural product derivatives with a high affinity to various enzyme classes <08AG(E)4600>. A multidisciplinary chemical proteomic strategy has been applied and functionalized β-lactones have been identified as potent, cell permeable inhibitors for specific and selective targeting of the key virulence regulator complex ClpP in Staphylococcus aureus <08JA14400>. A strategy taking advantage of the cooperative action of aprotic contact ion pair catalysis and Lewis acid catalysis has been used for the catalytic asymmetric selective synthesis of transconfigured 3,4-disubstituted β-lactones <08AG(E)5461>. The asymmetric dimerization of disubstituted ketenes catalyzed by N-heterocyclic carbenes afforded β-lactones 46 <08ASC2715>. The formal cycloaddition of disubstituted ketenes with 2-oxoaldehydes catalyzed by chiral N-heterocyclic carbenes afforded β-lactones 47 with α-quaternary βtertiary stereocenters <08JOC8101>. Optically active γ-allenoic acids have been synthesized from β-lactones <08CEJ9659>. The one-pot synthesis of piperid-4-ones 48 has been achieved through TiCl4-promoted diketene addition to tosyl imines, followed by reaction with aldehydes <08OL2877>. Studies leading to the development of a cascade sequence that generates as many as two CíC bonds, one CíO bond, and three new stereocenters providing

106

B. Alcaide and P. Almendros

substituted tetrahydrofurans from keto β-lactones has been described <08AG(E)5026; 08JOC9545>. The synthesis of N-Boc-Į-halomethyl-Į-alkylglycines that involves cyclization of N-Boc-Į-alkylserines to the corresponding β-lactones under Mitsunobu reaction conditions, followed by ring opening with anhydrous MgX2 has been described <08TL6445>. A computational study of the dyotropic rearrangement of α-lactones to β-lactones has been performed <08OBC66>. The selective formation of a hydroxy pyroglutamate has been achieved via methanolysis of a bicyclic β-lactone <08SL2244>. Dyotropic processes involving unprecedented 1,2-acyl migrations provided access to novel spirocyclic, bridged keto-γ-lactones from a series of fused, tricyclic-β-lactones <08JA10478>. Using diketene as a basic reagent, a one-pot, pseudo-five-component reaction for the synthesis of highly substituted bisfuramides has been described <08S3742>. The one-pot synthesis of pyrrolo[2,1-a]isoquinoline-1-carboxamides via a four-component reaction involved diketene <08S429>. The synthesis of highly functionalized pyrrole derivatives via a four-component reaction of two primary amines and diketene in the presence of nitrostyrene has been accomplished <08S725>. Sulfonamides and 1,3-oxazine-2,4-diones result from arylsulfonyl isocyanates and diketene <08S2074>. The synthesis from diketene of both hydrazinesubstituted enaminones and 4,5-dihydro-1H-pyrrol-3-carboxamides has also been illustrated <08S3295; 08TL351>. The C1–C8 subunit of biselide E has beeen synthesized starting from a β-lactone <08SL2583>. O C Ar

O C

R i R

R

Ar

Ar O

O

Ar1

HO

Ar1 H ii R

COAr2

R O

N

O

46 (61–74%)

47 (73–99%)

up to 97% ee

up to 99% ee

R1

Ts + O

iii O

MeO2C R2

N Ts

R1

48 (48–98%)

Reagents: i) 10 mol% NHC, THF, RT. ii) Ar2COCHO, 10 mol% NHC, THF, RT. iii) (a) TiCl4, CH2Cl2, –78 oC, them MeOH; (b) R2CHO, RT; (c) K2CO3, DMF. The ring-opening polymerization (ROP) of racemic β-butyrolactone catalyzed by chromium(III) complexes resulted in poly(hydroxybutyrate) with high molecular weight and with isotacticities of 60–70 % <08AG(E)3458>, while the ROP promoted by bis(guanidinate) alkoxide complexes of lanthanides formed syndiotactic poly(hydroxybutyrate) through a chain-end control mechanism <08CEJ5440>. β-Lactones with fluorinated side-chains have been polymerized to form a series of new poly(β-hydroxyalkanoate)s, and their properties were examined with respect to their hydrocarbon analogs <08T6973>. 4.6

THIETANES, β-SULTAMS, AND RELATED SYSTEMS

Recent progress on the chemistry of thietanes, thietes, and four-membered rings with a heteroatom and one sulfur atom has been reviewed in several contributions <08CHECIII389; 08CHEC-III429; 08CHEC-III713; 08CHEC-III795; 08CHEC-III811; 08MI431>. The Newman-Kwart OĺS rearrangement of O-aryl thiocarbamates, including the preparation of thietanes has been reviewed <08S661>. Various 2-alkylidenethietanes 49 have been synthesized by intramolecular nucleophilic substitution reactions at an sp2 carbon of vinyl halides with thiolates <08TL4125>. Installing hydroxymethyl substitution at C4 through vinylation and hydroborationíoxidation reactions of the C4 bis-hydroxymethyl derivative of a D-glucose based substrate, and inserting the heteroatom thereafter permitted the formation

107

Four-Membered Ring Systems

of spirocyclic nucleosides 50 <08JOC4305>. A theoretical analysis of the oxidative coupling of two metal-coordinated disulfide species to an S42– rectangle provided the opportunity for reexamination of a number of compounds hitherto considered to be disulfide complexes <08AG(E)2864>. Treatment of α-dithiolactones with ethoxycarbonylformonitrile oxide resulted in the formation of 1,2-dithietan-3-ones 51, which can be oxidized to give 4,4-ditert-butyl-1,2-dithietan-3-one 1-oxides 52 <08TL36> O R2

R2

R1

S

i R1

Br

S

R2 R2

S

O

R

Uracil

R RO

49 (30–94%)

OH 50

O N

S +

R S

ii

R

R S S

iii

O CCO2Et 51 (80–82%)

R

S S

O

O 52 (76–78%)

Reagents: i) K2CO3, MeOH, N,N-dimethylimidazolidinone, 120 oC. ii) THF, RT. iii) mCPBA, CH2Cl2, RT. 3-Aryl-3-hydroxy-1-methylazetidine-2-thiones 53 react with HCl in DMSO to give 3methyl-5-aryloxazole-2-thiones through an oxidative rearrangement <08OL4975>. NBenzoyl-β-sultam 54 undergoes general base-catalyzed hydrolysis by amines in preference to aminolysis <08JOC4504>. β-Hydroxysulfinic acids and allylsulfonic acids have been accessed by chemoselective reduction of β-sultones 55 bearing a β-trichloromethyl substituent <08SL1505>. The preparation of sulfilimines from the corresponding sulfoxides using the Burgess reagent has been reported to involve the four-membered heterocycle 56 <08TL4256>. OH

R

R S

N 53

4.7

Me

Ph O S N O O 54

O S O O 55

CCl3

O S Ar O S N 1 R O 56

SILICON AND PHOSPHORUS HETEROCYCLES. MISCELLANEOUS

Recent progress on the chemistry of four-membered heterocyclic rings containing silicon, phosphorous, selenium, tellurium, arsenic, antimony, bismuth, germanium, tin, lead, or boron has been reviewed in several contributions <08CHEC-III463; 08CHEC-III479; 08CHEC-III513; 08CHEC-III555; 08CHEC-III853; 08CHEC-III875; 08CHEC-III907; 08CHEC-III973>. An overview on nickel-catalyzed transformations with trialkylboranes and silacyclobutanes has appeared <08CC3234>. The aromaticity and antiaromaticity of fourmembered P-heterocycles have been reviewed <08COR83>. Donor-free four-membered cyclic silenes, 1,2-disilacyclobut-2-enes 57, were produced from reaction of disilenides with vinylbromides <08CEJ7119> Treatment of silacyclobutanes with enones under palladium catalysis resulted in formal cycloaddition to yield the corresponding eight-membered ring <08OL2199>. 6-Oxa-2-silabicyclo[2.2.0]hexanes 58 were obtained via Paternò–Büchi reaction of acyl(allyl)silanes <08CC5833>. [2+2] Cycloaddition reactions of P2 with alkenes to give 3,4-dihydro-1,2-diphosphetes 59 have been predicted to proceed via concerted paths <08TL3578>. Calculations on 2,4-diborata-1,3-diphosphoniocyclobutane-1,3-diyls have been carried out <08AG(E)155>. Oligomers of 1,3-diphosphacyclobutane-2,4-diyl units have been reported <08AG(E)6418>. The synthetic utility of Lawesson’s reagent has been documented

108

B. Alcaide and P. Almendros

<08AG(E)10114; 08SL463; 08OL1417>. A selenium-based hexameric macrocycle containing four-membered phosphaheterocycles has been prepared <08AG(E)1111>. The synthesis and reactivity of several phosphaheterocycles having metallic atoms have been reported <08AG(E)4584; 08CC1747; 08CC4822; 08CC5547>. 2-Thia-, 2-selena-, and 2tellura-1,3,4-trisilabicyclo[1.1.0]butanes have been prepared <08JA2758>. The synthesis of 1,3-diselenetanes 60 has been achieved <08TL974>. Various azaheterocycles bearing metallic elements have been characterized <08AG(E)603; 08AG(E)5799; 08AG(E)7493; 08CC5206; 08CC6597; 08CEJ10430; 08JA8904; 08OL1267; 08TL7135>. The rhodiumcatalyzed oxygenation of 1,5-cyclooctadiene to 4-cyclooctenone with molecular oxygen proceeds via the 2-rhodaoxetane 61 <08AG(E)2502>. R1 O Si R1 Si R1 R2 57

4.8

R

P P Si

O 58

R2

Se R1

59

R

Se 60

R

O RhLn 61

REFERENCES

08ACR108 08ACR655 08ACR925 08AG(E)155 08AG(E)346 08AG(E)603 08AG(E)947 08AG(E)1016 08AG(E)1111 08AG(E)2502 08AG(E)2864 08AG(E)3458 08AG(E)3936 08AG(E)4512 08AG(E)4581 08AG(E)4584 08AG(E)4600 08AG(E)4830 08AG(E)5026 08AG(E)5461 08AG(E)5799 08AG(E)6418 08AG(E)7048 08AG(E)7493 08AG(E)8661 08AG(E)8700

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Four-Membered Ring Systems 08OL4975 08OL5187 08OL5207 08OL5317 08PS1679 08S429 08S661 08S725 08S1747 08S2074 08S2883 08S3295 08S3537 08S3742 08SL25 08SL108 08SL381 08SL463 08SL539 08SL583 08SL984 08SL1345 08SL1394 08SL1505 08SL1961 08SL2231 08SL2244 08SL2583 08T1002 08T1612 08T1901 08T3701 08T4575 08T4959 08T5036 08T5861 08T6801 08T6973 08T7178 08T7191 08T8659 08T9592 08T9928 08T10465 08T11198 08T11632 08T11839 08TA554

113

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