Insertions of silylated carbenoids into vinylzirconocene chlorides. A convergent route to silyl-substituted allylzirconium reagents

TETRAHEDRON LE'Iq'ERS Pergamon

Tetrahedron Letters 40 (1999) 9353-9357

Insertions of silylated carbenoids into vinylzirconocene chlorides. A convergent route to silyl-substituted allylzirconium reagents A l e x a n d e r N. Kasatkin and Richard J. Whitby * Department of Chemistry, Southampton Universi~. , Southampton, Hants S017 1BJ, UK Received 6 September 1999; accepted 19 October 1999

Abstract A convergent route to allylzirconocene reagents by insertion of silyl-substituted carbenoids LiCR(SiMe3)(CI) into vinylzirconocene chlorides is reported. The product silylated allylzirconocenes react with aldehydes and ketones with high anti-selectivity to afford vinyl- (R=H) or allyl- (R=Me, Pr) silanes which may be converted into 4,5-trans-disubstitituted y-lactones and stereodefined dienes. © 1999 Elsevier Science Ltd. All rights reserved. Keywords: zirconium; silicon; carbenoids; dienes; lactones; allylmetallic.

Allylmetallic species are important intermediates in organic synthesis.l The possibility of controlling regio- and stereochemistry when using allylmetallic reagents has prompted the investigation of many metal systems, and those of the group IV transition metals have proven useful.l The normal route to allyl organometallics is from the allyl halide by oxidative addition reaction, or by transmetallation from a species so formed. The use of low valent metal complexes Cp2Zr(1-butene) and (iprO)2Ti(propene) allows allyl alcohol derivatives to be used as precursors. 2 Hydrozirconation of allenes is another route to allylzirconocene reagents. 3 A particularly attractive, but little investigated, convergent route to allyl organometallics 3 is the insertion of a saturated metal carbenoid 1 into a vinyl-metal bond (Eq. 1). The insertion of LiCH2C1, LiCHC12 and LiCH(CI)SiMe3 into vinyl boronates, 4 LiCH(C1)SiMe3 into (E)-l-octenylzirconocene chloride, 5 LiCH(C1)SiMe2Ph into (E)-1-nonenyl(diisobutyl)aluminium,6 and ICH2ZnI into vinyl copper species 7 are the only examples of which we are aware. The most likely mechanism for the homologations is via a 1,2-rearrangement of an intermediate metallate complex 2 (Eq. 1). 8 We have shown that the insertion of lithium carbenoids into the carbon-zirconium bonds of zirconacycles, and organozirconocene chlorides is an exceptionally fast and efficient process. 9

* Corresponding author. Tel: 023 80592777; fax: 023 80593781; e-mail: rjwl @soton.ac.uk 0040-4039/99/$ - see front matter O 1999 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(99)01982-6

9354

R1R ~ 2

X

M

.

R

- LiX

, 2 R

R ~ I ~.~ R R 4

"

(l)

3

Hydrozirconation 1° of 1-octyne to afford (E)-octenylzirconocene chloride (4a) followed by addition of LiCH(C1)SiMe3 (5) 11 gave the allylzirconocene 6a (Scheme 1). 5 NMR studies indicate that in 6a the zirconium is on the same carbon as the trimethylsilyl group, although some q3-character to the co-ordination is likely. 12 Hydrolysis gave a 73% yield of an 89:11 mixture of the allylsilane 7a (1:1, E:Z) and the vinylsilane 8a (only E-isomer) (Scheme 1). 13 Work-up of the allylzirconocene species 6a with benzaldehyde gave a mixture of three products (9a-lla), with the former strongly favoured (Table 1, entry 1). The (E)-vinylsilane 9a was obtained with >97:3 anti:syn diastereocontrol. The (Z)vinylsilane 10a also seemed to be formed with high anti-selectivity although the small amounts formed made measurement impossible. The minor product l l a containing a 13-hydroxysilane functionality was easily removed by acid treatment 14 (to give the diene 12) followed by chromatography. With the addition of BF3 .Et20 to the aldehyde addition reaction 9a became the almost exclusive product (entry 2). 15 The overall transformation comprises a three component coupling with excellent regio- and stereocontrol. (~l RIC=CH

i.

MeaSi~ Li

ii. H C I

• CP2Zr.,,~'~ R 1

5

,.

~rCp2CI Me3S.K..,~...~.~ R 1

a R 1=n-Cell13 b RI=(CH2)2OBn c R 1=SiMs3

"

v, vi, vii 9b

, M e 3 S I " ' ~ " ~ - ~ R 1 + Me3S"~r~,.~...,.-"~R1 7

6

4

Pr"~O"'~O

iii

R~ R

13, 42%

iv, iii. I R

H

H

viii

,, 11 only

SiMe3 +

H~I:~I

8

R1

R2

9

12

Scheme 1. (i) Cp2ZrHCI, THE 20°C, 1 h; (ii) 5, -78 to -40°C over 1 h; (iii) NaHCO3aq. (iv) 1.3 equiv. R2CHO/(BFa.Et20), -78 to 20°C, then 20°C, 18 h; (v) mCPBA, CH2C12, 20°C, 18 h; (vi) MeOH, BF3 .Et20, 20°C, 18 h; (vii) BF3 .Et20 (20 tool%), mCPBA, CH2C12, 20°C, 3 h; (viii) 2 M HClaq., THE 20°C, 18 h Table 1 Reaction of allylzirconocenes 6 with aldehydes (Scheme 1) R2R3CO Entry

R1

R2

R3

1 2 3 4

n-Call13 n-CsHla n-Cell13 n-CeHla

Ph Ph Pr Pr

H H H H

5 6 7 8 9 10

n-Cell13 n-C6H13 -(CH2)2OBn -(CH2)2OBn n-Cell13

SiMe3

iPr MeCH=CH Ph Ph Ph

Ph

H H H H Me

H

After acid treatment

RaUob

Conditions BFa.Et20 BFa.Et20 BF3.Et20 BF3.Et20 BF3.Et20

Product

Yield %¢1

9 a : 10

a • b b

55 57 65 55

89:3 >95 : <5 64:7 83:4

: : : :

8 0 29 13

48

97 : 3

45 46

90 : 10 95 : 5

c d • • f

58 53 50 52 55 71

79:3 : 71 : 6 : 80:0 : >95 : <5 : 72• : 0 : 72 : 28 c

18 23 20 0 23

45 40

97 : 3 92 : 8

40

100•:

g

Yield,%a

9 c : 10 : 11

0

a Isolated combined yield of 9, 10, and 11 based on the starting acetylene, b Determined by 1H NMR analysis. ¢ >97:3 antt..syn d Isolated combined yield of 9 and 10 based on the starting acetylene. Ratio of 9 : 10 by NMR • 93 : 7 anti: syn. f ant/-Isomer only.

9355

The reaction of 6a with aliphatic and et, 13-unsaturated aldehydes also worked well (Table 1, entries 3-6), with excellent diastereocontrol. The stereochemistry of 9b was proven by its conversion into the 4,5trans-y-lactone 13 and comparison of NMR data with similar known compounds. 16 Hydrozirconation of 1-benzyloxy-3-butyne followed by the insertion of 5 gave the functionalised allylzirconocene 6b which afforded only the allylsilane 7b (77%, 44:56, E:Z) on hydrolysis. Reaction of 6b with benzaldehyde gave the products 9e and l l e with the notable absence of the (Z)-vinylsilane 10e (Table 1, entry 7). In the presence of BF3.Et20 there was excellent regio- and stereocontrol in favour of the (E)-anti isomer 9e (entry 8). 17 The allylzirconocene 6a also proved reactive towards acetophenone to give a mixture of vinyl- and allylsilane products 9f and l l f (entry 9). The absence of the (Z)-alkene 10f, and the lower anti-selectivity in the formation of 9f are notable. After treatment with acid to aid removal of l l f the vinylsilane 9f was isolated with a 93:7 ratio of anti:syn diastereoisomers.18 Hydrozirconation of trimethylsilylacetylene to afford 4c followed by insertion of 5 gave the allylzirconocene 6c (Scheme 1). 19 Addition of benzaldehyde gave a mixture of (E)- and (Z)-vinylsilanes 9g and 10g, both exclusively the anti-diastereoisomers (Table 1, entry 10). The relative configuration and double bond geometries of 9g and 10g were proven by their conversion to the (1Z,3E)- and (1Z,3Z)-l-phenyl-4-trimethylsilylbutadienes, respectively, on treatment with potassium hydride. 14 Insertion of alkyl-substituted carbenoids LiC(C1)(R)SiMe32° 14 into vinylzirconocenes was examined next. The reaction of 14a and b with (E)-1-octenylzirconocene chloride (4a) afforded the allylzirconocenes 15 (Scheme 2). Hydrolysis exclusively gave the allylsilanes 16 as the (E)-isomers. Treatment of 15 with benzaldehyde gave the allylsilanes 17 with good (E)-anti-diastereoselectivity (Table 2, entries 1, 3, 7). The regiochemistry of addition suggests that 15 is best represented as the isomer with the zirconium bonded ~g- to the silicon (c.f. 6), addition to the carbonyl group occurring via allylic rearrangement. 1 Addition of BF3 .Et20 decreased the anti:syn ratio, and small amounts of the (Z)-alkene isomer were formed (entry 2). Increasing the excess of the aldehyde improved the yield (entry 3 versus 1). Butanal and crotonaldehyde also reacted with 15 (Rl=Me) to give products 17 with excellent anti-stereocontrol (entries 4-6). The anti-stereochemistry of the major stereoisomers of 17 was proven by their conversion to the dienes 18 and 19 through either treatment with KH (known to be a syn-elimination) or with H2SO4 (known to be an anti-elimination) as shown in Scheme 2.14 The overall method comprises a useful three component synthesis of stereodefined conjugated dienes. Treatment of the vinylzirconocene 4c prepared by hydrozirconation of trimethylsilylacetylene with 14a afforded the disilylated allylzirconocene 20. Similarly to the reagents 15, the reaction of 20 with benzaldehyde was highly regio- and stereoselective and gave the allylsilane 21 as the anti-(E)-isomer.

cp Z c .,

R-

c, 14b n'

-90 to -60 °C, 1 h

L

]

ZrCp2CI

4a

15

16a (R 1 = Me), 6 9 %

i. R2CHO, ( B F 3 . E t 2 0 ) J

16b (R 1 = Pr), 38%

ii. NaHCO3aq ~ 1 "

R

6H13 + --

SiMe3 anti-17

R

6H13

Me3S~, -R1 syn-17

THF, 20"C, l h . or H2SO4 (cat), THF, 20°C, 3h

Scheme 2.

R

6H13 + R'

18

6H13 R1

19

9356 Table 2 Reaction of the allylzirconocenes 15 with aldehydes (Scheme 2) 17 Entry

R1

R2CHO a

1

6

Me Me Me Me Me Me

7

Pr

2 3 4 5

Elimination (KH)

Product

Yield% b

anti:syn c

PhCHO PhCHO/BF3.Et20 PhCHO e PrCHO PrCHO e MeCH=CHCHO e

a a a b

43 43 f 65 44

93 : 7

b

68

95 : 5

93

c

47

93 : 7

73 g

PhCHO e

d

29

>97 : <3

Elimination (H2SO4)

Yield(18+19)% d 1 8 : 1 9 c Yield (18 + 1 9 ) % d 1 8 : 1 9 c 92

8 : 92

88

92 : 8

7 : 93

70

91 : 9

89 : 11 94 : 6 95 : 5 10 : 90

a 1.3 equiv. R2CHO/(BF3.Et20), -78 *C to RT, then 18h RT. b Isolated yields based on 1-octyne. c Determined by 1H NMR analysis. 't Isolated yield based on 17. • 3 equiv. R2CHO used. f 4% of the product was (Z)-alkene, undefined syn : anti ratio, g Unstable.

Me3Si

.=

1. CP2ZrHCI / ~ rCp2CI 2. 14e Me3S~SiMe 3 20

1. P h C H O 2. H20

H ~ " ~ /~,.~ ~.SiMe3

PK ~ .

(2,)

v SiMe3

21, 46%

Overall, we have demonstrated an important convergent route to functionalised allylmetallic species with the formation of zirconated allylsilanes, and their reaction with aldehydes and ketones. Applications include efficient routes to 4,5-trans-disubstitituted y-lactones and stereodefined dienes.

Acknowledgements We thank the EPSRC for funding this work (GR/K19907).

References 1. Rousch, W. R. In Comprehensive Organic Synthesis; Trost, B. M.; Fleming, I., Eds.; Pergamon Press, Oxford, 1992; Vol. 2, pp. 1-54. Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93, 2207. Chan, T. H.; Wang, D. Chem. Rev. 1995, 95, 1279. 2. Kasatkin, A.; Nakagawa, T.; Okamoto, S.; Sato, F. J. Am. Chem. Soc. 1995, 117, 3881. Ito, H.; Nakamura, T.; Taguchi, T.; Hanzawa, Y. Tetrahedron 1995, 51, 4507. 3. Chino, M.; Matsumoto, T.; Suzuki, K. Synlett 1994, 359. Chino, M.; Liang, G. H.; Matsumoto, T.; Suzuki, K. Chem. Lett. 1996, 231. Maeta, H.; Hasegawa, T.; Suzuki, K. Synlett 1993, 341. 4. Brown, H. C.; Phadke, A. S.; Bhat, N. G. Tetrahedron Lett. 1993, 34, 7845. Matteson, D. S.; Majumdar, D. Organometallics 1983, 2, 1529. Tsai, D. J. S.; Matteson, D. S. Organometallics 1983, 2, 236. Matteson, D. S.; Majumdar, D. J. Organomet. Chem 1980, 184, C41. Hoffmann, R. W.; Dresely, S.; Lanz, J. W. Chem. Ber. 1988, 121, 1501. 5. Negishi, E.; Akiyoshi, K.; O'Connor, B.; Takagi, K.; Wu, G. J. Am. Chem. Soc. 1989, 111, 3089. 6. Negishi, E.; Akiyoshi, K. J. Am. Chem. Soc. 1988, 110, 646. 7. Sidduri, A.; Rozema, M. J.; Knochel, P. J. Org. Chem. 1993, 58, 2694. 8. Kocienski, P.; Barber, C. Pure andAppl. Chem. 1990, 62, 1933. 9. Fillery, S. M.; Gordon, G. J.; Luker, T.; Whitby, R. J. PureAppl. Chem. 1997, 69, 633. Gordon, G. J.; Whitby, R. J. Chem. Commun. 1997, 1321. Gordon, G. J.; Whitby, R. J. Chem. Commun. 1997, 1045. Tuckett, M. W.; Watkins, W. J.; Whitby, R. J. Tetrahedron Lett. 1998, 39, 123. Kasatkin, A.; Whitby, R. J. Tetrahedron Lett. 1997, 38, 4857. Kasatkin, A.; Whitby, R. J. J. Am. Chem. Soc. 1999, 121, 10208. 10. Wipf, P.; Jahn, H. Tetrahedron 1996, 52, 12853. 11. Burford, C.; Cooke, F.; Roy, G.; Magnus, P. Tetrahedron 1983, 39, 867. 12. Compound 6a: IH NMR (300 MHz, C6D6) 5:0.02 (9H, s), 1.0 (3H, t, J=6 Hz), 1.18 (IH, d, J=13.6 Hz, H-I), 1.2-1.4 (6H, m), 1.87 (2H, m, 2H-5), 2.18 (2H, m, 2H-4), 4.42 (IH, ddd, J=14.6, 8.0, 4.5 Hz, H-3), 5.20 (1H, dd, J=14.6, 13.6, H-2),

9357

5.56 (5H, s, Cp), 5.63 (5H, s, Cp) ppm; 13C NMR (75 MHz, C6D6) 8: -0.14, 12.74, 21,52, 28.01, 28.66, 30.62, 31.77, 59.56 (C-I), 108.18 (Cp), 109.40 (Cp), 121.20 (C-3), 125.91 (C-2) ppm.

~iMe3 ClCp2Z~Bu 2

4

13. The organic compounds 7a (not separated from 8a), 7b, 9a-g (with impurity of 10), 13, 17a--d (as anti:syn mixtures), 18a,b and 19a,b (each of the last two containing small amounts of the other) were fully characterised by t H and ~3C NMR, IR, MS, and either HRMS or microanalysis. 14. Peterson, D. J. J. Org. Chem. 1968, 33, 780. 15. The high anti-selectivity retained when the BF3.Et20 is added to the reaction mixture is surprising. Yamamoto reports a change from 96:4 to 19:81 anti:syn for the addition of crotylzirconocene chloride to benzaldehdye on addition of BF3-Et20. Yamamoto, Y.; Maruyama, K. J. Organomet. Chem. 1985, 284, C45. The difference in solvent (ether versus THF) may explain the discrepancy. See, also: Reetz, M. T.; Sauerwald, M. J. Org. Chem. 1984, 49, 2293. 16. Kosugi, H.; Tagami, K.; Takahashi, A.; Kanna, H.; Uda, H. J. Chem. Soc., Perkin Trans. 1 1989, 935. Fristad, W. E.; Peterson, J. R. J. Org. Chem. 1985, 50, 10. 17. Typical experimental: A solution of 4b was prepared by addition of l-benzyloxy-3-butyne (0.136 g, 0.85 mmol) to a suspension of Cp2Zr(H)CI (0.253 g, 0.98 mmol) in THF (3.5 mL) followed by stirring at 20°C for 1 h. To a solution of chloromethyltrimethylsilane (0.135 g, 1.10 mmol) in THF (9.0 mL) was added s-BuLi (0.94 mL, 1.24 M in cyclohexane, 1.16 mmol) at -78°C followed by TMEDA (0.135 g, 1.16 mmol). The reaction mixture was stirred at -78 to -60°C for 0.5 h then cooled to -78°C and the solution of 4b prepared above was added slowly. After warming to -40°C over 1 h a solution prepared from benzaldehyde (0.117 g, 1.10 mmol) and BF3.Et20 (0.156 g, 1.10 mmol) in THF (1.5 mL) was added and the mixture allowed to warm to room temperature. After stirring overnight sat. NaHCO3aq (6 mL) was added and the products were extracted into diethyl ether (3×6 mL). The organic layer was washed with brine (10 mL) and dried (MgSO4), the solvent removed and the crude product purified by column chromatography (25% ethyl acetate in 40-60 petroleum ether) to afford 9e (0.156 g, 52%). 18. Proven by comparison of carbon-13 NMRs with known compounds: Hoffmann, R. W.; Sander, T. Chem. Ber. 1990, 123, 145. 19. Chan, T. H.; Li, J. S. J. Chem. Soc., Chem. Commun. 1982, 969. 20. Cooke, F.; Magnus, P. J. Chem. Soc., Chem. Commun. 1977, 513.