Oxidation of acetals, an orthoester, and ethers by dioxiranes through α-CH insertion

Tcuahcdr.x~ Letters, Vol. 33, No. 29, pp. 42254228.1992 Printed in Great Britain

OXIDATION

CMO-4039/92 $5.00 + .oO Pcr&%non Press Ltd

OF ACETALS, DIOXIRANES

AN ORTHOESTER,

THROUGH

AND

ETHERS

BY

IX-CH INSERTlON

Ruggero Curci, *8 Lucia D’Accolti, Michele Fiorentino, Caterina Fusco Cenrro CNN. “M,I.S.U.“, Diportimen:u

di Chinka,

Unir~mitb r/i Rat-i, via Aswr~kda

17.3, l-70126

Bari. 110/y

and Waldemar Adam,* Maria E. GonzBlez-Nuiiez, Rossella Mello Imtirrt/j’iir

Key Work

Orgonrsche Chmic.

- Dioxiranes.

CH insertion,

U~rivernriil

Wiirzbwg. am Hublund, D-8700

Wiiribwg,

Oxygen transfer. AcetaJs. Ethers, Orthoesters,

F. R. G

Oxidation,

Cleavage.

Abstract. Dimethyldiorirane (la) and methyl(rrifluorometh~I)dlo\lrane (lb) effurntly itffurd cledvqc of acztala and of ke~als to c~rbanyl products under mild. neutml conditions Diakyl ethers arc cleaved IU alcohols. aldrhydcs and/
Using conventional the oxyfunctionalization

oxidation reagents, such as lead tetraacetate.1” dioxygen.lb

hydroperoxides.lc

or ozone,2

of ethers and acetals are rarely selective, as they often yield quite complex mixtures of

products; with cyclic ethers. products of oxidative cleavage often arise (Scheme l).* Scheme

1

Metal oxides in their high oxidation states.’ or LiOCl and catalytic amounts of Ru(I1) complexes4 count among the few reagents which are effective for the selective transformation of primary ethers into esters, without further oxidation of the esters to anhydrides and/or carboxylic acids. Also, metal nitrates - e.g., Cu(11) or Zn(I1) nitrate supported on silicagel have been employed to oxidize ethers under mild conditions to the corresponding

ketones

or aldehydes. with no further oxidation of the latter;” with this method. however. in some cases alkyl nitrites are formed as by-products5 Compared to oxidation methods which use metal oxides stoichiometrically oxidations employing

or metal complexes

catalytically,

either i/? sirlc h or isolated’ dioxiranes R’R*CO, (I), a new class of powerful oxidants,8

often have the advantages of simple procedures. mild reaction conditions, ease of product isolation, and increased yields. Thus, dimethyldioxirane

(la:

R1=R2=CH3)7a.9 and methyl(trifluoromethyl)dioxirane

(lb: R’=CH3,

R2=CF,)10 have been applied to perform an impressive variety of useful synthetic uar~sforlnations.6-13

4225

4226

Table

1. Oxidation of acetals and ethers by dioxiranes (la,b).

ItId

CH2CI?/acetone (30:70)

0

24 II

35

lbd

CH2ClflFP

(60:40)

0

2h

98

lbd

CH$&/TFP

(60:40)

0

30 111l.n

0

0

80

(95J ( >9.5)

0

(83) E

H&-W, (3)

18

lac

9611

50

(4) YCzH, C,H,O-7-H

lad

CH~CIZlacekm

(30:70)

0

2 11

95

la’

CH2Cl?/acelO1Ie (30:7O)

0

3 I1

50

M_tO-CH3 (7)

1 br

CClJ

0

IOmm

98

Q

la=

CHZCIZ/acetme (50~50)

0

7011

65

lbC

CH$lflFP

0

10 InhI

98

DC,& (5)

(60:4O)

Q.

(-Jo,

(9)

(8)

lb’

CH?C12iTFP i5O:SO)

0

15min

94

a, (12)

la< lb’

CH2Cltiacetone (40:60) CH2CIflFP (60:40)

18 10

9611 15mitl

(9:10=50 (9:10=65

(10)

~oH(12:13=8~ :a) (13)

30 85

In the course of a recent study on the oxidation of alcohols to carbonyl compounds observed that acetals and hemiacetals”

by dioxiranes,r’~r*

undergo easily oxidative cleavage to carbonyl-containing

these reagents. We present herein some further examples concerning the latter transformation, oxyfunctionalization

:20 )B JO )

of simple ethers. Representative results are shown in Table 1.

we

products by along with the

4227

Solutions of 0.06-0.09 M dimethyldioxirane (lb) in 1.l.l-trifluoropropanone

(la) in acetone or of 050.8

M methyl(trifluoromethyl)dioxirane

(its ketone precursor, hereafter TFP) were obtained by following the reported

protocol .7a*g~‘0The oxidations simply entailed addition of cold aliquots of standardized

9*10dioxirane solution

to the substrates (acetal, ether or otthoester) in dry CH,Cl, (kept at 0 “C, in the majority of cases). at the dioxirane excess and solvent composition

given in Table 1. The reaction progress was monitored by gc/ms; in some cases

(entries 2. 4,and 6, Table 1) ‘H NMR spectra were run periodically on the reaction mixture directly, in which case CD+& was employed in place of CH,Cl, as solvent. The first two entries in Table 1 estnbilish the dioxiranes as excellent agents for the oxidative cleavage of ethylene ketals 2 and 314 under mild conditions: as expected. tt the oxidation rates are much higher with dioxirane lb,loa which is several thousand-fold

more reactive15 than dimethyldioxirane

(la). This method should be synthetically

orthoesters) i/l the absence ofucid catalyst t

useful for the deprotection of masked carbonyl compounds (ace&,

Most likely. the oxidative cleavage is initiated by O-atom insertion into C-H bonds of the 1,3-dioxolane moiety of ketals 2 and 3. Similarly, dimethylacetal

initial O-insertions

(4) and of triethylorthoformate

substrates into methylbenzoate

by the dioxirane

into the methyne

C-H of benzaldehyde

(5) are also involved in the high yield transformation

and diethylcarbonate.

of these

respectively (entries 3 and 4, Table 1).

The products which arise from the cleavage of the simple. unbranched dialkyl ether such as 6 (Table 1) are also envisaged to derive from preliminary U-insertion selecti\x$~at methylene C-H Q to the ether moiety (Scheme 1). In accordance with these results. exposure of t-butyl methyl ether (7) to the action of the more powerful dioxirane lb brings about cleavage into formic acid and tert-butanol (which is resistant to further oxidation”). Interestingly,

ethers 8, 11, and 14

cleavage is not the main course of the dioxirane oxidation of medium-ring

(entries 7-9. Table 1). Rather. by using carefully dried dioxirane solutions (molecular sieves 5A), an alternative route - i.e.. oxidation to lactones (path ii , Scheme 1) - becomes the main process. lactones are accompanied

by variable amounts of the corresponding

(Table 1). Of interest is 3-methyltetrahydropyran place exclusively regioisomer

at the two a-CH2 positions

In most of the cases, the

acetals, the intermediate oxidation products

(14) as substrate (entry 9. Table I), for which insertion takes to afford a-methyl

&valerolactone

(1~5)‘~and its y-methyl

(16).*’ for the observed a functionalization

The high selectivity

speaks for a non-radical C-H insertion. akin to that

of alcohols. ’ ’ In fact, also some p attack would be expected in a

envisaged for the dioxirane oxyfunctionalization

classical radical pathway involving RO’ radicals: for instance. approximately 13% attack at P-CH, was found for the

reaction

of

tetrahydrofuran

3-methyltetrahydropyran

(8)

with

HO’.‘”

Concerning

this,

it should

be noted

that

for

(14) insertion at the p position should be encouraged by the presence of a tertiary C-H;

however, even in this case no product derived from @oxidation was detected. The results reported herein on the oxidations with dioxiranes provide a new entry into the cleavage of acetals to the corresponding

carbonyl products under mild conditions. as well as the direct conversion of cyclic ethers into

lactones, In view of the synthetic utility of these transformations.

further studies concerning

the elucidation of

mechanistic details of these C-H insertions are warranted.

Acknowledgement.

This work was supported

by the Italian National Research Council (C.N.R.) and by the “Progetto

Finalizzato _ C.F.“(C.N.R.). The work in Wiimburg was supported by the Deutsche Forschungsgemcinschaft Reuktiorw~

Meld-okfiricrl

Malrkiiie

at Universiry of Wiirzburg (F.R.G.).

(SFB 347, Se/eLlive

): R.M. and M. 8. G.-N. thank tie Alexander van Humboldt Foundation for fellowships spent

4228

References

and

Notes

1.

(a) Franze, V.: Edens, R. J~s/ns liebig Awt Chrm. 1970. 7.75. 47. (b) Heyns, K.: Buchholz. H. Chem. BL’T1976, 109, 3707. (c) Hosokawa, I.: Imuda. Y.: Murahashi. S.-I. J. Chetn Sot., Chem. Cojn~i. 1983. 1245.

2.

For a review, see: Keinan. E.: Varkony. H. T. in The Chemist OJ Fum-rwwl New York. 1983: Chapter 19, pp 649 ff : see also references therein.

3.

Schmidt, H.; Scheafer. H. Anger.

4.

(a) Bressan, M.: Morvillo. A. J. Chenr. kc.. Iriur-g. Chem. 1990.29, 2976.

5

Nishiguchi. T.: Bougauchi. M. J. Org. Chevi. 1990,55,

6.

(a) Edw~ards. J. 0.; Pater. R. H.; Curci, R.: Di Furia. F. Phntorhenr. Photobial. 1979. .lO, 63. (b) Curci. R.; Fiorentino, M.; Troisi. L.; Edwards. J. 0.: Parer. R. H. J Org. Chm. 1980.45, 475. (c) Cicala, G.: Cut-ci. R.; Fiorentino, M.: Laricchiuta, 0. J Org. Chew. 1982.47, 2679. (d) Curci. R.; Fioremino. M.; Serio. M. R. .I. Chctv. Sot.. Clovn. Co,nm. 1984, 1.55.

7.

(a) Murray,

R. W.; Jeyaraman.

Chm

Ir,t.Ed.

Engl. 1979, 18, 69

; and

Gwr/pps. Pem~ides

references

Chrr~r. Conmt. 1989. 421.

, Patai, S.,Ed.; Wiley:

quoted

(b) Bressan. M.; Morvillo, A.; Romanello, G.

5606.

R. J. Org. Chon. 1985, 50. 2847.

(b) Munay.

R. W.: Singh. M: Jeyaraman.

R.

J. Am. Chew. Sm. 1992. 114, 1346.

a.

For reviews. see: (a) Adam, W.; Curci. R.: Edwards, J. 0. Ace. Chem. Res lY8Y, 22, 205. (b) Murray, R. W. Chem Rev. 1989,89, 1187. (c) Curci. R. in Adwrrces irr O.tygtwared Processes: Baumstark, A. L., Ed.: JAI: Greenwich, CT, 1990: Vol 2, Chapter I. (d) Adam. W.: Hadjiarapoglou. L. P.; Curci, R.; Mello, K. in Urgariir Perodes; Ando, W., Ed.; Wiley, New York: Chapter4. in press. (e) Adam. W.: Hadjiarapoglou. L. P. Topics Cur-r. Chew. in press.

9.

(a) Cassidei. L.: Fiorentino, M.: Mello. R.: Sciacovelli. 0.: Curci, R. J Org. Chern. 1987, (b) Adam. W.: Chair, Y.-Y: Cremer. D.; Gauss, J.: Scheutzow, D.; Schindler. M. J Org. Chem. 1987.52, 2800.

10.

(a) Mello. R.: Fiorentino. M.: Sciacovelli. 0.: Curci. R. J. 0,g C‘hcn 1988. 53. 3890. (b) Mello. R.; Fiorentino, M.: Fusco. C.; Curci. R. J. Am Chen? Sm. 1989. J II, 6749. (c) Adam. W.: Curci, R.: Gonzalez-Nufiez. M. E.: Mello, R. J. Ant Chem. Sm. 1991. 113. 7654.

11.

Mello, R.: Cassidei, L.; Fiorentino. M.; Fusco. C.: Htimmer. W.: JBger. V.; Curci, R. J. Am. Chem. Sm. 1991, 113. 2205.

12.

Abou-El&tab,

13.

For some recent examples, see: (a) Adam, W.: Asensio. G.: Curci, R.; Gonzales-Nuiiez, M. E.; Mello, R. J. 01%. Chem. 1992,57, 953. (b) Brown, D. S.: Marples. B. A.: Muxworthy. J. P.: Baggaley, K. H. d. Chcm. Resrmch /S) 1992, 28. (c) Bovicelli. E Lupattelli. P.: Mincione, E.: Prencipe. T.; Curci. R. J. 0~ Chest. 1992,57. in press.

14.

Dauben. H. J.: Loren. B.; Ringold, H. J. J. A m Chent. Sot. 1954. 76. 1359.

1.5.

Mello, R.: Cassidei. L.; Fiorentino. M.: Fusco. C.: Curci, R. Tetrahckorf

16.

(a) 3-Methyl-tetrahydropyran-(2H).2-one (15): bp 71-75 “C (6 mmHg) 16b; ft-ir: 1776 (C=O str.). 1141 (C-O str.) cm-l, etc.; 1H nmr (CDC13, 200 MHz) 8 1.22 (d, 3 H. CH3. J = 6.9 Ha), 1.3 - 2.2 (camp’?x m, 3 I-I). 2.55 (m, 2 H. CH2), 4.25 (m. 2 H); ms (70 eV) TX/Z (I’. i.) 114 (28. M+), 99 (4), 70 (15, ‘CH2CH(CH3)CrOf 1. 55 (100, [jnlz 70-CH3] ), 42 (98). etc.. (b) Kurata, K.; Tanaka. S.; Takthashi. K. Chem Phorm. Bull. (Tdioi 1976.24, 538.

17.

(a) S-Methyl-tetrahydropyran-(ZH).Z-one (16): bp 86 ‘C (2 nnnI-Ig) t’b; ft-ir: 1781 (C=O str.), 1144 (C-O str.) cm-t, etc.: 1H nmr (CDC13. 200 MHz) 6 0.98 (d. 3 H. CHJ. J = 6.6 Hz). 1.2 - 2.2 (m. 3 H). 2.40 (m. 2 H. CH2). 3.90 (m ,2 H,

M.; Adam, W.: Saha-Miiller. C. R. Liebig.r Auu Chm

(a) C. Walling. G. M. El-Taliawi and R. A. Johnson. /. Am. Chm 1975,8. 125.

(Received in UK 13 April 1992)

699.

1991. 44.5.

L&I. 1990.31.

3067

CH2); ms (70 eV) m/z (r. i.) 114 (14. M+). 84 (16). 70 (17). 56 (81. ‘CH2CH2C=O+ (b) Surzur, J.-M.: Teissier, P. 8~11. Snc. Chum. Fru~~ce 1970. 653.

18.

52,

1. 55 (51). 42 (loo),

etc..

Ser. 1974, 96. 133. (b) C. Walling. Arc. Chcm. Res.