Acetals with cyclohexene silyl

Moreover, the formation of enoxy-silanes via silylation of ketones127 by means of N-methyl-N-TMS-acetamide (1 72) in presence of sodium trimethylsilanolate (173) was reported in 1969 and since then, the use of silylating reagents in presence of a catalyst has found wide appreciation and growing utilization as shown in recent papers128-132 (Scheme 27). Diacetyl (181) can be converted by trifluoromethylsul-fonic acid-TMS-ester (182) into 2,3-bis(trimethylsiloxy)-l, 3-butadiene (7treatment with ethyl TMS acetate (7 5)/tetrakis(n-butyl)amine fluoride l-trimethylsiloxy-2-methyl-styrene (i<56)130. Cyclohexanone reacts with the combination dimethyl-TMS-amine (18 7)/p-toluenesulfonic acid to 1-trimethylsiloxy-l-cyclohexene (iSS)131. Similarly, acetylacetone plus phenyl-triethylsilyl-sulfide (189) afford 2-triethylsiloxy-2-pentene-4-one (790)132. ... 

Enol silyl ethers react with aldehydes with a catalytic amount of TBAF to give the aldol silyl ethers in good yields. These reactions generally proceed under very mild conditions and within shorter periods of time than conventional strong acidic or basic conditions. The products from4-f-butyl-l-methyl-2-(trimethylsilyloxy) cyclohexene and benzaldehyde show very good axial selectivity and a little anti-syn selectivity (eq 20). The aldol condensation of ketones and aldehydes can be achieved in one pot when ethyl (trimethylsilyl)acetate is used as a silylation agent with TBAF (eq 21). 

Allylsilane Model 5. The synthesis of the acetal models derived directly from our previously described aldehyde model 1, and took advantage of common intermediates. Alcohol 9, available in 5 steps from 2-cyclohexen-l-ene, was converted to key intermediate 12a by routine functional group manipulations, Scheme 4. Reductive silylation of 12a and chromatographic removal of the allylic isomer produced the target 5a, Scheme 5. The other substrates were prepared from 12a by acetal exchange with the desired alcohol followed by reductive silylation as above to provide the ethyl (5b), isobutyl (5c) and isopropyl (5d) acetal models. Scheme 5. 

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