Aldehydes adjacent silyl group

Alkenes can also be obtained by reaction of the silylated p-tosylhydrazone of saturated aldehydes with a vinyllithium. Of further interest, no epimerization occurs at centers adjacent to the aldehyde group. The (E)-configuration is favored in the case of both di- and trisubstituted alkenes. 

Bioactive compounds that contain the difluoromethylene group adjacent to the carbonyl functionality have been the subject of increased research efforts in recent yearsf 59). The most widely utilized methods that have been employed to introduce this group into organic molecules have been (a) Reformatsky reaction of halodifluoroacetates (60-66) (b) elaboration of difluoroketene silyl acetals (67-69) (c) metal catalyzed addition of 3-bromo-3,3-difluoropropene to aldehydes and ketones (70) and (d) alkylation of CuCF2COOR(77). The modest yields associated with these methods prompted us to explore alternative methodology for the preparation of this useful building block. 

Steric effects of the hexacarbonyldicobalt moiety may be responsible for altered reactivity, notably enhanced stereoselectivity in reactions of adjacent substituents, e.g. formyl groups in aldol condensations. Thus, condensation of trimethylsilylpropy-nal with the silyl enol ether of cyclopentanone gives a 90% yield of the aldol product (eq 50) as a 40 60 erythro threo mixture, whereas reaction of the Co2(CO)6-complexed aldehyde followed by cerium(IV) oxidation gives the same total yield, but in an 87 13 diastereomeric ratio. ... 

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