Cyclohexenones Michael/Wittig reaction

A stereoselective [3 + 3] annulalion by a Michael-Wittig reaction on the enal 82 derived from 2,3-0-isopropylidene-(/ )-glyceraldehyde and ethyl-3-oxo-(triphenyl phosphoryU-dene) butanoate (69)" in one pot gave the cyclohexenone derivative 83. Enone reduction and stereoselective dihydroxylation led to formation of highly functionalized cyclohexane systans (85a to 85c) (Schone 22.19). 

Scheme 7.35 Cascade Michael/Wittig reaction for the synthesis of cyclohexenones.

The reaction of (3-carbethoxy-2-oxopropylidene)triphenylphosphorane (37) with ,13-unsaturated aldehydes in the presence of base provides a new synthesis of cyclohexenones in moderate yield, presumably via an intramolecular Wittig reaction of the initial Michael addition product (38) (Scheme 6). Olefina-tion of aldehydes with methyl 5-(triphenylphosphoranylidene) levalinate (39) proceeds in excellent yield and so provides a method of homologation to S-ene-Y-keto esters in one step. 

Similar [3-1-3] reactions of a,p-unsaturated aldehydes initiated by iminium-medi-ated Michael addition, followed by aldol [120], Knoevenagel [121], or Wittig [122] reactions to generate 2-cyclohexenones, were also developed. 

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