Virtually complete asymmetric induction is achieved during methyl-, vinyl-, and naphthylmetallic conjugate addition to enantiomerically pure (S)-(+)-2-(p-tolylsulfinyl)-2-cyclopentenone ((S)-(+)-1). (R)-3-Methylcyclopentanone is obtained when the enone sulfoxide (S)-(+)-1 is first complexed with divalent zinc and then methylmagnesium iodide is added, whereas (S)-3-methylcyclopentanone is obtained when methylmagnesium iodide is added to the same, uncomplexed enone sulfoxide. (R)-3-Methylcyclopentanone is obtained also when the enone sulfoxide is treated separately with lithium tetramethylaluminate, methyltitanium triisopropoxide, and methylmagnesium chloride. (S)-(+)-2-(1-Naphthylsulfinyl)-2-cyclopentenone ((S)-(+)-1′) gives mainly the unexpected (S)-3-methylcyclopentanone on reaction with dimethylcopperlithium. Enantiomerically pure steroid intermediates (S,S)-(+)-4 and (S,S)-(+)-7 are prepared in short, convergent, and high-yield sequences starting with enone sulfoxide (S)-(+)-1.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry