Preparation of optically active cyclohexenones: Chirons for the lipophilic moiety of flowery‐ and woody‐like odorant ketones

Optically active 2,5,6,6‐ and 2,4,4,5‐tetraalkylcyclohex‐2‐en‐1‐ones ((+)‐2a–d and (−)‐5a–d), important building blocks for flowery‐ and woody‐like odorants, have been prepared. Compounds (+)‐2a–d and (−)‐5a–d were obtained by ozonolysis of the corresponding cyclopentenic precursors, followed by intramolecular aldol condensation. Alternatively, enones (+)‐2a–d were reduced to the corresponding allylic alcohols ad converted to enones (‐)‐5a–d via acidic isomerization and oxidation. 13C‐NMR assignments are presented.