Synthesis of 2-(S)-[(4-methylphenyl)sulfinyl]-2-cyclopenten-1-one, a D-ring precursor of 9,11-secosterols

The asymmetric oxidation of a key intermediate for 9,11-secosterol synthesis, 2-[(4-methylphenyl)thio]-2-cyclopenten-1-one 2 with a Ti(iPrO)4/(+)-DET/TBHP complex was studied. The kinetic resolution of racemic 2-[(4-methylphenyl)sulfinyl]-2-cyclopenten-1-one 1 by oxidation with the same Ti-complex was also carried out. In both cases enantioenriched 2-(S)-[(4-methylphenyl)sulfinyl]-2-cyclopenten-1-one 1 was obtained in satisfactory yields and sufficient enantiomeric purity for further enantioenrichment by recrystallization. The obtained results afford simple access to the D-ring precursor of 9,11-secosterols.