Novel steroidal chiral auxiliaries: Enantioselective synthesis of chiral α-hydroxy acids

✍ Scribed by Deeng-Lih Huang; Richard W. Draper

• Publisher: Elsevier Science
• Year: 1994
• Tongue: French
• Weight: 161 KB
• Volume: 35
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)75783-2

✦ Synopsis

The synthesis is reported of three novel steroidal chiral auxiliaries (4) which were used to generate an a-hydroxy acid in high optical parity (90-9896 cc).

Chiral auxiliaries for enantioselective syntheses are of current interest13 Cyclohexyl based chiial auxiliaries, such as menthol, S-phenylmenthol, and rrrmr-2-phenylcyclohexanol, have been used for various asymmetric inductions.'-2 Herein we report the synthesis and application of three novel steroidal chiral auxiliaries (4) for enantioselective synthesis. The steroidal chiral auxiliaries are readily derived from natural sources, am highly crystalline and easily recovered. Furthermore, their preparation requires no enzymatic resolutionl~

The steroidal chiral auxiliaries (4) were synthesized in three steps (Scheme 1).3 So-CholestanS-one (1)

was arylated and transformed, either by Grignard or by lithium reactions, into the tertiary alcohols (2) which were then dehydrated to the olefins (3) with thionyl chloride or phosphorous oxychloride in pyridine at room