Syntheses of cis- and trans-7-Chloro- 7,8,9,10-tetrahydrobenzo[a]pyren-8-ol: A Remarkable Solvent Effect on Epoxide Hydrochlorination Diastereoselectivity

Abstract

Cis- or trans-7-chloro-7,8,9,10-tetrahydrobenzo[a]pyrene-8-ol were prepared from the corresponding epoxide in good selectivity and yield via LiCl hydrochlorination in different solvents. These preparations take advantage of a dramatic solvent effect on the hydrochlorination diastereoselectivity. Cis products strongly predominate in chlorinated hydrocarbons, and alternatively, trans chlorohydrin formation occurs in high selectivity in Et₂O, THF, and acetone. This solvent effect was not significant for other halide salts.

Keywords:

• Epoxides
• Carbocations
• Ring opening
• Solvent effects
• Stereoselectivity reversal

Acknowledgment

This work was supported by grants from The Welch Foundation (#96-086) and NIGMS (S06 GM08194). We thank Justin King, Roberto Alcorta, and Dr. Larry Ytuarte for technical support.