Exploration of Dicaranyl Methyl Borate for Asymmetric Epoxidation- Synthesis of Pheromone Intermediates

Abstract

A novel method to generate chiral cis-epoxide, an intermediate for the synthesis of disparlure pheromone was explored. Under in situ condition, reaction between allyl chloride and (-)b-methoxydicaranylborane in the presence of LiN(cy-hex)₂ (DCHA) and diethyl ether yielded an ate complex, [(a-chloroallyl)lithium]. This ate complex on further reaction with (BF₃.OEt) at -95 ºC resulted in the formation of a reagent [(Z)-g-chloroallylBcar²]. The reagent thus formed on further chloroallylboration using an aldehyde, followed by elimination of chiral auxiliary provided syn-a-chlorohydrins in high ee (> 95 %). Base induced cyclization of chlorohydrins furnished chiral cis-vinylepoxides. (-)b-methoxydicaranylborane showed better results than (-)b-methoxydiisopinocamphenyl borane and was also economical. This methodology was further experimented for pheromone synthesis. By this process we have successfully synthesized the key intermediate of Disparlure cost effectively.