SYNTHESIS OF PENTALENIC ACID THROUGH BIOGENETIC LIKE CYCLIZATION OF HUMULENE

Abstract
Humulene furnished 4,7-epoxy-3-methylene-7,10,10-trimethyl-11-bicyclo[6,3,0]undecanol 9 in 34% yield employing oxymercuration as a key step. On treatment with BF3·OEt2,7,11-dihydroxy-3,7,10,10-tetramethyl-3-bicyclo[6.3.0]undecene, which was derived from 9 by ether cleavage, afforded 10α-hydroxypentalenene 13 (20%) along with four byproducts. Oxidation of allylic methyl group of 13 gave methyl pentalenate in 13% yield from 9.