Stereochemical studies of monoterpene compounds. Part XI. Rearrangement of 2α-hydroxypinan-3-one in the presence of anhydrous oxalic acid

Abstract

Treatment of (+)-2α-hydroxypinan-3-one (1) with anhydrous oxalic acid led to the formation of eucarvone (2), carvacrol (3), (+)-dihydro-β-campholenolactone (1,8,8-trimethyl-2-oxabicyclo[3,3,0]octan-3-one)(4), (–)-1,2-campholide (1,8,8-trimethyl-2-oxabicyclo[3,2,1]octan-3-one)(5), (±)-carvone (6), and (+)-α-campholenic acid (7). Conversion of (+)-2α-hydroxypinan-3-one (1) into the ketone (2) and the lactones (4) and (5) is a novel acid-catalysed rearrangement of the pinane skeleton. The mechanistic implications of the rearrangement are discussed.