Reactions of diterpenoids in concentrated sulphuric acid. Part 1. Novel rearrangements of tetrahydroabietic acids

Abstract

Dissolution of 8β,13βH-, 8β,13αH-, and 8α,l3αH-tetrahydroabietic acids (1), (2), and (4), respectively, in cold concentrated sulphuric acid led to decarbonylation, followed by a novel skeletal rearrangement, and recarbonylation to give inter alia(±)-2βH,4aα,4bβ,8aα,10aβ-tetradecahydro-α,α,8,8-tetra methylphenanthren-2-ylacetic acid (5) and (±)-4aα,4bβ,8aα,10aβ-tetradecahydro-8,8-dimethyl-2ξ-(1-methylethyl)phenanthrene-2-carboxylic acid (12). The structures of these rearrangement products have been determined and preliminary experiments have indicated a possible mechanism for their formation.