Synthesis of an alberta oil sand bitumen C20 tricyclic carboxylic acid bearing a novel diterpenoid skeleton

Abstract

The synthesis of (±)-13-norisocopalane-15-carboxylic acid (9), for comparison with the C₂₀ carboxylic acid found in Alberta oil sand bitumen, is described. It involves the preparation of the key intermediate (±)-methyl 16-norisocopalan-l5-oate (27), by transformation of the known allylic alcohol (20), and homologation of (27)via the nitrite (30). Comparison of natural and synthetic methyl ester derivatives unequivocally established the correctness of the structure (9) for the natural product.