Base‐Induced Decarboxylation of Polyunsaturated α‐Cyano Acids Derived from Malonic Acid: Synthesis of Sesquiterpene Nitriles and Aldehydes with β‐, φ‐, and ψ‐End Groups

Catalytic base-induced decarboxylation of polyunsaturated alpha-cyano-beta-methyl acids derived from malonic acid led to the corresponding nitriles 3 (Schemes 2 and 3), 6 (Scheme 5), and 9 (Scheme 6). This decarboxylation occurred with previous deconjugation of the alpha,beta-alkene moiety of the alpha-cyano-beta-methyl acid, leading to an alpha-cyano-beta-methylene propanoic acid which was easily decarboxylated (see Scheme 2). beta-Methylene intermediates, in some cases, could be isolated; mechanistic pathways are proposed. The nitriles 3, 6, and 9 were reduced to the sesquiterpene aldehydes 4 (beta-end group), 7 (phi-end group), and 10 (psi-end group), respectively.