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 α ‐cyano‐ β ‐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 α , β ‐alkene moiety of the α ‐cyano‐ β ‐methyl acid, leading to an α ‐cyano‐ β ‐methylene propanoic acid which was easily decarboxylated (see Scheme 2 ). β ‐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 ( β ‐end group), 7 ( φ ‐end group), and 10 ( ψ ‐end group), respectively.