Synthesis of long chaina,B‐alkynoic anda,B‐alkynoic acids viaB‐keto esters

Abstract

AbstractA general method for the synthesis of long chain α,β‐alkynoic acids from β‐keto esters is described. The synthesis involves conversion of the β‐keto ester to the corresponding pyrazolone, then halogenation and treatment of the resultant 4,4‐dihalo product with dilute aqueous alkali to form the α,β‐alkynoic acids. Specifically, 2‐octynoic, 2‐nonynoic and 2‐decadecynoic acids were prepared as representative examples. If the β‐keto ester has an alkyl group at the α‐position, the final product is a mixture ofcis andtrans α‐substituted‐α,β‐unsaturated alkenoic acids, which may be separated by gas‐liquid chromatography. Pertinent IR and proton magnetic resonance data are used in characterizing the stereochemistry of products and a possible mechanism for the product forming reactions is presented.