Synthesis of Naturally Occurring Polyynes

Graphical Abstract

Diverse structures and biological activities are shown by polyyne natural products (such as the compounds shown, isolated fron Anacyclus pyrethrum). Although some polyynes can be assembled with relative ease, most present a considerable synthetic challenge because of either a highly conjugated and unstable framework or stereochemical considerations. Recent strategies for the synthesis of these fascinating molecules are discussed.

Abstract

Over the past fifty years, hundreds of polyyne compounds have been isolated from nature. These often unstable molecules are found in sources as common as garden vegetables and as obscure as bacterial cultures. Naturally occurring polyynes feature a wide range of structural diversity and display an equally broad array of biological properties. Early synthetic efforts relied primarily on Cu-catalyzed, oxidative acetylenic homo- and heterocoupling reactions to assemble the polyyne framework. The past 25 years, however, have witnessed a renaissance in the field of polyyne natural product synthesis: transition-metal-catalyzed alkynylation reactions and asymmetric transformations have combined to substantially expand access to natural polyynes. This Review recounts these synthetic achievements and also highlights both the natural source(s) and biological relevance for many of these compounds.