Direct Aldehyde Homologation Utilized To Construct a Conjugated-Tetraene Hydrocarbon Insect Pheromone

Richard J. Petroski* and Robert J. Bartelt
Crop Bioprotection Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604
J. Agric. Food Chem., 2007, 55 (6), pp 2282–2287
DOI: 10.1021/jf063337e
Publication Date (Web): February 24, 2007
Copyright Not subject to U.S. Copyright. Published 2007 American Chemical Society
*

 Corresponding author:  e-mail petrosrj@ncaur,usda.gov.

Abstract

New phosphonate reagents were developed for the two-carbon homologation of aldehydes to methyl- or ethyl-branched unsaturated aldehydes and used in the practical synthesis of (2E,4E,6E,8E)-3,5-dimethyl-7-ethyl-2,4,6,8-undecatetraene (1), a pheromone of the beetle Carpophilus lugubris. The phosphonate reagents, diethyl ethylformyl-2-phosphonate dimethylhydrazone and diethyl 1-propylformyl-2-phosphonate dimethylhydrazone, contained a protected aldehyde group instead of the usual ester group. A homologation cycle entailed condensation of the reagent with the starting aldehyde, followed by removal of the dimethylhydrazone protective group with a biphasic mixture of dilute HCl and petroleum ether. This robust two-step process replaces the standard three-step aldehyde homologation route using ester-based Horner−Wadsworth−Emmons reagents. The new synthesis of compound 1 from (2E)-2-methyl-2-butenal was run on a 10-g scale and required just five steps (two cycles of condensation and deprotection, followed by a final Wittig olefination) instead of the usual seven. In addition, the Wittig olefination step was simplified and its E-isomer selectivity was improved. The overall yield for the entire synthetic pathway was increased from 20% to 37%, enhancing the commercial potential of Carpophilus pheromones.

Keywords: Aldehyde homologation; diethyl ethylformyl-2-phosphonate dimethylhydrazone; diethyl 1-propylformyl-2-phosphonate dimethylhydrazone; sap beetle; Carpophilus lugubris; Nitidulidae

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History

  • Published In Issue March 21, 2007
  • Received for review November 17, 2006. Revised manuscript received January 24, 2007. Accepted January 25, 2007. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

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