Convergent, Enantioselective Syntheses of Guanacastepenes A and E Featuring a Selective Cyclobutane Fragmentation1

William D. Shipe† and Erik J. Sorensen*
Contribution from the Frick Chemical Laboratory, Princeton University, Princeton, New Jersey 08544-1009
J. Am. Chem. Soc., 2006, 128 (21), pp 7025–7035
DOI: 10.1021/ja060847g
Publication Date (Web): May 10, 2006
Copyright © 2006 American Chemical Society
†

 Current address:  Merck Research Laboratories, West Point, Penn-sylvania.

,
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, ejs@princeton.edu

Abstract

Abstract Image

The evolution of a convergent strategy that led to efficient, enantioselective syntheses of both natural (+)- and unnatural (−)-guanacastepene E and formal total syntheses of (+)- and (−)-guanacastepene A is described. A union of five- and six-membered ring intermediates by an efficient π-allyl Stille cross-coupling reaction was followed by an intramolecular enone-olefin [2 + 2] photocycloaddition and a stereoelectronically controlled, reductive fragmentation of the resulting cyclobutyl ketone. The latter two transformations enabled controlled formation of the C-11 quaternary stereocenter and the central seven-membered ring of the guanacastepenes. An enantiospecific synthesis of the functionalized five-membered ring vinyl stannane from the monoterpene R-(−)-carvone featuring a carbon−carbon bond forming ring contraction was also developed.

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History

  • Published In Issue May 31, 2006
  • Received February 4, 2006

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