Convergent, enantioselective syntheses of guanacastepenes A and E featuring a selective cyclobutane fragmentation.
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 pi-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.
Shipe
William D
WD
Frick Chemical Laboratory, Princeton University, Princeton, NJ 08544-1009, USA.
Sorensen
Erik J
EJ
D002625:Chemistry, Organic / Q000379:methods*; D003432:Cross-Linking Reagents / Q000737:chemistry; D003503:Cyclobutanes / Q000737:chemistry*; D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D003432:Cross-Linking Reagents; D003503:Cyclobutanes; D004224:Diterpenes; C454620:guanacastepene A; C516935:guanacastepene E