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Monday, January 9, 2012
Douglass F. Taber
University of Delaware

Stereoselective C-O Ring Construction: The Keck Synthesis of Bryostatin 1

Vladimir Gevorgyan of the University of Illinois, Chicago homologated (Angew. Chem. Int. Ed. 2011, 50, 2808. ) the ketone 1 to the epoxide 2 using cyanogen bromide. Manabu Abe of Hiroshima University optimized (J. Am. Chem. Soc. 2011, 133, 2592. ) the diastereoselectivity of the Paternò-Büchi addition of benzophenone (4) to the secondary allylic alcohol 3, to give 5.

Debaraj Mukherjee of the Indian Institute of Integrative Medicine constructed (Org. Lett. 2011, 13, 576. ) the lactone 7 by adding acetate to 6, with remarkable regio- and diastereoselectivity. Tristan H. Lambert of Columbia University employed (Org. Lett. 2011, 13, 740. ) cyclopropenium activation to cyclize the diol 8 to 9.

Brian L. Pagenkopf of the University of Western Ontario designed (Org. Lett. 2011, 13, 572. ) a Co catalyst for the diastereoselective oxidative cyclization of 11 to 12. Goverdhan Mehta of the Indian Institute of Science, Bangalore, found (Tetrahedron Lett. 2011, 52, 1749. ) that the Z-diene 13 cyclized efficiently, to give the cyclic ether 14.

Fabien Gagosz of the Ecole Polytechnique found (J. Am. Chem. Soc. 2011, 133, 7696. ) that the protonated complex derived from the allene 15 abstracted a hydride from the distal benzyl group, leading to cyclization to 16. Haruhiko Fuwa of Tohoku University found (Org. Lett. 2011, 13, 1820. ) that the unsaturated thioester 17 cyclized under gentle acid catalysis. Unsaturated esters (not illustrated) can be cyclized under alkaline conditions (Tetrahedron Lett. 2011, 52, 1372. ).

Malcolm D. McLeod of the Australian National University established (J. Org. Chem. 2011, 76, 1992. ) a combination of E. coli-derived enzyme and an α-D-glucuronyl fluoride donor for converting an alcohol 19 to the corresponding glucuronide metabolite 20. En route to an improved synthesis of the schweinfurthins, potent anti-neoplastic agents, David F. Wiemer of the University of Iowa devised (J. Org. Chem. 2011, 76, 909. ) the cyclization/benzyloxmethyl transfer cascade that transformed 21 into 22.

The synthesis and biological activity of the brytostatins is developing into one of the great success stories of natural products chemistry. A key step in the total synthesis of Bryostatin 1 (25) designed (J. Am. Chem. Soc. 2011, 133, 744. ) by Gary E. Keck of the University of Utah was the Rainier cyclization of 23 to 24.

D. F. Taber, Org. Chem. Highlights 2012, January 9.