Borane-Mediated Aldol Cycloreduction of Monoenone Monoketones: Diastereoselective Formation of Quaternary Centers
Ryan R. Huddleston, David F. Cauble and Michael J. Krische*
*Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, Email: mkrischemail.utexas.edu
R. R. Huddleston, D. F. Cauble, M. J. Krische, J. Org. Chem., 2003, 68, 11-14.
A tandem 1,4-reduction-aldol cyclization is induced by exposure of monoenone monoketones to catecholborane in THF at ambient temperature. Six-membered cyclic aldol products are formed in excellent yield with high levels of syn diastereoselectivity for aromatic and heteroaromatic enones. Five-membered ring formation proceeds less readily, but the yield is improved through addition of Rh(I) salts.
see article for more examples
stereochemical model accounting for the syn diastereoselectivity
T.-G. Baik, A. L. Luis, L.-C. Wang, M. J. Krische, J. Am. Chem. Soc., 2001, 123, 5112-5113.