The Remarkable Effect of Cosolvent on a Samarium(II)-Mediated 4-<i>exo-trig</i> Cyclization:  Further Synthetic Studies on Pestalotiopsin A

Abstract

A samarium(II)-mediated 4-exo-trig cyclization in which a remote stereocenter serves to control the facial selectivity of the cyclization is described. The apparent coordination of a tert-butyldimethylsilyl ether to the samarium center appears to give rise to the selectivity. The remarkable effect of the cosolvent, 2,2,2-trifluoroethanol, on the cyclization of this substrate, is also discussed. A stereoselective synthesis of the general class of gamma,delta-unsaturated aldehyde cyclization substrate is reported, and the utility of the cyclization is demonstrated in an approach to the fully functionalized core of pestalotiopsin A.