Borane-mediated aldol cycloreduction of monoenone monoketones: diastereoselective formation of quaternary centers.J Org Chem. 2003 Jan 10; 68(1):11-4.JO
Exposure of monoenone monoketones to catecholborane in THF at ambient temperature results in tandem 1,4-reduction-aldol cyclization. For aromatic and heteroaromatic enones, six-membered cyclic aldol products are formed in excellent yield with high levels of syn diastereoselectivity. Five-membered ring formation proceeds less readily, but the yield of cyclized product is improved through introduction of Rh(I) salts.