Hydroxy-directed diastereoselective ene reaction of triazolinediones with chiral allylic alcohols

The ene reaction of the N-methyltriazolidinone (MTAD) with the allylic alcohols la-e afforded the corresponding urazoles 2 in high three diastereoselectivity (Scheme 1). These results are mechanistically explained in terms of an attractive hydrogen-bonding interaction between the enophile and the allylic hydroxy functionality in the three transition state, which is favored on account of minimal 1,3-allylic strain. The three diastereoselectivity is completely lost when the allylic hydroxy-functionality is masked. The results parallel the hydroxy-directing effect previously established in the singlet-oxygen ene reaction. (C) 1998 Elsevier Science Ltd. All rights reserved.