Chiral olefinic acetals derived from crotonaldehyde undergo ionic Diels- Alder reaction giving the corresponding cycloadducts in moderate to good diastereoselectivities. A variety of achiral olefinic acetals react with isoprene and cyclopentadiene to form the cycloadducts in good to excellent yields when catalysed by 4M LiClO4 in nitromethane or by Nafion-H in dichloromethane.
Bibliographical noteFunding Information:
We thank the Department of Science and Technology, New Delhi, for financial support through a project (No. SP/S1/G-22/91). One of us (R. Kumareswaran) thanks the Council of Scientific and Industrial Research, New Delhi, for the award of a Senior Research Fellowship. We thank Profs. G.A. Olah and G.K.S. Prakash for the gift of Nation K.