Dimethylaluminum methide complex Tf2CHAIMe2:: an effective catalyst for Diels-Alder reaction of α,β-unsaturated lactone derivatives with cyclopentadiene

Lewis acid derived by mixing Tf2CH2 and Me(3)AI was found to be an effective catalyst system for the catalytic DA reaction of less reactive a, P-unsaturated lactone derivative with cyclopentadiene (CP). In this catalyst system, Tf(2)CHAIMe(2) is an active species and an excess amount of Me3AI plays an important role to lower the catalyst loading. Substituent effect of the lactone framework on pi-facial selectivity was also examined. In the reactions of both gamma-substituted 5-membered lactone derivatives and gamma- or delta-methylated 6-membered lactone derivatives with CP, selective attack on the anti face of gamma- or delta-substituent was observed. On the other hand, in the cases of gamma- or epsilon-methylated 7-membered lactone derivatives, CP favorably attacked on the syn face. (c) 2007 Elsevier Ltd. All rights reserved.