2002 Cycloaddition reactions

Cycloaddition reactionsO 0070 Trimethylsilyl Bis(trifluoromethanesulfonyl)imide as a Tolerant and Environ-

mentally Benign Lewis Acid Catalyst of the Diels—Alder Reaction. — The Lewis acid Tms-NTf2, smoothly prepared by protodesilylation of trimethylsilane, allyl- or phenyltrimethylsilane with bis(trifluoromethylsulfonyl)imide, represents a very effec-tive catalyst for Diels—Alder reactions. It is more reactive than Tms-O-Tf in complex-ing the carbonyl group and allows for application of α,β-unsaturated esters like methyl crotonate or methyl acrylate in cycloaddition to various dienes, which are otherwise prone to decomposition. A wide variety of sensitive functional groups is tolerated by Tms-NTf2. Interestingly, the addition of fumarate (XVII) to diene (XIII) provides only trans-substituted cyclohexanones, while from maleate a mixture of cis- (XXI) and trans-adducts (XVIII)/(XIX) is obtained. — (MATHIEU, B.; GHOSEZ*, L.; Tetrahedron 58 (2002) 41, 8219-8226; Dep. Chim., Univ. Cathol. Louvain,B-1348 Louvain-la-Neuve, Belg.; Eng.) — Mischke

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2002 Cycloaddition reactions