Trimethylsilyl bis(trifluoromethanesulfonyl)imide as a tolerant and environmentally benign Lewis acid catalyst of the Diels–Alder reaction

N-trimethylsilyl bis(trifluoromethanesulfonyl)imide (TMSNTf2) was readily prepared in situ by protodesilylation of trimethylsilane, allyl- or phenyltrimethylsilane with bis(trifluoromethylsulfonyl)imide. NMR studies showed that TMSNTf2 was much more effective than TMSOTf in complexing the carbonyl group of trans-methylcrotonate. As a result, TMSNTf2 was found to be superior to TMSOTf as a catalyst for the Diels–Alder reaction of α,β-unsaturated esters with a wide variety of dienes. In contrast to many metal derived Lewis acids, TMSNTf2 was found tolerant of many sensitive functional groups present in the diene partner.