Novel Use of N-Carboalkoxy α,β-Unsaturated Iminium Ions as Dienophiles in Diels-Alder Reactions

Abstract

Tricyclic spiro-N,O-acetals have been assembled in a single step by cycloaddition of hydroxymethyl-substituted dienes to iminium ion activated dienophiles that were generated by acidolysis of α,β-unsaturated-N-carboalkoxy-N,O-acetals or β-methoxymethyl-N-carboalkoxy-enamines. The cycloaddition was conducted using Sc(OTf)3 as a mild Lewis acid affording the endo adducts in moderate yields.