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.

Key words

iminium ion - Diels-Alder - cycloaddition

References and Notes

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13

The anti-methine endo adducts were identified as the lowest energy conformers on the basis of B3LYP/6-311G(d)optimization and frequency calculations which were performed using Chem3D^®.