SYNTHESIS OF ISOMERIC CAGE-FUNCTIONALIZED DIACYL-FUROXANS AND THEIR SUBSEQUENT THERMOLYTIC FISSION TO AN ACYL NITRILE OXIDE

A three step synthesis of a mixture of isomeric cage-functionalized fu roxans (4) is described. When heated in the presence of ethyl propiola te, furoxans (4) undergo cycloreversion to afford two equivalents of t he corresponding acyl nitrile oxide (5) which is trapped in situ by et hyl propiolate. The trapping reaction proceeds via a highly regioselec tive [3 + 2] cycloaddition to produce 6 (61% yield), whose structure w as established unequivocally via application of X-Ray crystallographic methods. The observed regioselectivity of the [3 + 2] cycloaddition p rocess is rationalized via frontier molecular orbital analysis by usin g semiempirical MO calculations (AM1 Hamiltonian) and at the HF/3-21G level of theory.