PERI-, SITE-, AND REGIOSELECTIVITY IN HETEROCUMULENE-HETERODIENE CYCLOADDITION REACTIONS : AN AB INITIO STUDY OF THE SYSTEM KETENIMINE + ACROLEIN

Geometries of the 12 possible cycloaddition products between ketenimine and acrolein as well as of the respective transition states have been obtained by ab initio calculations at the MP2/6-31G* level. Energies were obtained up to the MP4(SDTQ)/6-31+G* level. On the basis of product stability arguments, addition of the ketenimine CC double bond is more favorable than reaction of the CN double bond. Similarly, acrolein also preferentially should react via its CC rather than CO bond. In kinetically controlled reactions, however, participation of the ketenimine CN bond in [4 + 2] cycloadditions across the oxa-1,3-dienic system is comparable to (8) or far more feasible than (7) reaction of the CC bond.