COMBINED AM1 MM3 COMPUTATIONS ON ORGANIC-SYSTEMS - THE DIELS-ALDER REACTION AS A TEST-CASE/

A combined AM1/MM3 method for computations in organic chemistry has be en implemented and applied to the study of Diels-Alder reactions using the localised self-consistent field approach. In the case of acrylic esters, we show that the O-R bond is adequate for separating the quant um and classical moieties. Results for the reaction-energy profile, Le wis-acid catalytic effect and diastereofacial selectivity are presente d. The agreement with full quantum computations is in general good. In addition, we show that AM1/MM3 computations overcome the well-known d eficiencies of semi-empirical core-core repulsion functions. (C) 1998 Elsevier Science B.V. All rights reserved.