Reactivity and endo-exo selectivity in Diels-Alder reaction of o-quinodimethanes. An experimental and DFT computational study

endo-exo Selectivity in Diels-Alder cycloadditions of several o-quinodimeth anes (1-4) with acrylonitrile, 2-(5H)-furanone and N-methylmaleimide has be en investigated in acetonitrile solution. Transition structures of the cycl oaddition of the parent o-QDM (1), (E,E)1,8-dimethyl-o-QDM (2), isoindene ( 3) and 2,3-dihydronaphthalene (4) with acrylonitrile and maleimide were loc ated at both HF/6-31G* and B3LYP/6-31G* methods. Theoretical data reproduce fairly well both experimental absolute reaction rates and diastereoisomer ratios. The high endo selectivity has been rationalized mainly as a result of solvation effects (acetonitrile, PCM model) and reactant deformations. T he latter is due to steric interactions. (C) 2000 Elsevier Science Ltd. All rights reserved.