An ab initio molecular orbital study on the magnesium controlled 1,3-cycloaddition of nitrile oxides and allylic alcohols with regio- and stereoselectivity

Ab initio molecular orbital calculations at the MP4(SDTQ)/6-31G*//RHF/6-31G * level of theory were used to obtain detailed insight into the reaction pr ofile on the Mg controlled 1,3-cycloaddition of nitriles oxide with allylic alcohols. It was confirmed that the complex formation reduces the HOMO-LUM O energy gaps of the two reactants. The propensity correlates well to calcu lated activation energies of the cycloaddition. The sm-stereoselectivity de pends on the steric repulsion between the vinyl fragment and the substituen t at the ct-position of the alcohol or alkoxide. THF or Et2O in the reactio n mixture prevent the coordination of (RCNO)-C-1 from forming the Mg interm ediate and result in deccelerating the cycloaddition. The results obtained in the present study well explain an important role of the Mg2+ ion in the 1,3-dipolar cycloadditions of nitrile oxides with allylic alcohols. (C) 200 0 Elsevier Science Ltd. All rights reserved.