Computational studies on the BF3-catalyzed cycloaddition of furan with methyl vinyl ketone: A new look at Lewis acid catalysis

Transition structures for both uncatalyzed and BF3-catalyzed Diels-Alder re actions involving furan and methyl vinyl ketone have been determined at the hybrid DFT (B3LYP/6-31G*) level of theory. The transition structures are p redicted to be relatively concerted and highly asynchronous in all cases. A subsequent bond-order analysis has been carried- out at the MP2/6-31G8//B3 LYP/6-31G*. The role of the Lewis acid and the origin of the endo selectivi ty have been discussed in terms of the nature and number of interactions pr esent in the four possible transition structures. The partition of the pote ntial energy barrier has also been used to estimate the contributions of th e pure deformation energy and the differential interaction between the reac tion partners on passing from the ground state to the saddle point. This an alysis reveals that the major influence arises from the heteradiene-dienoph ile interaction: instead of that corresponding to a BF8-dienophile interact ion.