Silva María A, Pellegrinet Silvina C, Goodman Jonathan M
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
J Org Chem. 2002 Nov 15;67(23):8203-9. doi: 10.1021/jo026324i.
The reactions of alkynyldihaloboranes and alkynyldialkylboranes with butadiene have been explored by using DFT methods at the B3LYP level with the 6-31G basis set. Transition structures for the concerted [4+2] cycloaddition have been found for the alkynylborane derivatives. Along with these, another reactive pathway has been found for the cycloaddition process with transition structures of high [4+3] character. The transition structures for the 1,4-alkynylboration processes have also been found. The geometries computed for the cycloaddition transition structure with high [4+3] character and the 1,4-alkynylboration transition structures are surprisingly similar though leading to different products. IRC calculations suggest that the [4+3] cycloaddition and alkynylboration pathways are associated by a zwitterionic structure.
