Quantum mechanical calculation for determination of more stable isomer of phosphorous ylide involving an indole

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reactions between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH-acid, such as indole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. In the recent work, the stability of the Z- and the E- isomers were undertaken for the two rotamers of phosphorus ylides involving an indole [namely dimethyl 2-(indole-1-yl)-3-(triphenyl- phosphanylidene)- butanedioate(4a)] by means of atoms in molecules AIM, CHelpG and NBORead methods.