Conformational analysis of 4h-1,3,2-benzodioxaphosphorin 2-sulfides with ab initio molecular orbital calculations

Among some 2-substituted 4H-1,3,2-benzodioxaphosphorin 2-sulfides, the 2-OMe derivative has the sulfur atom mainly in the quasiequatorial position. On the other hand, the conformation in which the sulfur is quasiaxial is favored in the 2-NHMe and 2-Et derivatives. We have done ab initio molecular orbital calculations for the model compounds, and such a substituent effect was reproduced. Moreover, the effect was discussed in terms of the intramolecular electrostatic interactions and the degree of charge distribution.