Weak intramolecular interactions as controlling factors in the diastereoselective formation of 3-phosphinoxido- and 3-phosphono-1,2,3,6-tetrahydrophosphinine 1-oxides

A series of 3-phosphinoxido-and 3-phosphono-1,2,3,6-tetrahydrophosphinine oxides was synthesized by the diastereoselective addition of diphenylphosphine oxide and dialkyl phosphites to the α,β-double-bond of 1,2-dihydrophosphinine oxides. Further refunctionalizations led to a 3-P(O)(OH)2 derivative and to a disulfide. The conformation of the products was evaluated using the B3LYP/6-31+G∗//B3LYP/3-21G∗ method, validated by calculation for a simple tetrahydrophosphinine oxide with a known stereostructure. The preferred conformers of the 3-P(X)Z2-tetrahydrophosphinine derivatives were among the twist-boat forms containing the exocyclic P-function in the axial position due to three kinds of favorable intramolecular interactions. Only the 3-P(O)(OH)2 derivative was found to adopt a half-chair conformation as a consequence of intramolecular H-bonding.