Interaction of sulfinimines with boron trifluoride. A theoretical study

Calculations using B3PW91 and MP2 methods were performed on possible complexes of sulfinimine MeS(O)NCHMe with BF3 to distinguish the site of interaction. The energy calculations exclude formation of the complex at the sulfur atom but not at the nitrogen or oxygen atoms. DFT calculations of chemical shifts show remarkable influence on the nitrogen shielding in the complex at the oxygen atom. The lowest energy conformation of the sulfinimine-BF3 complex explains the high stereoselectivity observed in reactions of sulfinimines with nucleophiles in the presence of boron Lewis acids.