REGIOSELECTIVE AND ENANTIOSELECTIVE SUBSTITUTION OF ACYCLIC ALLYLIC SULFOXIMINES WITH BUTYLCOPPER IN THE PRESENCE OF LITHIUM IODIDE AND BORON-TRIFLUORIDE

Enantiomerically pure N-methyl-, N-benzyl-, and N-(methoxyethyl)-S-(ph enyl)cinnamylsulfoximines as well as the corresponding crotylsulfoximi nes have been prepared from N-methyl-, N-benzyl-, and N-(methoxyethyl) -S-(lithiomethyl)sulfoximines and carbonyl compounds by an addition-el imination-isomerization reaction sequence. Under basic conditions, com plete isomerization of the vinylic sulfoximines, obtained as intermedi ates, to the corresponding allylic sulfoximines takes place. Chromatog raphically separable mixtures of (E) and (Z) allylic sulfoximines were isolated in the case of beta,gamma-disubstituted allylic sulfoximines . The (E/Z) ratio depends on the nature of the substituents in the bet a- and gamma-positions, and the equilibrium amount of the (Z) isomer v aries from 68% to nil. The allylic N-methylsulfoximines do not racemiz e thermally, and their rearrangement to the corresponding allylic sulf inamides is negligible. Upon prolonged treatment with boron trifluorid e at low temperatures allylic N-methylsulfoximines are recovered uncha nged. The crystal structure of aphthalen-2-ylmethyl)-N-methyl-S-phenyl sulfoximine was determined. Reaction of the allylic sulfoximines with butylcopper in the presence of lithium iodide and boron trifluoride le ads with very high gamma-selectivities and moderate to high enantiosel ectivities to the corresponding chiral alkenes. Their configuration wa s determined by chemical correlation through ozonolysis to the corresp onding carbonyl compounds. The asymmetric induction exerted by the chi ral N-methyl-S-phenylsulfoximine group strongly depends on the double bond configuration and the substituents in the beta- and gamma-positio ns. The (E) allylic sulfoximines are substituted with low to moderate enantioselectivities (2-66%), whereas the (Z) allylic sulfoximines rea ct with much higher enantioselectivities (69-92%). Interestingly, subs titution of the beta-methyl-gamma-phenyl-substituted (Z) allylic sulfo ximine and its beta-phenyl-gamma-methyl isomer proceeded with almost t he same degree of asymmetric induction but with the opposite sense. Re placement of the N-methyl group by a benzyl or a methoxyethyl group ha s no significant influence on the regio- and enantioselectivity of the substitution.