Catalytic cyclopropanation of electron deficient alkenes mediated by chiral and achiral sulfides: scope and limitations in reactions involving phenyldiazomethane and ethyl diazoacetate

Phenyldiazomethane reacts with electron deficient alkenes in the presence o f catalytic amounts of transition metal catalyst [Rh-2(OAc)(4) was better t han Cu(acac)(2)] and catalytic amounts of sulfide to give cyclopropanes. Pe ntamethylene sulfide was found to be superior to tetrahydrothiophene and th e optimum solvent was toluene. Under these optimised conditions a range of enones were cyclopropanated in high yields. Cyclic enones and acrylates wer e not successful in this process. The use of the chiral 1,3-oxathiane deriv ed from camphorsulfonyl chloride in 2 steps in this process furnished cyclo propanes in good yield and very high enantiomeric excess (>97% ee). The abs olute stereochemistry of cyclopropane 10 was proven by X-ray analysis and t he origin of the stereochemical induction has been rationalised. Extension of this work to include diazoesters was partially successful. Again pentame thylene sulfide was found to be superior to tetrahydrothiophene, but this t ime both Rh-2(OAc)(4) and Cu(acac)(2) were found to be equally effective. E nones, fumarates and unsaturated nitro compounds worked well but simple acr ylates and unsaturated aldehydes were not effective substrates. Control exp eriments were conducted in which the stabilised ylide was isolated and reac ted with the less successful substrates and, whilst unsaturated aldehydes s till gave low yields, simple acrylates gave high yields of the correspondin g cyclopropane. The use of the chiral 1,3-oxathiane was not successful with these more stable diazo compounds.