Asymmetric copper-catalyzed [2,3]-sigmatropic rearrangements of alkyl- andaryl-substituted allyl sulfides

The asymmetric copper-catalyzed generation and subsequent [2,3]-sigmatropic rearrangement of sulfur ylides is strongly dependent on the structure of t he starting allyl sulfide. A series of alkyl and aryl substituted allyl sul fides (2a-i) were reacted with ethyl diazoacetate in the presence of copper triflate (CuOTf) and a C-2-symmetric bis-oxazoline ligand (5a-c). The degr ee of asymmetric induction ranged from 2.8% for allyl methyl sulfide (2a) t o 60% for (1S,2S,5R)-(+)-allyl menthyl sulfide (2d). The enantioselectivity of the reactions was also dependent on the electronic nature of the sulfid e; allyl phenyl sulfide (2e) gave a 14% ee, whereas allyl p-methoxyphenyl s ulfide (2i) produced only an 8% ee. The stereochemistry of 2d and (1R,2S,5R )-(+)-allyl menthyl sulfide (7) was assigned on the basis of NMR spectrosco pic experiments.