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E n a n t i o s e l e c t i v e S y n t h e s i s o f M e t h y l t r a n s -C h r y s a n t h e m a t e

Samarium diiodide on one hand, diphosphorus tetraiodide, and phosphorus triiodide on the other, react with vinylcyclopropane epoxides to produce either allylic alcohols or vinylcyclopropanes resulting from cyclopropane ring-opening or deoxygenation of the epoxide, respectively.We recently described 1 that ethyl oxido-chrysanthemate 1a is not, as expected, deoxygenated to ethyl chrysanthemate 2a by samarium diiodide, 2a-e the 'Kagan reagent' 2f in the presence of tert-butyl alcohol, but instead mainly produces 3a resulting from cyclopropane ringopening (Scheme 1, Table 1, entry a).Scheme 1 Reaction of samarium diiodide with vinylcyclopropane epoxides bearing an ester or a phenyl group on the cyclopropane ring We therefore initiated a study aimed to understand the reasons which favor (i) the participation of the cyclopropane ring after the samarium diiodide initiated epoxide ring-opening, (ii) the regioselectivity of the cleavage of the cyclopropane ring.We first confirmed that the conditions used are mandatory for success and that the presence of tert-butyl alcohol (2.5 equiv) is strictly required. 3 Surprisingly, it neither takes place in the presence of HMPA or DMAE (dimethylaminoethanol) which are known to enhance the reducing ability of samarium diiodide. 2

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