Diastereoselective SmI2-Mediated 3-exo-trig Cyclisation of (delta)-Oxo-Alkylidenemalonates to Cyclopropanols

In the presence of samarium diiodide and a proton donor (tert-butanol or phenol). (delta)-oxo-(gamma).(gamma)-disubstituted-alkylidenemalonates readily cyclise according to the 3-exo-trig mode to give. depending on the exact nature of the substrate, tram and cis cyclopropanols or lactones derived from the cis isomers. Total stereoselectivity towards the formation of trans cyclopropanols is observed with di-tert-butyl alkylidenemalonates when PhOH is used as the protonating agent.