IRON LEWIS-ACID CATALYZED CYCLOPROPANATION REACTIONS OF ETHYL DIAZOACETATE AND OLEFINS

The iron Lewis acid [(eta5-C5H5)Fe(CO)2(THF)]+BF4- (1) was observed to catalyze the decomposition of ethyl diazoacetate (EDA) with olefins t o form cyclopropanes. With styrene, EDA gave 68 +/- 3% of cyclopropane s with very high cis selectivity (85 +/- 3/15 +/- 3). To determine the potential utility of the catalyst, reactions with other olefins were investigated. Alpha-methylstyrene gave 60% of cyclopropane products wi th a cis/trans ratio of 60/40, and p-methylstyrene gave 66% of cyclopr opanes with a cis/trans ratio of 60/40. Electron-rich olefins also gav e good yields of cyclopropanes with somewhat lower selectivities (ethy l vinyl ether, 68 %, cis/trans 45/55; 2-methoxypropene, 66%, Z/E 55/45 ). The use of aliphatic olefins such as 2-methyl-2-butene and cyclohex ene yielded no cyclopropanation products. Despite the unsuccessful det ection of the iron carbene complex [(eta5-C5H5)(CO)2Fe=CH(CO2Et)]+ (6) via variable-temperature H-1 NMR, the formation of carbene dimer prod ucts (diethyl fumarate and diethyl maleate) and the selectivity in the cyclopropanation reaction has led us to suggest the involvement of 6 as an intermediate for the reaction.