LAUSR

Abstract The diastereoselectivity of cyclopropanations of styrene and α-fluorostyrene with diazoacetate depends on the catalyst used and the presence or absence of the fluorine substituent. The Cu(acac) 2 catalyzed reaction of styrene with diazoacetate led to 3:1 selectivity in favor of trans -2-phenylcyclopropane carboxylate, while α-fluorostyrene gave a 1:1 mixture of cis/trans -isomers. A competition experiment proved that α-fluorostyrene reacted slower compared to styrene itself. With the bulkier tetraphenyl-iron(III)-porphyrin chloride as catalyst, 10:1 or 3:1 mixture, respectively, were obtained. An advantage of the latter protocol is the in situ formation of ethyl diazoacetate from ethyl glycinate hydrochloride in aqueous solution by diazotation avoiding the in-substance application of the potentially explosive ethyl diazoacetate. Accordingly, a series of diastereoisomeric ethyl 2-aryl-2-fluoro-cyclopropane carboxylates was synthesized from p - or m -substituted α-fluorostyrenes.