CYCLOPROPANE HYDROCARBONS FROM gamma-BROMOETHERS¹

Abstract

The synthesis of olefins by the de-alkoxybromination of beta-bromoethers with zinc in aqueous ethanol is a well known and highly developed reaction (1). Adaptation of the method to the preparation of cyclopropane hydrocarbons by the de-alkoxybromination from gamma-bromoethers has barely been tried.Wolkoff and Menschutkin (2) treated 1-ethoxy-3-bromopropane (ethyl ybromopropyl ether) with zinc dust in 96 % alcohol, and upon warming the reaction mixture to 60-70' obtained an '(almost theoretical yield" of propylene. Paul (3) treated 1-phenoxy-3-iodopropane with magnesium in dry butyl ether and obtained an ('abondant degagement" (copious evolution) of cyclopropane. He also attempted to prepare cyclopropane from 1-ethoxy-3-chloropropane by this method, but obtained none; reaction conditions were not specified. Hammonet (4) prepared Grignard reagents from many of the higher bromoethers, but made no attempt to convert them into the corresponding hydrocarbons.It may be said that, in general, far less work has been reported on methods of synthesis for mono-alkylcyclopropanes than for polyalkylcyclopropanes. In the course of the present research we have developed what appears to be a general method for the preparation of mono-alkylcyclopropanes by the de-alkoxybromination of ybromoethers with magnesium; the scheme of synthesis starts with the commercially available 3-ethoxypropionaldehyde (see equations 1-111). It was also found that cyclopropane, itself, and polyalkylcyclopropanes can be prepared in three steps (equations IV-VI) from appropriate homologs of trimethylene glycol.In the preparation of the mono-alkylcyclopropanes, 3-ethoxypropionaldehyde was condensed with a Grignard reagent to produce a y-hydroxyether, from which the corresponding ybromoether was prepared by reaction with phosphorus tribromide. I CzHsOCHzCHzCHO + RMgX + CzHsOCHzCH2CH(OH)R I1 3CzHsOCHzCH2CH(OH)R + PBrs -+ 3C2HsOCH2CHzCH(Br)R Br 1