Reactions of grignard reagents with bis- or mono-phosphonium ions in situ generated from Bu3P and dicarboxylic acid dichlorides or omega-ethoxycarbonyl alkanoyl chlorides as a novel method to obtain diketones and ketoesters.

Abstract

Reactions of Grignard reagents with bis-phosphonium or mono-phosphonium ions in situ generated from BusP and ClCO(CH2)nCOCl (5) or ClCO(CH2)nCO2Et (13) as a tool for preparation of symmetrical diketones or ketoesters were examined. Addition of Bu3P (2.0 eq) to a THF solution of 5 (n=2) at -40 degrees C followed by addition of n-BuMgCl (2.0 eq) gave the corresponding diketone in good yield. When a mixture of BusP and the Grignard reagent (2.0 eq each) was added to the dichloride solution at the same temperature, a better result was obtained. The latter method not with PhMgBr but with n-BuMgCl or MeMgBr was shown to be useful for preparation of symmetrical alkanediones and keto alkanoates from various 5 (n=2-6) and 13 (n=2 or 3), respectively. For synthesis of alpha-diketones or alpha-ketoesters, only PhMgBr entered the reaction, although the yields were not satisfactory. Addition of a mixture of Bu3P (2.0 eq), MeMgBr (1.0 eq) and BuMgCl (1.0 eq) to a THF solution of 5 (n=4) at -40 degrees C afforded a mixture of 2,7-undecanedione and the corresponding two symmetrical diketones, with the yield of the unsymmetrical diketone being 36%.