The reaction of 1,1-dibromocyclopropanecarboxamides with methyllithium

Abstract

On reaction with one equivalent of methyl-lithium at below –60 °C followed by aqueous quenching, the dibromoamides (5) and (6) were reduced to monobromides (10) and (9). An intermediate could be partially trapped as a mono-deuteride (15) by quenching with D₂O at low temperature, or as (14) by addition of benzadehyde, but could not be trapped by addition of Me₃SiCl or CO₂; however, quenching with D₂O after the reaction solution had been warmed to 35 °C led to (10) with no deuterium incorporation. The source of the proton in this last reaction was the solvent, ether. Treatment of (5) with 2 mol equiv. MeLi at –60 °C also led after low-temperature aqueous quenching to (10); if the temperature was rapidly raised to 35 °C two products, (20)(major) and (19)(minor), were isolated after quenching. If, however, (5) was treated with 1 mol equiv. MeLi at –60 °C, followed by very slow addition of a second mol equiv. at 35°, (19) was the major product. The monobromide (10) is an intermediate in both these reactions, and indeed leads to (19) and (20) in similar proportions to those from (5) when treated with 1 equiv. MeLi either rapidly or dropwise at 25–35 °C; reaction of (9) with 1 equiv. MeLi leads, however, to the ketone (11; X = Me).