Dehydrohalogenation Reactions Using Hindered Lithium Dialkylamide Bases

Abstract The E2 eliminations of 2-substituted butanes with a series of hindered lithium dialkylamide bases has been exmined. Excellent yields of butenes are obtained using 2-bromobutane and 2-iodobutane. Alkyl chlorides, acetates and tosylates give poor yields of olefin product. Elimination reactions show a rise, then a fall, in the 1-butene/2-butene(s) product ratio as the amide bulk increases. Dehydrohalogenation of 2-bromobutane with lithium 2,2,6,6-tetramethylpiperidide in the presence of one equivalent of 12-crown-4 gives 1-butene/2-butene(s) product ratio of 99:1.