Reinvestigation of a criticized mechanistic probe study of metal hydride reductions of alkyl halides
摘要:
Published claims that LiAlH4 promotes isomerizations of either 7-iodo-2-methoxy-2-heptenenitrile (1) or 2-methoxy-2-heptenenitrile (2) and the speculations resulting from these claims have led to new studies of reactions of 1 and 2. Highly isomerically enriched samples of 1 and 2 were prepared, and the equilibrium populations of isomers for both 1 and 2 were determined by iodine-mediated equilibrations. Reactions of isomerically enriched samples of 1 and 2 as well as mixtures of isomers with LiAlH4 demonstrated that LiAlH4-induced isomerizations did not occur. Absolute yields of product 2 from reactions of 1 with limited amounts of LiAlH4 did not agree with previously reported results. Reactions of 2 with limited amounts of LiAlH4 resulted in selective destruction of 2 with (Z)-2 reacting faster than (E)-2. On the basis of these facts and the fact that speculations regarding radical intermediates from reactions of 1 with LiAlH4 are inconsistent with known kinetic values for radical reactions, the published criticisms of a study employing 1 as a probe for radical formation in reactions with metal hydrides are found to be without merit.
Reinvestigation of a criticized mechanistic probe study of metal hydride reductions of alkyl halides
摘要:
Published claims that LiAlH4 promotes isomerizations of either 7-iodo-2-methoxy-2-heptenenitrile (1) or 2-methoxy-2-heptenenitrile (2) and the speculations resulting from these claims have led to new studies of reactions of 1 and 2. Highly isomerically enriched samples of 1 and 2 were prepared, and the equilibrium populations of isomers for both 1 and 2 were determined by iodine-mediated equilibrations. Reactions of isomerically enriched samples of 1 and 2 as well as mixtures of isomers with LiAlH4 demonstrated that LiAlH4-induced isomerizations did not occur. Absolute yields of product 2 from reactions of 1 with limited amounts of LiAlH4 did not agree with previously reported results. Reactions of 2 with limited amounts of LiAlH4 resulted in selective destruction of 2 with (Z)-2 reacting faster than (E)-2. On the basis of these facts and the fact that speculations regarding radical intermediates from reactions of 1 with LiAlH4 are inconsistent with known kinetic values for radical reactions, the published criticisms of a study employing 1 as a probe for radical formation in reactions with metal hydrides are found to be without merit.