Alkylation of a chiral hydrazone by means of asymmetric addition of Grignard reagents to the carbon-nitrogen double bond.
Hiroshi TakahashiInstitute of Medicinal Chemistry, Hoshi University, Kaken Pharmaceutical Co., LtdYuji SuzukiInstitute of Medicinal Chemistry, Hoshi University, Kaken Pharmaceutical Co., Ltd
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A chiral hydrazone, (E)-(S)-N'-benzylidene-N, 3-dimethyl-2-hydrazinobutanol (6), was synthesized from (S)-valinol. Compound 6 was reacted with Grignard reagents to give optically pure (2S, 1'S)-N, 3-dimethyl-N'-1'-phenylalkyl-2-hydrazinobutanols (7a and 7b). However, N'-2'-aryl-1'-phenylethyl-N, 3-dimethyl-2-hydrazinobutanols (7c and 7d) were each obtained as a mixture of two diastereomers. Nitrogen-nitrogen bonds of 7a and 7b were cleaved by hydrogenolysis to give (S)-1-phenylalkylamines (8a and 8b), and their absolute configurations and optical purities were confirmed. These reactions were assumed to proceed via the chelated sixmembered ring intermediates.
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