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A Highly Diastereoselective Synthesis of (1R)-(+)-Camphor-Based Chiral Allenes and Their Asymmetric Hydroboration−Oxidation Reactions

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journal contribution
posted on 25.01.2002, 00:00 authored by Shang-Cheng Hung, Yen-Fang Wen, Jia-Wen Chang, Chun-Chen Liao, Biing-Jiun Uang
Synthesis of camphor derived chiral allenes and their hydroboration−oxidation reactions are described. Reaction of (1R)-(+)-camphor with alkynyllithium followed by the reduction of the resulted propargyl alcohol derivatives using AlH3 furnished chiral allenes 2ag in excellent yields with high diastereoselectivity. Reduction of the propargyl alcohols with aluminum hydride proceeded through selective intermolecular anti-addition of hydride ion. The stereochemistry of the chiral allenes 2 was assigned based on lanthanide shift studies and chemical correlations. Diastereoselectivity was observed in the hydroboration−oxidation of 2 which produced a mixture of (E,R) and (E,S) stereoisomers in a ratio of 6:1 to 18:1.