General and practical approach to the syntheses of linear homoallylic alcohols*
Hin-Soon Cheng and Teck-Peng Loh
Division of Chemistry and Biological Chemistry, Nanyang Technological University, Singapore 637616, Republic of Singapore
Abstract: We have demonstrated that metal-mediated allylation of aldehydes can afford γ‑homoallylic alcohols or α-linear homoallylic alcohols by judicious choice of the solvents. A new mechanism has been proposed to account for this new α-selective metal-mediated allylation reaction. On the other hand, the metal-mediated prenylation under the same conditions to obtain α-prenyl alcohols was unsuccessful. Detailed mechanistic studies have resulted in the discovery of a new method to obtain compounds with diverse structures via an oxonium-ene cyclization. Suppressing the oxonium-ene reaction during the reaction has resulted in the formation of α-prenyl alcohols. A highly enantioselective process to obtain α‑prenyl product in high optical purity has also been accomplished.
Keywords: Homoallylic alcohols; metal-mediated allylation; prenylation; α-selectivity; oxonium-ene cyclization.
*An issue of reviews and research papers based on lectures presented at the 15th International Conference on Organic Synthesis (ICOS-15), held in Nagoya, Japan, 1-6 August 2004, on the theme of organic synthesis. Other presentations are published in this issue, pp. 1087-1296.