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Asymmetric Intramolecular Hydroalkoxylation of 2-Vinylbenzyl Alcohols with Chiral Boro-Phosphates
Caifang Han1,2, Wei Meng1,2, Xiangqing Feng1,2
1Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
Abstract:
Asymmetric intramolecular hydroalkoxylation of alkenes represents a very important approach to access optically active cyclic ethers. It was found that B(C6 F5 )3 could catalyze the cyclization of 2-vinylbenzyl alcohols with only 0.05 mol % catalyst loading, affording the desired product in high yields. To accomplish the asymmetric reaction, a novel type of chiral boro-phosphates was developed by treating chiral phosphoric acid with Piers' borane, in which the oxygen atom of P=O and the boron atom act as Lewis base and acid centers, respectively. A highly enantioselective hydroalkoxylation was successfully realized to give optically active 1,3-dihydroisobenzofuran derivatives in 78-99 % yields with 60-97 % ee's, in which an activation of O-H bond of alcohols by the boro-phosphate species is hypothesized.
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