Asymmetric Intramolecular Hydroalkoxylation of 2‐Vinylbenzyl Alcohols with Chiral Boro‐Phosphates

Abstract Asymmetric intramolecular hydroalkoxylation of alkenes represents a very important approach to access optically active cyclic ethers. It was found that B(C 6 F 5 ) 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.