Boron-Templated Dimerization of Allylic Alcohols To Form Protected 1,3-Diols via Acid Catalysis

Abstract

We report an unprecedented boron-templated dimerization of allylic alcohols that generates a 1,3-diol product with two stereogenic centers in high yield and diastereoselectivity. This acid-catalyzed reaction is achieved via in situ formation of a boronic ester intermediate that facilitates selective cyclization and formation of a cyclic boronic ester product. High yields are observed with a variety of allylic alcohols, and mechanistic studies confirm the role of boron as a template for the reaction.

Emergent Organoboron Acid Catalysts

“…Boronic acid mediated carbocation formation was also reported in the dimerization of allylic alcohols reported by the Michaelis group (Scheme 30). 117 In this case, the phenylboronic acid acts as a template to organize the allylic alcohols as boronic esters. Catalytic triflic acid or copper(II) then activates one alcohol in tandem with the boronic acid, inducing formation of a cation that reacts rapidly with the other molecule of allylic alcohol, forming a 1,3-diol with high diastereoselectivity.…”

Regioselective Cycloaddition and Substitution Reaction of Tertiary Propargylic Alcohols and Heteroareneboronic Acids via Acid Catalysis

“…Subsequently, the tetracoordinate boronate C undergoes an intramolecular deborylative migration to yield the desired product 3p . In the presence of a Brønsted acid ( 4f ), the propargylic alcohol and 2a in situ generate the boronic ester that is protonated by acid to E , which is attacked by the 3-position of 2a to form allene B and then undergoes deborylative migration to yield product 3p . Because of the electrophilic site shift and the high steric hindrance at the α-position of alcohol, the reaction of γ-alkyl propargyl alcohols with 2a could not proceed with 4a as catalyst (for DFT calculations, see the Supporting Information).…”