Diastereoselective, photocatalytic [2 + 2] dimerizations of alkenylboronic acids promoted by sugar alcohols

In the presence of the sugar alcohol meso-erythritol, trans-2-arylvinylboronic acids undergo regio- and diastereoselective, photocatalytic [2 + 2] cycloadditions, generating all-trans-substituted cyclobutane-1,2-bis(boronic acid) derivatives. A covalent templating mechanism is proposed, involving in situ formation of a 2:1 boronic acid:tetraol adduct – likely a mixed boronic ester/hemiboronic ester. The protocol has been applied to various substituted trans-2-arylvinylboronic acid derivatives, providing access to chiral, C2-symmetric cyclobutane derivatives that would be challenging to synthesize by other means.