Direct Access to Monoprotected Homoallylic 1,2-Diols via Dual Chromium/Photoredox Catalysis

Herein, we present
a dual catalytic strategy to efficiently obtain
monoprotected homoallylic 1,2-diols by coupling abundant aldehydes
with simple (silyl) enol ethers, thus providing direct access to this
important motif without the (super) stoichiometric use of prefunctionalized
metal-allyl species. The modularity of our approach is shown by the
introduction of several silyl- and alkyl-based protecting groups.
To highlight functional group tolerance and chemoselectivity, we demonstrate
the functionalization of a variety of aliphatic and (hetero)­aromatic
aldehydes, even in the presence of ketones and esters. Mechanistic
studies support a radical mechanism, starting from the single electron
oxidation of the enol ether.