Multifold Bond Cleavage and Formation between MeOH and Quinoxalines (or Benzothiazoles): Synthesis of Carbaldehyde Dimethyl Acetals

A K2S2O8-mediated direct
cross-coupling of quinoxalines (or benzothiazoles) with methanol leading
to 2-quinoxalinyl (or 2-benzothiazolyl) carbaldehyde dimethyl acetals
has been achieved. 2-Quinoxalinyl carbaldehyde dimethyl acetals were
readily converted into 2-quinoxalinyl carbaldehydes in good to excellent
yields under acidic conditions. Preliminary mechanistic studies suggest
that the reaction proceeds via multifold bond cleavage and formation
between methanol and N-heterocycles involving a dioxygen-participated
radical process. This method allows for the synthesis of a variety
of 2-quinoxalinyl (or 2-benzothiazolyl) carbaldehyde dimethyl acetals
directly via cross-coupling of simple N-heterocyclic
C–H bond and methanol under aldehyde-, acid-, and transition-metal-free
conditions.