Recent advances in sustainable organic transformations using methanol: expanding the scope of hydrogen-borrowing catalysis

The present review focuses on recent progress achieved from 2017 to March 2021 using methanol as a C1-alkylating agent. A series of novel metal-catalyzed hydrogen-borrowing processes has been developed using methanol. Most importantly, the non-precious-metal-catalyzed activation and functionalization of methanol are discussed in detail, including mechanistic investigations. The design of interesting pincer complexes for the conceptual activation of methanol, which holds great potential, is covered. Furthermore, the methylation of nitroarenes or alkanes and the upgrading of methanol to higher-order alcohols, including Guerbet-type transformations and beta-alkylations using molecularly defined catalysts, are discussed. Recently reported C, N, and O methylations will be covered, including ketone alkylations (alpha or beta), N-formylations, amidations, and sulfonylations, as well as other interesting areas. The exciting applications of industrially important heterogeneous catalysts and their application in methanol activation are covered. The synthesis of various important drugs having a "-CH3" motif and late-stage methylation, including the incorporation of the medicinally useful "-CD3" motif, are interesting additions to the present discussions. Photo- and electro-catalytic transformations using methanol will also be discussed. The limited number of review articles covering this subject area has limited its understanding; therefore, we believe that this updated review article is necessary to focus the attention of researchers in this direction.