Advances in the Synthesis of Methylated Products through Indirect Approaches

Abstract

AbstractMethylation is a well‐known structural modification in organic and medicinal chemistry. In addition to using conventional methylation reagents for direct methylation, indirect methylation approaches have been also successfully applied, particularly to tackle the isolation difficulty among the methylated product, the unreacted starting material, and the dimethylated by‐product due to the structural similarities between them. This review summarizes recent advances in the synthesis of methylated products through indirect approaches – transforming functionalized intermediates into the methylated products. The indirect methodologies surveyed in this review are useful for chemists to select appropriate methylation strategies, particularly for the challenging synthesis of methylated products at a large scale in drug discovery.Abbreviations: AIBN: azobisisobutyronitrile; Cbz: carbobenzyloxy; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DIBAL: diisobutylaluminium hydride; FA: formic acid; Fmoc: fluorenylmethyloxycarbonyl; KOTMS: potassium trimethylsilanolate; LAH: lithium aluminium hydride; LiHBEt3: lithium triethylborohydride; PC: photocatalyst; PMHS: polymethylhydrosiloxane; PSMS: zinc bis(phenylsulfonylmethanesulfinate); SAM: S‐adenosylmethionine; SET: single electron transfer; TBAF: tetra‐n‐butylammonium fluoride; TBS: tert‐butyldimethylsilyl; TEA: trimethylamine; TFA: trifluoroacetic acid; TMS: trimethylsilyl; Ts: 4‐toluenesulfonyl.magnified image