An efficient and scalable synthesis of an antidiabetic drug, tofogliflozin (1), which was identified as a highly selective sodium glucose cotransporter 2 (SGLT2) inhibitor, is described. A key factor in the synthesis of 1 was the selection of the purpose-designed protecting group, which plays a strategic role in protection, chemoselective activation, and crystalline purification. The developed and optimized method made it possible to prepare 1 on a multidecagram scale without any column chromatography.
The alpha,alpha-gem-difluorination of 2',4'-difluoro-alpha-(methylthio)acetophenone (1a) with N-fluoropyridinium salts gave 2',4',alpha,alpha-tetrafluoro-alpha-(methylthio)acetophenone (3a). This reaction was accelerated by the addition of zinc chloride, zinc bromide or anhydrous iron(III) chloride, and higher yields than the reaction without additives were obtained. The gem-difluorination reaction using FP-T300 in the presence of zinc bromide was applicable to other alpha-(alkylthio)acetophenone derivatives (1).
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