Difluoromethylene group introduction

The system dibromodifluoromethane/tris(diethylamino)phosphane can be used for the introduction of the difluoromethylene group in 3-oxo glucose derivatives. This process consists of initial formation of the multiple bond, e.g, in 27 the difluoromethyl group is available by reduction.204 205 Compounds containing the difluoromethyl group show high biological activity. 

The 3-difluoromethylenated counterpart 6a, on the other hand, was accessible by way of tin acetal-mediated regioselective benzoylation at 2 position (42,43), followed by the above-depicted PDC oxidation-difluoromethylene Wittig reaction processes. For introduction of a Cp2=C group at 4 position, after benzylidene acetal was cleaved and the resultant diol was regioselectively protected at 6 position by TBSCI, the routine oxidation-difluoromethylenation procedure yielded the desired compounds. 

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