Diastereoselective Reduction of α,α-Difluoro β-Hydroxy Ketones to syn- and anti-2,2-Difluoro-1,3-diols

While reduction of α,α-difluoro β-hydroxy ketones with diisobutylaluminium hydride gave a mixture of syn- and anti-diols in various ratios, the reduction in the presence of zinc bromide or zinc chloride-N,N,N′,N′-tetramethylethylenediamine was highly selective and gave syn-2,2-difruoro-1,3-diols predominantly, anti-2,2-Difluoro-1,3-diols were obtained by the reduction of α,α-difluoro β-hydroxy ketones with aluminium isopropoxide.