Cesium carbonate → (1H-Thieno[3,2-c]pyrazol-5-yl)methanol

Participants

Reaction Conditions

Reaction Steps

To a solution of N-benzhydrylidene-N′-[1-[3-bromo-5-(tert-butyl-dimethyl-silanyloxymethyl)-thiophen-2-yl]-methylidene]-hydrazine [41.2 g, 80.2 mmol, Intermediate (69)] in toluene (500 mL) were added benzophenone hydrazone (18.9 g, 96.2 mmol), cesium carbonate (44.3 g, 136.3 mmol) then 1,1′-diphenylphosphinoferrocene (6.66 g, 12 mmol), and palladium acetate (1.35 g, 6 mmol). The orange mixture was stirred at 90° C. for 20 hours. The insoluble was filtered off and the filtrate was concentrated. The residue was chromatographed (n-heptane/ethyl acetate, 90/10). The resulting dark orange oil (45.7 g) was dissolved in ethanol (400 mL), then concentrated hydrochloric acid (150 mL) was added. The dark red mixture was stirred at 75° C. overnight. A 2.5 N solution of sodium hydroxide in water was added until pH is neutral. The mixture was then extracted twice with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated. The residue was chromatographed through silica gel (n-heptane/ethyl acetate, 50/50 then 20/80 as eluant) to afford (1H-thieno[3,2-c]pyrazol-5-yl)-methanol [3.3 g, 27%, Intermediate (70)] as an orange powder.

Provenance & Evidence