1,1,1-Trimethoxy-2-methylpropane → 4,5-dihydro-3-methyl-2-(1-methylethyl)-4-(2-thienyl)-3H-1,3-benzodiazepine

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A stirred solution of 3.45 g of 2-amino-N-methyl-α-(2-thienyl)benzeneethaneamine and 13.34 g of trimethyl orthoisobutyrate was treated rapidly with 3.8 ml of glacial acetic acid. The reaction mixture was refluxed for 8 hours and cooled to room temperature overnight. The mixture was concentrated on a rotary evaporator at 70° C. After standing overnight under refrigeration, the residue was dissolved in 60 ml of 10% hydrochloric acid solution and extracted with diethyl ether (2×50 ml). The aqueous phase was basified with 10% sodium hydroxide solution and extracted with dichloromethane (2×75 ml). The combined organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated to an oil. The oil was purified by HPLC (Water's Associates Prep LC/System 500; silica gel; sample applied in dichloromethane; methanol as eluent). Concentration of the appropriate fractions yielded 1.08 g of 4,5-dihydro-3-methyl-2-(1-methylethyl)-4-(2-thienyl)-3H-1,3-benzodiazepine as an oil.

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