Triacetoxyborohydride → Methyl 7-((3-(tert-butoxycarbonyl)azetidin-1-yl)methyl)-4,5-dihydronaphtho[2,1-d]isoxazole-3-carboxylate

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Reaction Steps

To a solution of methyl 7-formyl-4,5-dihydronaphtho[2,1-d]isoxazole-3-carboxylate (Preparation 45C, 72 mg, 0.280 mmol) in methanol (5 mL) and 1,2-dichloroethane (1 mL) was added acetic acid (0.1 mL) and tert-butyl azetidine-3-carboxylate acetic acid salt (73.0 mg, 0.336 mmol). The contents were allowed to stir at room temperature for 40 min. and then sodium triacetoxyborohydride (178 mg, 0.840 mmol) was added. The reaction mixture was allowed to stir at room temperature overnight. Additional sodium triacetoxyborohydride (2 eq) was added and the reaction mixture was allowed to stir at room temperature for 2 hours. Additional sodium triacetoxyborohydride (4 eq) was added and the reaction mixture was allowed to stir at room temperature for 3 days. Additional amine (0.5 eq.), followed by additional triacetoxyborohydride (3 eq.) was added and the reaction mixtures was stirred at room temperature for 6 more hours to drive the reaction to about 90% conversion. The solvents were evaporated and the residue was re-dissolved into 80 ml ethyl acetate, washed twice with sat. sodium bicarbonate, dried over sodium sulfate, and concentrated to give 95 mg of product. The compound had an HPLC ret. time=0.75/2.0 min. (condition E); MS:(M+H)=399.3.

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