Cl.[CH3:2][NH:3][C:4]1([C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)[CH2:13][CH2:12][C:7]2(OCC[O:8]2)[CH2:6][CH2:5]1>O>[CH3:2][NH:3][C:4]1([C:14]2[CH:15]=[CH:16][CH:17]=[CH:18][CH:19]=2)[CH2:13][CH2:12][C:7](=[O:8])[CH2:6][CH2:5]1A mixture of conc. HCl (15 ml) and water (8 ml) was poured over methyl-(8-phenyl-1,4-dioxaspiro[4.5]dec-8-yl)amine (2.1 g, 8.4 mmole) and the mixture was stirred for 5 days at RT. The reaction mixture was worked up by dilution with water (20 ml) and extraction with ether (3×30 ml). The ethereal phase was discarded. The aqueous phase was then made alkaline with 2N NaOH and extracted with dichloromethane (3×30 ml). The organic phase thereby obtained was dried over Na2SO4 and then concentrated by evaporation on a rotary evaporator. The ketone Ket-3 was obtained by chromatographic purification on silica gel with ethyl acetate/ethanol (4:1) in a yield of 1.38 g (81%) as a solid with a melting point of 32°-38° C.
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