sulfuric acid in N,N-dimethyl-formamide 1 h, 150°C, stirring (2 h); extraction (CH2Cl2), washing (aq NaHCO3, brine), evapn., chromy. (silicagel, hexane-benzene);

sulfuric acid in N,N-dimethyl-formamide addition (1 h, 140°C), stirring (5 h); extraction (CH2Cl2), washing (aq NaHCO3, brine), evapn., chromy. (silicagel, hexane-CH2Cl2);

sulfuric acid in N,N-dimethyl-formamide addition (1 h, 150°C), stirring (2 h); extraction (CH2Cl2), washing (aq NaHCO3, brine), evapn., chromy. (silicagel, hexane-CH2Cl2); anal. H(1) NMR;