VILSMEIER-HAACK: formylation of 2,3-diphenylbenzofuran (la) gave the 5,6-diformyl derivative (lb). Huang-Minlon reduction of lb yielded the 5,6-dimethyl derivative (1c). Oxidation of 1c followed by hydrolysis the 2-hydroxy-4,5-dimethylbenzophenone (2b) was obtained.
Condensation of lb with primary amines gave the corresponding Schiff bases (3 a-j).
1a on bromination gave 5-bromo-2,3-diphenylbenzofuran (1 d), which on hydrolysis via oxidation yielded 2-hydroxy-5-bromobenzophenone (2 d). 1d was also obtained by condensation of benzoin and p-bromophenol in presence of sulphuric acid.
Conrad-Limpach reaction of 5-methoxy-6-amino-2,3-diphenylbenzofuran (1e) and ethyl acetoacetate gave 2,3-diphenyl-7-methyl-5-methoxy-9-hydroxy[2,3-f]furoquinoline via the azomethine (4).
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