3,4,3 ,4 -Tetramethoxy-6- benzophenone

N.B. A mixture of products is obtained from aluminium chloride, induced cleavage of 2,2, 4,4 -tetramethoxy-benzophenone [1159]. 

A mixture of 38.6 g (0.1 mol) of 3,4,3, 4 -tetramethoxy-6-(a-acetopropyl)-benzophenone, 5.5 g (0.11 mol) of 100% hydrazine hydrate or 3.52 g (0.11 mol) of hydrazine, and 500 ml of absolute ethanol is boiled for 5 hours. After adding 100 ml of benzene, 400 ml of solvent mixture Is distilled off from the reaction mixture by slow boiling for 3 hours. After cooling for 8 hours, 19 g of 5H-2,3-benzodiazepine derivative are separated from the residue as small, white crystals. The melting point is 133°C to 1 36°C (after recrystallizing from absolute ethanol, 136°C). 

Block, Ledwith and Taylor (46) have reported the results of a detailed investigation into the efficiencies of benzof enone, 3,3, 4,4 -benzo-phenone tetracarboxylic dianhydride (BTDA) and 3,3, 4,4 -tetramethoxy-carbonyl benzophenone (TMCB) as photoinitiators for the polymerization of methyl methacrylate in tetrahydrofuran at C in vacuo. 

Hydroxy-5,6,7-trimethoxyxanthone, which was isolated for the first time from H. ericoides, was successfully synthesized by Gil et aL [59]. The synthesis was performed from the new benzophenone precursor 25 (Fig. 13). Compound 25 was prepared by Friedel-Crafts acylation of 1, 3,4-tetramethoxy-benzene with 2,5-dibenzyloxybenzoic acid and oxalyl chloride. When benzophenone 25 was heated with Me4NOH, 5-benzoyloxy-2-hydroxy-2, 3, 4, 5 -tetramethoxybenzophenone (25) underwent cychzation to 2-benzyloxy-5,6,7-trimethoxyxanthone (26) [60]. Hydrogenolysis of this compound with H2/Pd-C [61] finally afforded 2-hydroxy-5,6,7-trimethoxyxanthone (27) which is identical to natural xanthone [60]. 

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