2- diphenylamine cyclisation

In the second step the reaction is less efficient because of quenching of the excited state of the diphenylamine component by the adjacent carbazole. Other cyclisations such as the conversion of (41) into (42) by irradiation in acetic acid have also been reported. As mentioned earlier cw-azobenzene derivatives cyclise under conditions where the nitrogens are protonated or complexed. A series of heavily substituted azobenzenes has been shown to undergo photochemical cyclodehydrogenation on irradiation in methylene dichloride solution with added SnCU- The reaction has been shown to be an efficient path to the heavily methylated cinnolines in good yield. 

Quinacrine may be easily prepared starting form 2,4-dichlorobenzoic acid (90). Ullmann reaction of 90 with p-anisidine (91) gives the desired diphenylamine 92, which is cyclised to form the 9-chloroacridine derivative (93). Condensation of the latter with l-diethylamino-4-aminopentane affords quinacrine (22) [71]. A similar sequence of reaction starting from 90 and 5-amino-2-methoxypyridine (94) gives azocrine (28) [72] (Scheme 3). 

The photochemically induced cyclisation of diphenylamines to carbazoles is well established in the chemical literature. Details of the first example of such a cyclisation in W,W-diarylsulphon-amides have been published, and a similar conversion of the N-phenylenamine (35) into the indoline (36) has been used in a new synthesis of oxindoles. Analogous cyclisations accompanied by the elimination of HX have also been reported the pyridinium bromide (37), for example, is converted in this way into the pyridoisoindolium bromide (38). °... 

Jackson et al. have reported yet another refinement of the Cranwell-Saxton synthesis of ellipticine, and have also investigated a new route, which has so far resulted in the preparation of the intermediates, (176a) and (176b). In principle, these diphenylamine derivatives should be convertible into AT-acetyl-ellipticines by thermal cyclisation and dehydrogenation, or into ellipticine by photo-cyclisation of the free amines. Although a considerable amount of (176a) was prepared, its conversion into 9-methoxyellipticine has not yet been reported. 

Condensation of l-bromo-2-methoxy-4-methyl benzene (64) with 5,6-dimethoxyaniline acetate (65) in pyridine in the presence of Cu and K2CO3 and subsequent hydrolysis with 20% KOH furnished the di-phenylamine derivative (66) which on treatment with palladium acetate in DMF afforded murrayastine (13). Condensation of l-bromo-3-methoxy-4-methylbenzene (67) with the dimethyl acetal of 6-formyl-5-methoxyaniline acetate (68) furnished the diphenylamine derivative (69) which on hydrolysis and on subsequent cyclisation furnished murray-aline (14). 

For synthesis of pyrayaquinone A and pyrayaquinone B 42) 7-Amino-2,2-dimethyl-chromene (122) prepared from m-hydroxyacet-amide (123) gave on condensation with 2-methylbe(nzoquinone (124) diphenylamine (125) which on cyclisation with pall ium acetate afforded pyrayaquinone A (25). Similarly 5-amino-2,2-dimethylchromene (126) on condensation with 2-methylbenzoquinone (124) afforded the diphenylamine derivative (127) which on cyclisation by the above method furnished pyrayaquinone B (26). 

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