Nitrate reduction system scheme

The l-benzazepin-2-one system continues to be a target for synthesis because of the pharmacological activities of compounds with this skeletal unit. In this context, a ring-enlargement route to 337 on treatment of 336 with silver nitrate has been reported (Scheme 45). This reaction presumably proceeds via an aziridinium ion intermediate. The structure of the product was confirmed by reduction of 337 to 338. The possible isomeric product 339 was made separately and shown to be different <2002SL1350>. 

The only reliable method of introducing a fluoro substituent into an aromatic system is through the diazotisation and subsequent fluorination (Scheme 12) of the appropriate aromatic amine (40), which is in turn generated from the reduction of the nitroarene (39) generated from the nitration of the basic aryl unit (1). However, there are maity simple fluoro-substituted materials that are coimnercially available and so generally the synthesis of most fluoro-substituted target molecules can begin with the fluoro substituents already present. 

Photoredox systems coupled to biocatalysts Interesting variation of photoredox systems can be obtained if one replaces the homogeneously or heterogeneously redox catalysts by redox enzymes. With appropriate enzymes it is possible to use the redox equivalents to achieve other useful chemical reactions such as reduction of CO2 to methane, nitrate to ammonia etc. Willner et al. [66,67] in particular have exploited this approach and have obtained interesting results. Scheme below illustrates the sequence of reactions that take place in a typical photochemical system of this kind. 

This approach for the synthesis of macrocycles with quinoxaline moieties involves the development of methods for the introduction of amino groups to the adjacent carbon atoms of the planned unit of the macrocycle system. Two methods (Crossley et al. 1996a) have been developed for the synthesis of diaminoporphyrin 6. The first involves the reduction of the nitro group to the amino group of the compound 53 with sodium borohydride in the presence of the Pd/C and subsequent regioselective nitration (Scheme 5.13). The second one is the nucleophilic substitution of hydrogen by NaNHCHO and subsequent hydrolysis. Both methods lead to... 

Several streptonigrin quinoline-quinone analogs have also been synthesized by Rao (16) (Scheme 6) using a modified Friedlander synthesis for construction of the quinoline system. The compound prepared which structurally is most like the natural product is the pyridylquinoline-quinone (59). Chalcone (55), prepared from 3,5-dimethoxybenzaldehyde and 2-acetylpyridine, was nitrated to give (56). Reductive cyclization of (56) with sodium dithionite led to quinoline (57) which upon treatment with nitric acid/sulfuric acid yielded nitroquinone (58) in 50% yield along with 40% of a product of straightforward mononitration. Reduction of the nitro group of (58) and 0-methylation with diazomethane afforded (59). 

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