Indoles reaction with quinolines

Bromination of the diphenyl indole derivative 316 with bromine in DMF or trimethylammonium bromide afforded the 7-bromo derivative 317. Reaction with allyl bromide or its derivatives gave A-allyl derivatives 318 that upon cyclization with palladium acetate gave 7,9-dimethoxy-l,2-diphenylpyrrolo[3,2,l-// ]quinoline derivatives 319 (92T7601) (Scheme 57). 

Heterocyclic amines are compounds that contain one or more nitrogen atoms as part of a ring. Saturated heterocyclic amines usually have the same chemistry as their open-chain analogs, but unsaturated heterocycles such as pyrrole, imidazole, pyridine, and pyrimidine are aromatic. All four are unusually stable, and all undergo aromatic substitution on reaction with electrophiles. Pyrrole is nonbasic because its nitrogen lone-pair electrons are part of the aromatic it system. Fused-ring heterocycles such as quinoline, isoquinoline, indole, and purine are also commonly found in biological molecules. 

The indole nucleus can change during the synthesizing reaction into quinoline nucleus (Figure 32). Moreover L-tryptophan, the precursor, provides both /3-carboline and pyrroloindole nuclei. Iboga, Corynanthe and Aspidosperma nuclei also originate from L-tryptophan (Figure 32). Alkaloids with nuclei derived from this amino acid tend to be very active compounds with a relatively widespread provenance in nature (Table 10). 

Unsaturated 5(4//)-oxazolones derived from aromatic and heterocyclic aldehydes including phthalic anhydride/ antipyrine/ " chromone/ indoles/ pyridines/" ° quinolines/" diazines/" benzoxazoles/" and benzimidazoles " " have been prepared. Reaction with nitrogen nucleophiles and subsequent cycliza-tion leads to the expected 5(477)-imidazolones. 

Another example is the reaction of indoles with nitrosoarenes in the presence of acids. The redox potentials of the reactants cannot justify an outer-sphere ET process, thus the formation of the phenylaminoxyl detected for the reaction carried out in the ESR cavity, could be more likely justified by an inner-sphere ET mechanism95. In fact the reaction of quinoline N-oxide with primary alkyl Grignards for which an outer-sphere mechanism was earlier proposed, takes place through classical nucleophilic addition96. 

Intramolecular Diels-Alder reaction (with high periselectivity and good yields) of conjugated carbodiimides, catalyzed by Lewis acids, affords a simple procedure for the construction of pyrido[2,3-h]indole and indolo[2,3-ft]quinoline ring systems (equation 176)631. This procedure is superior to the often mixed reactions that occur in the absence of the Lewis acid632-635. It is interesting to note that Lewis acids also improve yields and selectivity in intermolecular reactions of this type636. 

The iminium ion electrophile can also be prepared separately, as a crystalline solid known as Eschen-moser s salt (Me2N =CH21 ) and, with this, the reaction is normally carried ont in a non-polar solvent. Examples that illnstrate the variation in iminium ion structure that can be tolerated include the reaction of indole with quinolines, catalysed by indium(lll) chloride, with benzylidene derivatives of arylamines, catalysed by lanthanide triflates, with ethyl glyoxylate imines " (no catalyst required) and with dihydro-1,4-oxazin-2-ones. °" ... 

The investigated supported complexes 22 and 23, outlined in Fig. 8, were used for hydrogenations of alkenes, nitriles and a,jS-unsaturated ketones. Furthermore, 23 was used in the reduction of different heterocycles like benzoth-iophene, quinoline, indole, dibenzothiophene and acridine. The supported chiral Rh complexes, depicted in Fig. 9, were used for hydrogenation reactions with prochiral olefins. 

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