Quinoline, 3,4-dihydro-, reaction with

N-Arylpiperazin-2-ones, N-arylpiperazin-2,5-diones and N-aryl-3,4-dihydro-quinolin-2(lff)-ones have been synthesized via a microwave-enhanced Goldberg reaction [105]. N-arylation reactions with 4-benzylpiperazin-2-one and 4-benzylpiperazin-2,5-dione performed in the microwave (reflux conditions) were tremendously accelerated in comparison with the same transformations performed under classical heating at reflux (Schemes 103 and 104). The phenylation of 3,4-dihydroquinolin-2(lH)-one under microwave irradiation was also faster but less pronounced. 

As already mentioned in CHEC-II(1996), 1,4-benzodioxins are often obtained from the corresponding dihydro compounds <1996CHEC-II(6)447>. Thus, elimination reactions of monoiodo and monobromo <2001HC0135> or dibromo benzodioxanes <2000EJM663> allow the formation of various 2-substituted-l,4-benzodioxins in good yields. 6-Methyl-l,4-benzoxathiin was prepared from the saturated derivatives by reaction with SOCI2, then quinoline <2003BML2083>. 

A series of l,2,4-triazino[5,6-c]quinolines have been prepared via a common route. Thus, 4-[fi-(ethoxymethylene)hydrazino]-3-nitroquinoline (244), prepared from 4-hydrazino-3-nitroquinoline (243) by reaction with triethyl orthoformate, was hydrogenated in ethanol over a palladium catalyst to give the dihydro compound (184) (96%). Dehydrogenation yielded the desired compound (185) (90%) (Scheme 19) <73GEP(0)2322394>. 

ET-initiated alkylation of azines in the presence of alkyl halides has been found to occur under electrochemical conditions according to Scheme 43. Either alkylated dihydroheterocycles or the rearomatized products are obtained. As an example, electroreduction of quinoline in the presence of 1-bromoadamantane gives alkylated quinolines (10 % in position 2, 5 % in position 7) and 2-methyl- and 2-methoxyquinoline give the 7-adamantyl derivative in 20 and 23 % yield, respectively. 1,10-Phenanthroline gives bis(adamantyl) derivatives, whereas isoquinoline and phenanthridine give the 6-adamantyl-5,6-dihydro and the 9-adamantyl-9,10-dihydro derivatives, respectively [132]. Reaction with terr-butyl chloride also gives alkylated dihydroheterocycles [133]. Arylation has also been performed, e.g. in the synthesis of pyrazolophenanthridines (62, Scheme 44) [134]. 

The addition product which is first formed, 2,3a-dihydro-lH-1,3,4-thiadiazolo[3,2-a]quinoline-2-thione (CXLVI), undergoes a redox-reaction with formation of the meso-ionic compound (CXLVII). 

Lithium in liquid ammonia conditions can produce l,4-dihydroquinoline" and 3,4-dihydroisoquinoline." Conversely, lithium aluminium hydride reduces generating l,2-dihydroquinoline" and 1,2-dihydroisoquinoline. These dihydro-heterocycles can be easily oxidised back to the fully aromatic systems, or disproportionate, especially in acid solution, to give a mixture of tetrahydro and re-aromatised compounds. Stable dihydro-derivatives (see also 9.13) can be obtained by trapping following reduction, as a urethane, by reaction with a chloroformate. Quaternary salts of quinoline and isoquinoline are particularly easily reduced, either catalyticaUy or with a borohydride in protic solution, giving... 

Narasimhan et al. (194) instituted a new approach to the synthesis of furoquinoline alkaloids by introducing a C2 side chain into a preformed quinoline nucleus. Lithiation of 2,4-dimethoxyquinoline, 2,4,6-tri-methoxyquinoline, and 2,4,8-trimethoxyquinoline with n-butyllithium in ether and subsequent reaction with ethylene oxide furnished hydroxyethyl derivatives 237, which with 20% hydrochloric acid were converted into dihydrodictamnine (239), dihydropteleine (240), and dihydro-y-fagarine... 

Disubstituted quinolines of type 21 were obtained from acetylenic ketones 2 as a result of a condensation reaction with 2-amino thiophenol 19 followed by sulfur extrusion (entry f). Acetylenic ketones have also been employed as dienophiles in Carbonyl-Alkyne-Exchange (CAE) reactions with dienes 22 (derived from 2,2-dialkyl-2,3-dihydro-4//-pyran-4-ones )(entry g) or 24 (entry h) to yield aromatic compounds 23 and 25 in a highly regioselective way. 

Banks, R.E. Haszeldine, R.N. Rohinson, J.M. Reactions of pyridine 1-oxides, 5-methylpyrimidine 1-oxide, and quinoline 1-oxide with perfluoropropene and perfluoro (2-methylpent-2-ene) synthesis of 2-(l,2,2,2-tetrafluoroethyl)pyridines or -pyrimidines and their A-oxides and of 2,2,3-trifluoro-2,3-dihydro-3-trifluoromethylfuro[3,2-h] pyridine. J. Chem. Soc., Perkin Trans. 1 1976, (11), 1226-1230. 

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