5,6-Benzoquinoline

Benzoquinolines. Because certaia alkaloids are characterized by these more elaborate fused-riag systems, their syathesis has beea reviewed ia detail (138). Heatiag 4-methoxy-1-naphthylamine with epichlorohydrin produces a modest yield of... 

Acridine (2,3-benzoquinoline) [260-94-6] M 179.2, m 111° (sublimes), b 346°, pK 5.58 (pK of excited state 10.65). Crystd twice from benzene/cyclohexane, or from aqueous EtOH, then sublimed, removing and discarding the first 25% of the sublimate. The remainder was again crystd and sublimed, discarding the first 10-15% [Wolf and Anderson 7Am Chem Soc 77 1608 7955]. 

Benzoquinoline (phenanthridine) [229-87-8] M 179.2, m 108-109 , b 350 , pK 4.61. Chromatographed on activated alumina from benzene soln, with diethyl ether as eluent. Evapn of ether gave crystalline material which was freed from residual solvent under vacuum, then further purified by fractional crystn under N2, from its melt. Sublimes in vacuo. See also p. 324. 

Highly electron-deficient 1,3,6,8-tetranitronaphthalene 443 was reported to react in ethanol with A -methyl phenylacetamidines, e.g. 444, to give the corresponding benzoquinoline derivatives, e.g. 446 (77JOC435). Though the reaction mechanism of this double nitro group displacement is not known, formation of intermediate 445 and its following cyclization is probably the most reasonable explanation (Scheme 70). 

Hey and Osbond converted (18) to 5 6-benzoquinoline (19) with copper powder in dilute acid solution, reaction probably going through the dihydro compound (20) which was oxidized by nitrous acid in the... 

Cyclohexanones have been converted to 8-chloroquinolines through a series of reactions involving imination, a-alkylation with Af,N-disilyl protected oa-bromoamines, transimination, a-chlorination of the resulting bicyclic imines, dehydrochlorination and dehydrogenation <96T(52)3705>. A short, high yielding one-pot synthesis of acenaptho(l,2-b)benzoquinolines... 

The reaction network for 5,6-benzoquinoline [101] has been proposed in a more detailed level than that of acridine. In this network, conversely to acridine network, only one primary hydrogenation product, l,2,3,4-tetrahydro-5,6-benzoquinoline, was identified, and in contrast to the quinoline case however, no aniline derivatives were detected. 

Scheme 52 explains the [(Cp )Rh(MeCN)3]2+-assisted regioselective hydrogenation of pyridines, benzoquinolines, acridines as well as indoles and benzothiophene.258 The relative hydrogenation rates were attributed to both electronic and steric effects, the rate generally decreasing with increasing basicity and steric hindrance at the nitrogen atom. 

The photochemical isomerization of E-stilbenes has been applied in the preparation of phenanthrenes, as Z-stilbenes undergo electrocyclie ring closure (cf. chapter 3.1.3) to dihydrophenanthrenes which in turn are easily oxidized to phenanthrenes (3.1) 305). This sequence has also been employed in the synthesis of benzoquinolines 306) or of benzoquinolizines (3.2) 307). 

As a general trend, six-membered mononuclear N-heteroaromatics such as pyridine and derivatives are much less prone to undergo hydrogenation than bi-and trinuclear N-ring compounds (e.g., quinolines, benzoquinolines, acridines) due to their higher resonance stabilization energy. 

Prior work has been concentrated mostly on the isolation of distinct NSO compound classes from soluble organic matter. Often, selective extraction methods are applied as described for the isolation of, for example, phenols, [39,40] fatty acids [41] and basic nitrogen compounds such benzoquinolines... 

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