Highly fluorescent and stable 6,7-dimethoxy-2-oxoquinoline-4-carbonitriles (11) were synthesized starting from appropriate 4-hydroxyquinolones 3 via reactive 4-chloroquinolones 8 by using toluenesulfinates as catalysts. In contrast to the well-described 4-trifluoromethyl-substituted analogues 18, N-substituted derivatives 11 fluoresce in water, polar, and apolar solvents in a narrow 430-440-nm window with almost constant quantum yield of 0.5. Equal excitation is possible in the broad double maximum between 385 and 410 nm yield-

4-Hydroxy-3-phenylsulfanyl-2-quinolones 2 and 4-hydroxy-3-sulfonyl-2-quinolones 7, which are readily accessible from 4-hydroxy-2-quinolones 1 and diphenyldisulfide or thiophenol, can be converted to 4-azido-3-phenylsulfanyl-2-quinolones 10 or 4-azido-3-phenylsulfonyl-2-quinolones 12 via 4-chloro-3-phenylsulfanyl-2-quinolones 5 or 4-chloro-3-phenylsulfonyl-2-quinolones 9, respectively. Thermolysis of the azides 1 0 and 1 2 results in a cyclization reaction to give quinolino [3,4-b] Organic azides with reactive ortho-groups such as aryl-, heteroaryl-or acyl groups are known to decompose on thermolysis or photolysis followed by a cyclization to heterocycles, either via a nitrene or an electrocyclic mechanism [2]. Mainly, this cyclization type leads to five-membered heterocycles. Two typical examples are the attack of the azide nitrogen either to the 2-position of a phenyl ring in ortho-position to the azide forming indoles [3], or by attack of the azide nitrogen to e.g. the oxygen atom of a carbonyl group in ortho-position to the azide forming isoxazoles [4]. Only in a few cases, the formation of six-membered heterocycles is reported [2], e.g. with a benzyl substituent in ortho-position of the azido group; in this way we obtained from 4-azido-3-benzyl-2-quinolones in good yields dibenzo [b,h][1,6]naphthyridin-6-ones [5]. S i m i l a r l y, the phenylsulfanyl group, Ph-S, or their oxidized variants, the phenylsulfoxide group, Ph-SO, and the phenylsulfonyl group, Ph-SO 2 , seemed to be good candidates for such a thermal azide cyclization.Recently a direct sulfenylation of 4-hydroxy-2-quinolones by the action of diphenyl disulfide has been developed in our group [6,7]. This reaction sequence was used, in this contribution, in order to obtain 4-azido-2-quinolones with phenylsulfanyl groups in 3-position as suitable starting materials for the planned thermal cyclization of azides to six-membered heterocycles. The reaction of 4-hydroxy-2-quinolones 1 with diphenyl disulfide was carried out as described in references [6,7] under basic conditions. During the reaction the thiophenolate anion was formed, which was oxidized by oxygen back to diphenyl disulfide. In contrast to the earlier described method [7], we obtained better results when the air for oxidation was not bubbled through the reaction mixture, but compressed air was blown onto the mixture with a tube ending above the surface of the reaction mixture. This was because the inlet pipe often was clogged when air was bubbled through the mixture. In this way the amount of employed diphenyl disulfide could be reduced to a halfmolar amount and the 3-phenylsulfanyl-2-quinolones 2a-c were obtained in good to excellent yields. There is also the possibility to obtain the thioethers 2 from thiophenol and 3-chloro-4-hydroxyquinolones 4 in pyridine as basic solvent in excellent yields, however this method needs two more steps.

Depending on the ester substituent, diethyl 2‐(3‐nitro‐2‐oxo‐4‐quinolinyl)malonates 2 give upon thermolysis ethyl 2‐(3‐nitro‐2‐oxo‐4‐quinolinyl)acetates 4, whereas dimethyl 2‐(3‐nitro‐2‐oxo‐4‐quinolinyl)‐malonates 3 cyclize to give 1‐methoxycarbonylisoxazolo[3,4‐c]quinolin‐4(5H)‐ones 5. The necessary reaction conditions can be obtained easily with the help of differential scanning calorimetry.

4‐Chloro‐ or 4‐tosyloxyquinolines 1 and 10 react with CH‐acidic compounds such as malonates 2a,b, ethyl cyanoacetate (2c), malononitrile (2d), ethyl acetoacetate (2e), acetylacetone (2f) or dimedone (2g) under mild conditions and good yields to quinolin‐4‐yl substituted derivatives 3‐8 and 11. With 3‐phenylsulfonylquinolones 1i‐k a redox reaction to 2‐hydroxy‐2‐quinolin‐4‐yl‐malonates 9 was observed. Amination of 3‐nitroquinolinyl malonate 3f leads to malonester‐amides 13 and 14.

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