4-Quinolones, ring synthesis

In the synthesis of these compounds, the 2-(l-chloro-2-fluoroethyl)thio compound 200 has been debenzylated and intramolecular cyclization was carried out to afford the 1,3-thiazetidine ring in compound 201 (Scheme 65). The alternative /3-elimination reaction is inhibited because the lone pair of electrons on the sulfur atom of the anion is delocalized on the quinolone ring and so cannot attack the cr-carbonatom of the chlorosulfenyl group <1999CPB1765>. 

The aza-annulation methods developed for conversion of 88 to 94 were extended to the synthesis of the antileukemic and antitumor natural product ( )-camptothecin (125, Scheme 11 ).47 Aza-annulation of 109 with 121 in the presence of NaBH4 resulted in heterocycle formation to give 122 without subsequent elimination of the malonate species. A dye sensitized photo-oxidation promoted the rearrangement of the indolo[a]quinolizinone ring to the indolizino[l,2-h]quinolone ring 123. Compound 123 was converted to 124, which constituted a formal total synthesis of camptothecin (125). 

A -Acetylisatin, after ring-opening by base to the a-keto carboxylate 71, undergoes an intramolecular aldol condensation producing 2-quinolone-4-carboxylic acid 72. In the same way, o-A-acylaminoaryl ketones 73 can be made to cyclize to give either 2- or 4-quinolones Camps synthesis) ... 

The Spiro-compound (119), formed by the photoreaction of ethyl diazoacetate and diketen, is a versatile synthon for ring synthesis. Thus its reaction with aniline, followed by acid-promoted cyclization of the resulting anilide (120), gives the quinolone (121) (Scheme 48). ... 

Scheme 8.95 Synthesis of 2-quinolones ring from 3,3-diarylacrylamides.

Total Synthesis of Meloscine Meloscine 189, a member of the Melodinus alkaloids group, is noted for containing a six-membered quinolone ring within a mono-terpenoid Aspidosperma carbon skeleton. 

Pemberton N, Chorell E, Almqvist F (2006) Microwave-Assisted Synthesis and Functionalization of 2-Pyridones, 2-Quinolones and Other Ring-Fused 2-Pyridones. T. 1-30... 

Table 2 A comparison between conventional heating and microwave-assisted synthesis in an intramolecular Heck coupling to heterocyclic derivatives of 2-quinolones 20 and 21. Note the high selectivity in (b), where two possibilities exist to fuse a six-membered ring...

A review of Claisen rearrangements in aqueous solution has appeared. The synthesis of natural products utilizing tandem Diels-Alder additions with sigmatropic rearrangement processes has been reviewed, and a brief review of the regioselective synthesis of coumarins, quinolones and thiocoumarins with 3,4-fused pyran or furan ring systems by the Claisen rearrangement has been presented. ... 

In another synthesis of quinolines involving imine intermediates, o-oxazoline-substi-tuted anilines (6) react with ketones in dry butanol reflux to give 4-amino-substituted quinolines [e.g. (7)], or 4-quinolones, using tosic acid as catalyst.18 A mechanism involving ketoimine formation with subsequent tautomerization to give an enamine which attacks the oxazoline ring is discussed. 

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