Quinolizinones

Quinolizinium salts, 2,4,6-trimethyl-condensation reactions, 2, 539 Quinolizinones reactions, 2, 544 synthesis, 2, 567 Quinolizinones, nitro-synthesis, 2, 568 Quinolizin-4-ones nitration, 2, 529 synthesis, 2, 565 2,2 -Quinolyl... 

Simple synthesis of ( )-17-epiyohimbol (73) has been reported by Mori et al. (214). yV-Benzyloctahydroindolo[2,3-a]quinolizinone (126), prepared according to the procedure of Novdk and Szdntay (97) was coverted to the corresponding pyrrolidine enamine, which was treated with methyl vinyl ketone to give N-benzylyohimbenone (379). Reduction of 379 with sodium in liquid ammonia... 

The C-hydroxylation of benzoquinolizinium ions is easier and, although the position of the attack on benzo[a]quinolizinium (2) salts is not known, it has been demonstrated (67JOC733) that hydroxylation of the acridizinium (benzo[6]quinolizinium, 3) ion must occur at position 6 (Scheme 8). It was not possible to obtain a pure sample of the pseudobase (17) or the 2-(2-formylbenzyl)pyridine (18) in equilibrium with it, but oxidation of the mixture with ferricyanide afforded a small amount of benzo[Z>]quinolizinone (19) (62CI(L)1292), while reaction with hydroxylamine afforded a good yield of 2-(2.-pyridyl-methyl)benzaldoxime (20) (67JOC733). 

These compounds offer interesting possibilities for further elaboration as they enter into addition reactions with, for example, the 1,2-quinone (60), yielding tricyclic compounds (61) (79TL237), and their bicyclic analogues (62) combine with phenyl isocyanate to give adducts (63), which eliminate carbon dioxide to afford pyrimidine betaines (64). Similarly, dialkyl acetylenedicarboxylates produce quinolizinones (65) (Scheme 19) (79CB1585). 

In the last sections, 3-nitro-2-pyridones 28 are synthesized by TCRT of nitropyrimidinone 3 with ketones 22 in the presence of ammonium acetate. The C2 - C3 - C4 unit of 28 is derived from the C4 - C5 - C6 unit of pyrim-idinone 3, which behaves as the synthetic equivalent of a-nitroformylacetic acid 29. The same partial structure is also found in l,3-dinitroquinolizin-4-one 35 [55], which is regarded as the dinitropyridone blocked with a benzene ring on the [/] face [56], and only a single kind of TCRT is expected to proceed. Nitropyridones 28 are actually prepared in moderate yields by TCRT upon treatment of quinolizinone 35 with ketones 22 in the presence of ammonium acetate as the nitrogen source (Table 7) [57]. 

Chebanov VA, Saraev VE, Desenko SM et al (2007) One-pot, multi-component route to pyrazolo-quinolizinones. Org Lett 9 1691-1694... 

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). 

New spectroscopic data on the 1 2 adduct (18) of pyridine and dimethyl acetylenedicarboxylate have been reported together with the products derived from it by oxidation and by thermolysis. Oxidation with potassium dichromate yields a mixture of the indolizine (19) and the quinolizinone (20).38... 

Apart from the reports mentioned above, there are sustainable monofunctional thioureas that successfully induce chirality. In 2007, Jacobsen and coworkers reported the enantioselective Pictet-Spengler cyclisation of hydroigrlactams. Utilising as little as 0.1 mol% of thiourea 10, indolizinone and quinolizinone products were afforded in high yields and high enan-tioselectivities (Scheme 19.14) via a counterion transition state. ... 

Benzo[a]quinolizinone rings can be obtained under mild conditions from aldehydes and cyclic amines containing active C-hydrogen as well as by facile one-step route... 

Miscellaneous. Keten dimer has been used in the synthesis of a variety of pyrones (171) through its reaction with 2-hydroxy-4-quinolizinone. 

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