Quinolizinone ring

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). 

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... 

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]. 

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