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Read e-book online Advances in Heterocyclic Chemistry, Vol. 57 PDF

By Alan R. Katritzky

ISBN-10: 0120207575

ISBN-13: 9780120207572

This quantity within the sequence summarizes the numerous tools of the synthesis of heterocycles from azadienes with sections protecting 1-azadienes, 2-azadienes, and 1,3-diazadienes. It covers the piperazine-2,5-diones and comparable lactim ethers - accomplished assessment of those hugely vital intermediates for the education of a wide selection of typical items. The ebook explains how 1,2,4-Triazolo [1,5-a] pyrimidines are of specific significance in images with different major software in prescribed drugs and agrochemicals. It additionally studies tetramic acids, an importantgroup of traditional items exhibiting signifcant organic job, in addition to a few chemistry.

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They reported that azadiene 94 (n = 1) cyclized to 95, whereas compound 94 (n = 0) did not undergo intramolecular cycload- Sec. Bl 21 SYNTHESIS OF HETEROCYCLES FROM AZADIENES M P 5 mmHg q A,& 0 91 (n = 12) 92 mmHg 93 (46-80%) SCHEME 23 dition on heating to 200°C. On the other hand, the unactivated alkyne function also cycloadded with the I-azadiene system since pyridines 97 were formed in moderate yields when solution of 58 was heated in 1,2dichlorobenzene; compounds 97 should arise from aromatization of intermediate Diels-Alder cycloadduct 96.

The preparation of 2-azadienes 212 with two appended methoxycarbonyl groups was achieved, in a multigram scale and in nearly quantitative yield, by the insertion reaction of N - trimethylsilyl imines 210 into the carbon-carbon triple bond of dimethyl acetylenedicarboxylate to give 211 followed by protodesilylation with CsF/MeOH. Azadienes 212 underwent at room temperature inverse-electron demand [4 + 21 cycloaddition with cyclic enamines to give exclusively em-cycloadducts 213 in 82-95% yield. Acid hydrolysis of them resulted in their aromatization to yield 2-pyrindine (n = 13 and isoquinoline (n = 2) derivatives 214.

Among other leading workers in this field were Saegusa (81JA5250; 83TL2881; 86SC1073), Kametani (84TL4541; 85CC1159, 85H1097), and Dolle (88TL6349),who employed o-quinone methide imines, 2-trialkyloxysilyl-1-azabutadienes, and 1-dimethylamino-1-azabutadienes,respectively, as the reactive heterodienes in the intramolecular cycloaddition. Despite the fact that 4-amino-1-azadienes 2 are not capable of undergoing Diels-Alder cycloaddition processes, they become suitable substrates for preparing six-membered nitrogen heterocycles by [4 + 21 heterocyclizations (Scheme 26).

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Advances in Heterocyclic Chemistry, Vol. 57 by Alan R. Katritzky

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