By Alan R. Katritzky
This quantity within the sequence summarizes the various tools of the synthesis of heterocycles from azadienes with sections overlaying 1-azadienes, 2-azadienes, and 1,3-diazadienes. It covers the piperazine-2,5-diones and similar lactim ethers - complete overview of those hugely very important intermediates for the instruction of a wide selection of typical items. The e-book explains how 1,2,4-Triazolo [1,5-a] pyrimidines are of specific value in images with different major program in prescribed drugs and agrochemicals. It additionally studies tetramic acids, an importantgroup of common items exhibiting signifcant organic task, in addition to a few chemistry.
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Extra info for Advances in Heterocyclic Chemistry, Vol. 57
Studied the utility of 2-azadienes 136 as precursors of nitrogen-containing six-membered heterocycles; thus, 136 (R' = Me) underwent, in the presence of base, intramolecular 1,6 nucleophilic addition to the cyano group, giving rise to pyridines 163 in 85-90% yield (86HCA793). On the other hand, pyrazine 165 was isolated in 71% yield on exposure of the appropriate azadiene 136 to HBr; bromoimine 164 seems to act as intermediate in the process (90HCA1210). 2-Azadienes having cyano and amino substituents at positions 1,4 are expected to cyclize to the pyrimidine ring.
We also discovered the ability of 2-azadienes of this sort to cycloadd to unactivated carbon-carbon double and triple bonds in an intramolecular fashion (89CC267) (Scheme 50); such a process appears to be one of the first examples of intramolecular [4 + 21 cycloadditions of simple 2azadienes. Azadiene 216 was made from 0-ally1 salicylaldehyde 215 (R = allyl) and heated at 120°C in toluene to furnish the trans-fused tricyclic adduct 217 in excellent yield; further dehydrogenation of 217 with DDQ afforded 5H-[l]-benzopyran[4,3-b]pyridine 218.
Have succeeded in the 1,Zannulation of pyridine itself to the vinyl carbodiimide unit of 248 to produce pyrido[ 1,2f]pyrimido[4,5-6]pyrimidines 249 (91TL4473) (Scheme 56). Molina et af. have been able to cyclize systems 250, in which the dienophilic partner can be substituted with either electron-donating or -acceptor groups, to give a-carbolines 252 in 31-55% yield; the participation of one aromatic carbon-carbon double bond in the cycloaddition process was also shown to occur since diary1 carbodiimides 253 furnished, under the same reaction conditions, quinindolines 255 in 28-54% yield.