By Alan R. Katritzky
This quantity within the sequence summarizes the numerous tools of the synthesis of heterocycles from azadienes with sections masking 1-azadienes, 2-azadienes, and 1,3-diazadienes. It covers the piperazine-2,5-diones and comparable lactim ethers - accomplished overview of those hugely vital intermediates for the practise of a large choice of typical items. The booklet explains how 1,2,4-Triazolo [1,5-a] pyrimidines are of specific significance in images with different major program in prescribed drugs and agrochemicals. It additionally reports tetramic acids, an importantgroup of ordinary items exhibiting signifcant organic job, in addition to a few chemistry.
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Additional resources for Advances in Heterocyclic Chemistry, Vol. 57
32 JOSE BARLUENGA AND MIGUEL TOMAS [Sec. - CyNC 0 M ~ Me CO2H * NaH 86 90 H 145 146 Meoy15 M e MeOH 85 % w +--) Me M e 0 Med 147 148 Me M$e Me0 149 SCHEME36 Sec. B] 33 SYNTHESIS OF HETEROCYCLES FROM AZADIENES M e S q AFNH-NHZ * Benzene 125°C %**o + ” ” i 7fN-Ar Y 0 OH 150 r \ ih3-NF 152 15 1 SCHEME 37 B. SIX-MEMBERED RINGS 1. From [6 + 01 Fragments Electrocyclic ring closure reactions of vinyl or aryl 2-azadienes (azatrienes) involving six electrons have been reported to occur at moderate temperatures and, in this respect, several pyridine syntheses have been described.
O] I H 255 (Y = CH=CH) 256 (Y = 0, S; RZ = H) SCHEME 57 of iminophosphorane 260 and diphenylketene and cycloadded to a second molecule of diphenylketene to furnish 1,3-oxazine derivative 262 in 60% yield [89JCS(P1)2140]; in addition, the [4 + 21 cycloaddition reaction of 261 with aryl isocyanates and diary1 thioketones has just been reported (92LA 15). Isolated examples of intramolecular [4 + 21 cycloaddition reac- 52 JOSE BARLUENGA AND MIGUEL TOMAS [Sec. 8 I R2 257 Ph ph2C=C=o * 9 Ph Ph2C=C=O '**yPh 261 Ph * # Ph 'k: Ph 262 SCHEME 58 tions involving the 2-azadiene unit of a ketenimine have been published (91TL5379; 92JOC929).
Similarly, reaction of 182 with triethyl orthoesters and aromatic aldehydes afforded pyrazines 187 in 43-91% yield; diazatrienes 185 and 186 generated from orthoesters and aldehydes, respectively, underwent electrocyclic ring closure and aromatization by elimination of ethanol or dehydrogenation. When working with substituted 2-azadienes 139, we were aware of their behavior as divinyl amines; in fact, their reaction with trimethylsilyltriflate 38 JOSE BARLUENGA AND MIGUEL TOMAS [Sec. B R2 90-140°C 73-78 % 20°C X X 179 180 C02Et.