Photochemical transformations of small ring heterocyclic compounds. XXXVII. Thermal and photochemical reactions in the 1,5-diazabicyclo[5.1.0]octa-3,5-diene system

Abstract

octa-3,5-diene (5) was prepared by treating ira«5-2-benzoyl-3phenylaziridine with cinnamaldehyde in an ethanolic solution saturated with ammonia. Treatment of 5 with sodium methoxide gave a high yield of fra/ij-2-styryl-4,6-diphenyl-l,2-dihydropyrimidine (6). Ultraviolet irradiation of 5 has been found to afford four products whose structures are identified as 1,4,8-triphenyl-2,5-diazaocta-1,3,5,7-tetraene (13), ?ro/zs-2-styryl-3,6-diphenyldihydropyrazine ( 14), rra«5-2-styryl-3,6-diphenylpyrazine (15), and 3,6-diphenyl-5,6-dihydrobenzo[/]quinoxaline ( 16). The formation of 16 from 5 was resolved into a sequence of four discrete reactions involving ring opening to 13, thermal electrocyclization, photooxidation, and photocyclization.

Transient Azomethine-ylides from a Stable Amino-carbene and an Aldiminium Salt

“…The structure of 3a , unambiguously determined by multinuclear NMR spectroscopy and by a single-crystal X-ray diffraction study, is somewhat surprising since the aromaticity of the aryl group is lost. The formation of 3a most likely results from the electrocyclization of the related azomethine ylide 4a ).…”

1,5-Dipolar cyclizations

“…Methyl substitution on the (3-carbon retards 1,5-dipolar cyclization; nitrogen elimination and subsequent cyclopropene formation become the main mode of decomposition. For example, 185 when heated with sodium methoxide affords 1,3,3-trimethylcyclopropene (187) in 72% yield via vinylcarbene 186.74…”

Fused aziridines as sources of azomethine ylides

“…Reaction of the azomethine ylides 17 and 20 with benzaldehydes takes place regioselectively, leading to derivatives of oxazolo[3,2-a]quinoxaline 18 and 21 [12,13] By the thermolysis of aziridines fused with seven-membered rings at the C-N bond in the presence of various dipolarophiles it is possible to synthesize (5,7)-bicyclic heterocycles. Refluxing of the azirinobenzodiazepine 22 in xylene in the presence of fumaronitrile leads to the stereoselective formation of the 1,5-diazabicyclo [5.3.0]deca-3,5-diene derivative 24 [14]. In the absence of the dipolarophile the 1,4-diazabicyclo[4.1.1]octa-2,4-diene derivative 25 is obtained as the main product, and it is probably formed as a result of 1,7-electrocyclization of the ylide 23.…”