Photoextrusion of Molecular Nitrogen from Annulated 5-Alkylidene-4,5-dihydro-1H-tetrazoles: Annulated Iminoaziridines and the First Triplet Diazatrimethylenemethane

Abstract

Deprotonation of the annulated tetrazolium salts 4, 6, 8, 10, and 12 with sodium or potassium hydride yields the alkylidenedihydrotetrazoles 5, 7, 9, 11, and 13, respectively. While 5a and b are unstable, even in solution at low temperatures, 7, 9, 11, and 13 form yellow oils that are distilled under high vacuum. − Irradiation of solutions of 7, 9, and 11 in [D8]toluene at −60°C yields, besides molecular nitrogen, annulated iminoaziridines that have an exocyclic CN double bond, i.e. 14, 16, and 18, respectively. In addition, an equal amount of the isomer 19 with the endocyclic CN double bond is formed from 11. On thermolysis, 14, 16, and 18 undergo [2 + 1] cycloreversion into methyl isocyanide and the cyclic imines 15, 17, and 20, respectively. By contrast, 19 rearranges thermally to yield 18. While the doubly bridged alkylidenedihydrotetrazole 13a affords only unidentified decomposition products on photolysis, its methyl homologue 13b is converted into the hexahydronaphthyridine 22 which is also formed on thermolysis. − Irradiation of 13b in a 2‐methyltetrahydrofuran or butyronitrile matrix at 77 K yields a triplet diradical showing a four‐line EPR spectrum centred at 3362 G and a half‐field transition (at 1669 G) with a hyperfine structure. The zero‐field splitting parameters |D‐hc| = 0.031 cm−1 and |E‐hc| = 0.0014 cm−1 are obtained by simulation of the EPR spectrum. The signal‐carrier is assigned the diazatrimethylenemethane structure 23 on the basis of the close similarity between its EPR spectrum and those of trimethylenemethane (28) and tris(N‐methylimino)methane (29). − Structural features are discussed that are responsible for the observed differences between the photochemical pathways.

Photochemical Transformations of Tetrazole Derivatives: Applications in Organic Synthesis

“…In 1998, Quast and Fuss described the synthesis of different annulated iminoaziridines by photolysis of 5-alkylidene-4,5-dihydro-1 H -tetrazoles in solution [53]. During this study, diluted degassed solutions of alkylidenedihydrotetrazoles 25 , 27 and 29 were irradiated (λ ≥ 305 or 320 nm; high pressure mercury lamp) in [D 8 ]toluene, affording annulated-iminoaziridines with an exocyclic CN double bond, i.e.…”

“…Several tetrazole derivatives have also been studied regarding their photochemical fragmentation reactions, matrix-isolated or in solution [32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54]. Results show that the photodecomposition of tetrazoles always involves cleavage of the tetrazolyl ring, leading to a variety of photoproducts.…”

Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on photoproduct selectivity

“…Azides, isocyanates or aziridines are generally obtained, but the presence of labile hydrogen atoms, either directly linked to the tetrazole ring or in substituent groups, may open additional photocleavage pathways or allow for secondary photochemical reactions to take place concomitantly with the main primary photoprocesses. [4][5][6][7][8][20][21][22][23][24][25][26] The photochemistry of tetrazoles is also influenced by the chemical nature and conformational flexibility of substituents linked to the heterocycle, which may favor or exclude certain reaction channels, [9][10][11][12][13][14] determining the nature and relative amount of the final photoproducts.…”

“…28 Analysis of the literature reveals that, through a careful selection of the solvent and other reaction conditions, the photofragmentation of some derivatives of tetrazole may be tuned to grant selectivity and high yield, affording stable and synthetically useful photoproducts that may be isolated and stored, or trapped in the reaction media. A diversity of photoproducts such as 9H-pyrimido(4,5-b)indoles, 24 diaziridinones, 16,25 iminoaziridines, 26,27 carbodiimides, 22,25 oxazines, 14 benzimidazolones 22 and pyrimidinones 10,11 may be obtained from photolysis of tetrazole derivatives in solution. Of the 7 classes mentioned, 3 (diaziridinones, benzimidazolones and pyrimidinones) result from photolysis of 1,4-disubstituted-1,4-dihydro-5H-tetrazol-5-ones (tetrazolones), illustrating their versatility as starting materials for the preparation of other scaffolds and the relevance of a deep investigation of the photochemistry of this particular class.…”

Cyclization Cascade of Allenyl Azides: Synergy Between Theory and Experiment

“…By analogy with TMM chemistry, the ATMM variant might provide ready access to polycyclic nitrogen-containing cyclopentanoid alkaloid-like frameworks. The development of ATMM chemistry has lagged far behind its all-carbon relative, but early reports suggested its intermediacy in “triaza” decomposition chemistry [4–6], and seminal investigations by Quast on triazoline decomposition chemistry in the 1970’s--1980’s provided the first systematic and robust evidence for the existence of this elusive species [7–12]. Futhermore, this earlier work also led to the expectation that (1) inter molecular allene/azide cycloaddition would not be a viable route to precursor triazolines due to incompatible regiochemistry, and (2) facile ATMM closure to the iminocyclopropane might render diyl capture problematic (Fig.…”