Photochemistry of N-heterocycles. Part 1. Synthesis and photochemistry of some 2(4),5-dihydro-1,2,4-triazines. X-Ray molecular structure of 1-(4-methyl-3,5,6-triphenyl-1,4,5,6-tetrahydro-1,2,4-triazin-6-yl)ethanol

Nagy, József; Nyitrai, J.; Kolonits, Pál; Lempert, K.; Gergely, Anna; Pa̋rkányi, László; Kàlmán, Alajos

doi:10.1039/p19880003267

Cited by 17 publications

(14 citation statements)

References 5 publications

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“…H-atom transfer from the 2-hydroxypropyl radical logically formed from 2-propanol. That such solvent derived radicals are indeed formed is evident from the alkylations of heterocycles related to those used in this study, namely hydroxyethylation of 4-methyl-3,5,6-triphenyl-4,5-dihydro-1,2,4-triazinium chloride at C(6) [2] or the introduction of an isopropyl group at C(4) of 3,6-diphenylpyridazine (18). The formation of fully unsaturated products (3a,b, 12) under reducing (!)…”

Section: Discussionmentioning

confidence: 90%

“…Although the first synthesis of 1,4-dihydropyrimidine 2a was reported many years Photochemistry of N-Heterocycles. 7 1 ) 2 ) ago [4], the first reliable one with well reproducible results was published only in 1985 [5]. The dehydration of 1b to 2b was not described in the latter article.…”

Section: 4-dihydropyrimidinium Chloridesmentioning

confidence: 87%

“…These reactions have been rationalized in terms of initial hydrogen atom transfer from the solvent to the excited protonated heterocycle followed by radical combination [1a,b].More recently, the photochemically induced ring contractions and reductions of 1,2,4-triazine derivatives, especially of 2,5-dihydro-3,5,6-triphenyl-1,2,4-triazinium chlorides [2], have been rationalized as being initiated by photoinduced electron transfer (PET) reactions from the solvent alcohol (as donor) to the excited cyclic iminium ions (as acceptors) similar to the well-known PET reactions in the 4,5-dihydro-3H-pyrrolium series [3]. It was therefore expected that suitable dihydropyrimidinium, dihydro-1,3,5-triazinium, and dihydro-1,2,4, 5-tetrazinium salts also show analogous PET initiated photoreductive ring contractions.…”

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Light Induced Reductive Ring Contractions of Sixmembered Cyclic Iminium Ions

et al. 2000

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Upon electronic excitation in acidified methanol, pyridine undergoes methylation [1a].A similar reaction has been observed for quinoline and isoquinoline in ethanol containing hydrogen chloride [1b]. These reactions have been rationalized in terms of initial hydrogen atom transfer from the solvent to the excited protonated heterocycle followed by radical combination [1a,b].More recently, the photochemically induced ring contractions and reductions of 1,2,4-triazine derivatives, especially of 2,5-dihydro-3,5,6-triphenyl-1,2,4-triazinium chlorides [2], have been rationalized as being initiated by photoinduced electron transfer (PET) reactions from the solvent alcohol (as donor) to the excited cyclic iminium ions (as acceptors) similar to the well-known PET reactions in the 4,5-dihydro-3H-pyrrolium series [3]. It was therefore expected that suitable dihydropyrimidinium, dihydro-1,3,5-triazinium, and dihydro-1,2,4, 5-tetrazinium salts also show analogous PET initiated photoreductive ring contractions. From the results reported here it will become evident that this expectation is met. Results and Discussion 1,4-Dihydropyrimidinium chloridesThe preparation of the starting materials 2 will be commented briefly (Scheme 1). Although the first synthesis of 1,4-dihydropyrimidine 2a was reported many years The dehydration of 1b to 2b was not described in the latter article. Compounds 2a and 2b are in equilibrium in solution with their 1,6-dihydro tautomers [6] and are very sensitive towards dehydrogenation to the fully unsaturated analogues 3a,b [7] (Scheme 1). We found that the method of Weis [5] was not suitable for the synthesis of 2b, but a slightly modified version proved to be successful. TLC monitoring showed that in the reaction of benzamidinium chloride with 1,3-diphenyl-2-propen-1-one using sodium methoxide in acetone solution, the formation of the aromatic pyrimidine 3b could be avoided if the amount of the base did not exceed 70% of the equimolar amount.Abstract. Photochemically induced reductive ring contractions, previously observed for 2,5-dihydro-1,2,4-triazines, have also been verified for 1,4-dihydropyrimidines 2a,b, the dihydro-1,2,4,5-tetrazine 9, and dihydro-1,3,5-triazines 11a,b giving rise to fivemembered fully unsaturated heterocycles (pyrroles 4a,b, imidazoles 13a,b, and triazole 10, respectively). The 1,4-dihydropyrazines 15a -j tend to decompose in acidified 2-propanol in the dark, but on irradiation they also undergo reductive ring contraction furnishing solely the 1,2,5-triarylpyrroles 16a-d rather than the (a priori also possible) isomeric 1,3,4-triarylpyrroles 17a -d. In contrast, the 3,6-diphenylpyrid-azine 18 gives the 4-isopropyl-analogue 19 in low yield upon irradiation in hydrogen chloride saturated 2-propanol.

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Section: Discussionmentioning

confidence: 90%

Section: 4-dihydropyrimidinium Chloridesmentioning

confidence: 87%

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Light Induced Reductive Ring Contractions of Sixmembered Cyclic Iminium Ions

et al. 2000

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“…3,5,6‐Triphenyl‐1,2,4‐triazine ( 5a ): yellow crystals (68.8 mg, 89 %); mp 144.0–145.0 °C (hexane/ethyl acetate); R f 0.50 (hexane/ethyl acetate, 4:1); 1 H NMR (400 MHz, CDCl 3 ) δ 8.69–8.67 (m, 2H, Ar), 7.69 (d, J = 7.2 Hz, 2H, Ar), 7.63 (d, J = 6.6 Hz, 2H, Ar), 7.58–7.56 (m, 3H, Ar), 7.48–7.36 (m, 6H, Ar); 13 C NMR (100 MHz, CDCl 3 ) δ 161.4, 155.7, 155.6, 136.1, 135.7, 135.0, 131.7, 130.8, 130.0, 129.7, 129.6, 129.0, 128.7 (×2), 128.5; HRMS (ESI): m/z [M + H] + calcd. for C 21 H 16 N 3 + : 310.1339, found 310.1339.…”

Section: Methodsmentioning

confidence: 99%

Gold‐Catalyzed Oxidation of Internal Alkynes into Benzils and its Application for One‐Pot Synthesis of Five‐, Six‐, and Seven‐Membered Azaheterocycles

et al. 2019

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Internal alkynes have been shown to undergo oxidation to substituted benzils (1,2‐diarylethane‐1,2‐diones) by α‐picoline N‐oxide in the presence of Ph3PAuNТf2 (5 mol‐%). In addition to the unsubstituted benzil, the method allows preparing, under markedly mild conditions (50 °C in chlorobenzene), various non‐symmetrical products, including heteroaromatic versions thereof which are much more difficult to obtain otherwise. This gold(I)‐catalyzed transformation was integrated into one‐pot reaction sequence delivering a range of 5‐ to 7‐membered ring systems (imidazoles, quinoxalines, 1,2,4‐triazines, pyrazines, and 1,4‐diazepines), thus linking these important heterocyclic motifs to the internal alkyne reagent space.

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“…Photochemical hydration of the C(6)ÀN(1) bond of 1,2,4-triazines has been described for 1,2,4-triazine-3,5-dione and 5-amino-1,2,4-triazin-3-ones to yield 6-hydroxy-1,2,4-triazine-3,5-dione and 5-amino-6-hydroxy-1,2,4-triazin-3-ones, respectively [301]. Chemical and photochemical induced reduction of some dihydro-1,2,4-triazines and aromatic 1,2,4-triazines have been described [302][303][304][305].…”

Section: Thermal and Photochemical Reactionsmentioning

confidence: 99%