Pyridinium N-ylides

Photochemistry as a Tool in Heterocyclic Synthesis From Pyridinium N-Ylides to Diazepins and Beyond J. Streith, Heterocycles, 1977, 6, 2021-2043. 

Streith, J. (1977) Photochemistry as a tool in heterocyclic synthesis from pyridinium N-ylides to diazepines and beyond. Heterocycles, 6 (9), 1513-1519. 

In addition to direct insertion of perfluorinated gronp at position 1, there are plenty of methods how to introduce such a group via cycloaddition reaction. Thus, convenient method to perfluoroalkylated indolizinyl-phosphonates 31 was reported [19]. The reaction proceeded regioselectively via the 1,3-cycloaddition of pyridinium N-ylide and perflnoroalkynyl phosphonate in 49-77 % yields. Similar reaction was proposed to obtain pyrrolo[l,2-a]isoquinolinyl phosphonates in 48-78 % yields [20]. 

In the presence of K2CO3 and EtsN, pyridinium N-ylides, generated in situ from their halides, reacted with gaseous fluoroalkenes CF2=CFX (X=C1, Br) in DMF under atmospheric pressure in normal glassware at 70 °C to give the corresponding 1,2-fluorinated indolizines. Similar results were obtained with tetrafluoroethene in an autoclave [30],... 

Useful ring expansion reactions occur in the photo-Beckmann rearrangements, the photolysis of aromatic N-oxides and pyridinium N-ylides, and in the photochemical rearrangement of N-alkylphthalimides. ... 

Thermolysis of 1-imidoyliminopyridinium N-ylides 109 gave the pyrido-triazines 110 in addition to 111 and 112 (76CL413 77JOC443). Compounds 109 were obtained by the reaction of pyridinium salts 107 with 108. 

Reaction of an activated halogenoazole toward S Ar gives the N-benzimidazolylpyridinium salts 54 (66TL3369) [Eq.(l)j. In the same way, using the 2-chlorobenzimidazole 59 directly produced the N-ylide 61, which was in turn transformed to the pyridinium salt 60 in acidic media [70ZN(B)954][Eq.(4), Table V]. Moreover, reaction of the 2-chloro-benzimidazole 62 with pyridines gave the N-ylides 64 (75KGS987) [Eq.(4), Table Vj. 

Pyridinium ylides and related species are known to undergo analogous photoreactions. The cycloalkane-annulated pyridinium N-aminide (54 n=2) is converted in this way, presumably via the diaziridine (55), into the cyclopenta[ ]-1,2-diazepine (56). A competing 1,5-electrocyclization is preferred, however, on irradiation of the N-aminides (54 n=3 or 4) and leads to the 3-azaquinolizinones (57 n=3 or 4) by the pathway shown in Scheme 4. The spirobenzylisoquinoline (58) has been prepared by irradiation of the oxide (59)the likely pathway is shown in Scheme 5. 

One Nitrogen Atom (it is self-subdivided into Pyridines, Pyridinium Compounds, Ylides, Pyridine N-Oxides, Applications of Pyridines, Bipyridines and Related Systems, Hydropyridines, Biologically Active Pyridines and Hydropyridines, Pyridines Annulated with Carbocycles, Pyridines Annulated with Heterocycles). 

The isoelectronic pyridinium A-ylides, e.g. 110, behave in an analogous manner to the A-oxides. Photolysis in an inert solvent leads to the diazepine 112 as the sole product, probably with intermediate formation of a diaziridine 111, followed by electrocyclic N/C-1 cleavage. Photolysis in benzene yields, in addition to the diazepine 112, the azepine 113 because of a competitive N-N cleavage and interaction of the solvent with the resulting nitrene (by a [2+1] cycloaddition and electrocyclic opening of the diazanorcaradiene) ... 

Preparation of new nitrogen-bridged heterocycles using pyridinium salts and N-ylides 05Y222. 

N-Arylations of several other heterocycles have also been accomplished, including mono- and diarylation of imidazoles to form N-aryl imidazoles and imidazolium ions, respectively, which was extended to the synthesis of bis (N-heterocyclic) ligands [101, 102]. Pyridinium triazolinone ylides were obtained by a one-pot copper-catalyzed carboxygenation and chemoselective N-arylation of triazolopyridines with aryl(mesityl)iodonium salts (Scheme 6a) [103]. 

Strub, H., Strehler, C., and Streith, J., Photoinduced nitrene, carbene and atomic oxygen transfer reaction starting from the corresponding pyridinium N-, C- and 0-ylides, Chem. Ber., 120, 355, 1987. 

Pyridinium ylide, 1-ethoxycarbonylimino-photolysis, 2, 313 Pyridinium ylide, N-imino-photolysis, 2, 314 synthesis, 2, 185 Pyridinium ylides, 2, 336 photolysis, 2, 313-314 Pyridin-2-one, 3-acetyl-synthesis... 

Tlie existence of the ylide 19, which can formally be interpreted as the deprotonation product from the corresponding salt 7a, has been claimed by trapping chlorocarbene with pyridine during the laser-flash photolysis of e do-7-chlorodibenzo[n,c]bicyclo[4.1.0]heptane (18) (96JPC18426). Bromination of l-vinyl-2-pyridone (20) yields the bicyclic pyridinium bro-... 

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