Pyridine photochemical reaction

Paal-Knorr synthesis, 4, 118, 329 Pariser-Parr-Pople approach, 4, 157 PE spectroscopy, 4, 24, 188-189 photoaddition reactions with aliphatic aldehydes and ketones, 4, 232 photochemical reactions, 4, 67, 201-205 with aliphatic carbonyl compounds, 4, 268 with dimethyl acetylenedicarboxylate, 4, 268 Piloty synthesis, 4, 345 Piloty-Robinson synthesis, 4, 110-111 polymers, 273-274, 295, 301, 302 applications, 4, 376 polymethylation, 4, 224 N-protected, 4, 238 palladation, 4, 83 protonation, 4, 46, 47, 206 pyridazine synthesis from, 3, 52 pyridine complexes NMR, 4, 165... 

Photochemical cycloadditions of furans have also been reported occasionally. The photochemical reaction of furan and 3-cyano-2-methoxypyridines (in benzene solution) results in the formation of 1 1 adducts 16 and 17 (accompanied by a transpositional pyridine and a pyridine dimer) <99JCS(P1)171>. 

Diazocine is an unstable yellow oil. The 2,4,6,8-tetraene structure (173) is established by the NMR spectra, which show the presence of a single species and are consistent with a tub conformation of (173) and not the double bond isomer (174). Information on the chemistry of (173) is limited. Thermolysis gives mixtures of pyridine and benzene, with approximately equal rates and activation parameters lower temperatures favor pyridine. Photolysis, however, either direct or sensitized, gives exclusively benzene. No pyridazine is detected in either thermal or photochemical reactions. 

The formation of benzene and pyridine presumably occurs via the bicyclo[4.2.0] valence isomers (175) and (176), although adducts of these structures with dienophiles were not obtained on heating or during irradiation. The difference in products in thermal and photochemical reactions could be explained either by interconversion of (173) and (174) and rate-limiting isomerizations of (173) to (176) and (174) to (175), or alternatively, rate-limiting isomerization of (173) to (174) and symmetry-allowed 4ir photocyclization of (173) to (175) (79JOC1264). 

Following a newly discovered indole synthesis, it has been shown that photochemical reaction of acetone anion with 3-amino-2-chloropyridine in liquid ammonia gives 2-methylpyrrolo[3,2-6]pyridine in 45% yield (80JOC1546). 

The conversion of 33 oto to 33 is performed in two steps 1) substitution of py by DMSO ana isomerisation, 2) substitution of DMSO by py. Its overall yield is above 80%. In order to perform a complete cycle, the photochemical reaction leading back to 33p oto was carried out in the usual way (irradiation performed at room temperature with a 1000 W xenon arc-lamp filtered by a water filter) in pyridine. It turned out to be virtually quantitative. 

An ET mechanism is involved in the photochemical reaction of 2- and 4-cyanopiridine and other cyanoazines with alcohols, alkenes, or amines substitution products are usually obtained. As an example, allylpyridines (and quinolines) are obtained from the acetone-sensitized reaction of the corresponding cyanohetero-cycles in the presence of alkenes (Scheme 53). The reactions of various dicyano-pyridines have also been studied in detail and the distribution of the products obtained is well rationalized with an ET mechanism [168]. 

Wood et compared cold-deposited films of silver (on copper at 100 K) to bulk-roughened surfaces (by a photochemical reaction with iodine). They found that the enhancement on the former was about 5 times larger than on the latter. They also found that with equal exposures to pyridine the evaporated films exhibited predominantly a first-layer enhancement, while the roughened surface showed comparable signals from the first and subsequent layers. These conclusions strongly depend on the absolute coverages on the surfaces and the relative coverages of the two systems studied, both of which are not known precisely. 

Benzene still provides fruitful labour for the dedicated photochemist. A three photon excitation study of the So(A, ) - SjfBju) transition in the neat liquid shows that under this condition internal states exist which make the experimentally observed 3 photon allowed pathway. A photochemical study of both benzene and pyridine shows that Dewar benzene structure formation involves S1-S2 state mixing by irradiation at 253.7 nm. For pyridine in a xenon matrix all photochemical reactions are quenched and evidence for the formation triplet state of this molecule is produced for the first time. The photophysical significance of PE surface geometries of the low... 

As a possible in-vitro model for one-electron transfer in photosynthesis, the photochemical reaction between hemin and Chla in pyridine solution has been studied, and it has been shown that the relatively slow reduction and oxidation of iron porphyrins can be accelerated by the presence of Chla by an order of magnitude and that light further increases the rate or reaction. Chla probably forms a rather stable complex with hemin, as is shown by fluorescence quenching experiments [Brody (17)]. 

Figure 16. Excitation energy dependence of nonradiative decay rates in vapor-phase pyridine, pyrazine, and pyrimidine. The dashed lines represent S, - T intersystem crossing, whereas the solid lines represent the second nonradiative process attributed to photochemical reaction. (From ref. [11] with permission.)...

Solvent effects in the photochemical reaction of A -(2-phenyl-4-penten-l-oxy)-pyridine-2(l//)-thione and Bu3SnH have been studied [36]. Neither the use of tert-butyl benzene, chlorobenzene, bromobenzene, anisole, cyclohexane, tetrahydrofuran, nor ethanol leads to a significant change in yields and selectivities for the formation of 2-methyl-4-phenyl tetrahydrofuran (16) (50-70%, cis/trans 88 12),... 

The reaction between the PtCh ion and alkanes can be induced by irradiation [26]. When a solution of hexachloroplatinic acid and n-hexane in acetic acid is irradiated by light (A > 300 nm) [26a,c,d] or y-quanta [26b], a 7t-coinplex of hex-1-ene with platinum(II) is formed in addition to isomeric chlorohexanes. This complex has been isolated in the form of the pyridine adduct, (hex-l-cne)PtCl2Py. The yield of the it-complex in the y-induced reaction reaches 17% based on Pt. The photochemical reaction is of first order with respect to hexane. It is interesting that the photochemical reaction with hex-2-ene affords the n-complex ofhex-l-ene (Scheme VII.5). This complex can be also prepared by the reaction ofhex-l-ene with PtCL, " under irradiation. It should be noted that the photoinduced reaction of PtCl6 or PtCU with olefins is a convenient method for the synthesis of various n-o efin complexes of platinum(II) [27]. The photostimulated reaction of PtCU with stilbene does not occur, possibly due to steric restrictions. 

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