Photooxygenation reactions

Pkotoehemical ene reactions. Photooxygenation of 1,3-choIestadiene (1) does not lead to the expected endoperoxide, but to A -cholestadienone-3 as the major product (equation I). Similarly, photooxygenation of 6,ll-/S/f-eudesma-l,3-diene-6,13-olide (1) gives the hydroperoxide (2) and hyposantonin (3), which undoubtedly is formed from (2) (equation II). In both examples, the ene reaction is... 

Brilnker, H.-G. and Adam, W., Diastereoselective and regioselective singlet oxygen ene oxyfunc-tionalization (Schenck reaction) photooxygenation of allylic amines and their acyl derivatives,/. Am. Chem. Soc., 117, 3976,1995. 

Protoporphyrin-IX, N-methyl-, 4, 396 Protoporphyrins, 4, 382 photooxygenation, 4, 402 Prototropic tautomerism polyheteroatom six-membered rings, 3, 1055 Prozapine properties, 7, 545 Pschorr reaction carbolines from, 4, 523 dibenzazepines from, 7, 533 dibenzothiophenes from, 4, 107 phenanthridines from, 2, 433 Pseudilin, pentabromo-synthesis, 1, 449 Pseudoazulene synthesis, 4, 526 Pseudobases in synthesis reviews, 1, 62 Pseudocyanines, 2, 331 Pseudothiohydantoin synthesis, 6, 296 Pseudouracil structure, 3, 68 Pseudoyangonin IR spectra, 3, 596 Pseudoyohimbine synthesis, 2, 271 Psicofuranine biological activity, 5, 603 as pharmaceutical, 1, 153, 160... 

In the synthesis of carpamic acid (98), Mitsutaka and Ogawa have used 1,2-dihydropyridine as a starting material [80H(14)169]. Photooxygenation of dihydropyridine 8h afforded enr/o-peroxide 96. Subsequent stereoselective nucleophilic reaction of 96 with ethyl vinyl ether in the presence of tin chloride gave tetrahydropyridinol 97, which was then converted into carpamic acid (98) in six more steps. 

In a different type of reaction, alkenes are photooxygenated (with singlet O2, see 14-8) in the presence of a Ti, V, or Mo complex to give epoxy alcohols formally derived from allylic hydroxylation followed by epoxidation, for example, ... 

In the photooxygenation of electron-rich olefins with allylic hydrogen atoms, ene reactivity usually dominates [96]. Nevertheless, other reactions become the preferred reaction mode. Inagaki et al. [92] attributed the exclusive [2h-2] cycloaddition... 

The photooxygenation of chiral l,2-dihydronaphthalene-2-carboxylic acids leads to a mixture of the diendoperoxide (37) and hydroperoxide (38) arising from a double [4+2] cycloaddition and an ene reaction, respectively <96CC2585>. 

Some unusual pyridazine syntheses were reported. A dye-sensitized photooxygenation reaction of ribofuranosyl furans gave a new entry to pyridazine C-nucleosides 14... 

Conventional singlet oxygen sensitizers such as Thiazine dyes, 2 and 3, have been reported to promote Wagnerova Class II electron-transfer photooxygenations.60 For example, the participation of singlet oxygen in the reaction depicted in Fig. 9... 

A striking feature of the intrazeolite singlet oxygen ene reaction is the rate enhancement often observed in these reactions.57,67 This rate enhancement is nicely accounted for by stabilization of the incipient perepoxide as depicted by Model C in Fig. 12. This rate enhancement can be used to promote the ene reaction at the expense of other reaction modes.68 An interesting example of this was reported by Stratakis and Rabalakos.69 Photooxygenations of alkenylarenes, 11 and 12 (Fig. 15) are dominated by [2 + 2] and [4 + 2] reactions in solution but react predominately by the ene mode in intrazeolite reactions. 

The majority of intrazeolite photooxygenations have been conducted in NaY,84 85 however, one study in the pentasil zeolite ZSM-5 demonstrates that steric confinement effects can play important roles.84 A comparison of the reactions of a series of tri-substituted alkenes in isooctane, NaY, and in ZSM-5 is given in Fig. 21. The reactions... 

The most notable feature of these intrazeolite photooxygenations (Fig. 30) is that the oxygen CT band experiences a dramatic bathochromic shift in comparison to solution. This was detected initially by recording the product growth as a function of irradiation wavelength (laser reaction excitation spectrum)98,110 and was later verified by direct observation using diffuse reflectance UV-Vis spectroscopy.111 For example, 2,3-dimethyl-2-butene CT-absorbance is shifted to lower energy by more than 300 nm... 

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