P isomeric

Not all photooxidation pathways can be attributed to radical cations as the only intermediate. For example, in the benzophenone-sensitized reaction, some and P—and a—>p isomerization (in the case of a-dGuo) is observed (Vialas et al. 1999). while no such isomerization occurs upon the Mn-TMPyP-mediated oxidation by KHS05 (Vialas et al. 1999). Here, Iz is the only detected product [90% yield Vialas et al. 1998] which points to different intermediates in these two systems. Ascorbate or cysteine, may intercept G% and in their presence the oxazolone yield is strongly reduced (Douki et al. 1999). 

Substrates in which the methane carbon is not fully substituted, for example in (35 R = H), are similarly ODPM unreactive, irrespective of the ring size of the alkene moiety p,y - a,p isomerization of the C bond appears to constitute a major path of chemical energy dissipation. One exception in this category is, however, the earlier cited (3d) in which the alkene is part of a styrene moiety. ... 

When pure /ra/is-PtCUfBujP) is placed in solution with a trace of Bu,P, isomerization occurs to give a mixture of cis and trans isomers. Provide a plausible mechanism. 

The phosphitylation of a ketone through its enol form leads to the phosphorus(III) esters carrying a conjugated unsaturated carbonyl moiety their isomerization to the phosphonic diesters 603 (R = EtO) occurs reasonably readily, but other compounds in which, for example, R2P = (Pr 0)(Et2N)P, isomerize with greater difficulty, during distillation, or during an extended period at room temperature ". Other phosphite esters, 604, isomerize when heated at 160 or in the presence of a trace of metallic sodium at the same tem-perature. The formation of dialkyl (4-oxopentyl)phosphonates by similar means has also been reported. ... 

Oil of turpentine may be boiled without suffering decomposition, but if heated under pressure at 250°-t300° (482°-573° F.) the terpene is converted into two products, one liquid, boiling at 177° (330°. 8 P.), isomeric with the terpene, called isoterehenthene the other viscous, boiling at about 400° (753° F.), polymeric with the first, C20H32, called metaterebenthene. 

DeTtsova, D.P. Gambaryan, N.P. Isomerization of a perfluoro-a-lactam to a substituted carbamoyl fluoride. Izv. Akad. Nauk SSSR, Ser. Khim. 1984, 1367. 

In a related fashion, asymmetric amination of ( )-cinnamic acid yields L-phenylalanine using L-phenylalanine ammonia lyase [EC 4,3,1,5] at a capacity of 10,000 t/year [1274, 1601], A fascinating variant of this biotransformation consists in the use of phenylalanine aminomutase from Taxus chinensis (yew tree), which interconverts ot- to p-phenylalanine in the biochemical route leading to the side chain of taxol [1602], In contrast to the majority of the cofactor-independent C-0 and C-N lyases discussed above, its activity depends on the protein-derived internal cofactor 5-methylene-3,5-dihydroimidazol-4-one (MIO) [1603], Since the reversible a,p-isomerization proceeds via ( )-cinnamic acid as achiral intermediate, the latter can be used as substrate for the amination reaction. Most remarkably, the ratio of a- vs, 3-amino acid produced (which is 1 1 for the natural substrate, R = H) strongly depends on the type and the position of substituents on the aryl moiety While o-substituents favor the formation of a-phenylalanine derivatives, / -substituted substrates predominantly lead to p-amino analogs, A gradual switch between both pathways occurred with m-substituted compounds. With few exceptions, the stereoselectivity remained exceUent (Scheme 2,215) [1604, 1605],... 

The name bisabolol includes both a- und p-isomeres of this compound, with each existing in two enantiomeric forms. In nature, the most common form is... 

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