Photoinduced cyclization

An intramolecular 2,2 -couphng in certain l,2-bis(indol-3-yl)ethenes has been reported to occur on irradiation, e.g., leading to the indolocarbazole 39 after photoinduced cyclization of the E) compound 40 (Scheme 7). The substrate 40... 

Certain substituted p-quinones undergo photoinduced cyclization to give a benzo-fused oxygen heterocycle as a result of n->v ... 

Photoinduced cyclizations of phenyl triphenylsilyl thioketone (156) with cis- and fraws-l,2-dichloroethene give a mixture of silyl thietanes 157 and 158 in a regio- and stereoselective manner (equation 66)207. These reactions involving biradical intermediates and ring closure are governed by the steric effect. The steric hindrance between the Ph3Si group and the vicinal chlorine atom ensures their trans relationship in the thietane products. 

Other photoinduced cyclization reactions can occur by conrotatory bond formation to give the 9 PjIO P-antiisomers, isopyrocalciferol2 [474-70-4] (23) or isopyrocalciferol [10346-44-8] (24) (Fig. 5), whereas thermal cyclization at >100 C leads to the two 9,10-syn isomers, (9a,10 a)-pyrocalciferol (27)... 

Keywords Metallo-Siloxanes / Photoinduced Cyclization / Photoinduced Metallation... 

Ps laser photolysis studies of the photochromism of a furylfulgide shows that photoinduced cyclization occurs within 10 ps °. 

Acid Catalyzed Rearrangements. An example of a photoresist based on an acid catalyzed rearrangement is the diaryliodonium salt photoinduced cyclization of cis-1,4-polyisoprene shown in Equation 18. This facile cyclization which has been reported previously (11) by non-photochemical processes results in a polycyclic polymer whose physical properties and solubility characteristics are considerably different than the initial polymer. Exploitation of these differences in the exposed and unexposed regions of the polymer film permit their use as either positive or negative tone resists. 

Investigation of the temperature dependence of the photochemistry of o-methylacetophenone has revealed that the rate of decay of the biradical generated in the photoenolization is associated with a low A factor. An explanation for the effect lies in the requirement for spin inversion in the process. The key step in a newly developed synthesis of ( )-oestrone is the photoinduced cyclization (1) (2). Excitation of (1) induces photoenolization to the kinetically... 

Azomethane imines undergo an analogous photoinduced cyclization to give diaziridines. The dihydroisoquinoline derivative (99), for example, is converted on irradiation in cyclohexane or benzene into the diaziridine (100) the transformation is thermally reversible. In contrast, the pyrazolidinone azomethine imines (101) undergo photoreversible conversion into the diaziridines (102), providing in this way a useful reversible photochromic system. The analogous photoisomerization of a pyrene-substituted pyrazolidinone azomethinimine has... 

A full account of the synthesis of indolin-2-ones and 1,4-dihydro-3(2H)-isoquinolinones by photoinduced cyclization of -acy1-o-chloroanillnes or N-acyl- -chlorobenzylamines has also... 

The development of photochemical variants of the Bergman cyclization would contribute to the broadening of its scope and utility. However there are relatively few examples of photoinduced cyclizations, despite the promise that such an approach would have in the photodynamic therapy of cancer. Funk and co-workers reported that certain cyclic ortho-dialkynylarenes, such as 9, underwent the photo-Bergman cyclization on irradiation in Pyrex. ° In 2000 Russell and co-workers showed that 10-membered cyclic pyrimidine enediynes could undergo cyclization efficiently (82-83%) when exposed to light (310 nm) in /-PrOH for 2-24 hours. 

Yamato, T., Fujita, K., Futatsuki, K., and Tsuzuki, H., Medium-sized q clophanes. Part 53. Synthesis and conformational studies and photoinduced cyclization of syn-[n.2]metacyclophanenes, Can. J. Chem., 78,1089, 2000. 

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