Intramolecular photochemical

An intramolecular photochemical proton-transfer mechanism has also been postulated by W. C. Clark and G. F. Lothian [7Vans. Faraday Soc. 54, 1790 (1958)]. 

Another example of an intramolecular photochemical rearrangement occurs when 1,1,2-trimethylsilene is irradiated at 250 nm, isomerizing to vinyldimethylsilane as the result of a 1,3-H shift.26... 

This compound can be prepared by photolysis of 105, another example of an intramolecular photochemical 2 + 2 cycloaddition Lemal Lokcnsgard J. Am. Chem. Soc. 1966,88, 5934 Schafer Criegee Askani Griiner Angew. Chem. Ml. Ed. Engl. 1967, 6, 78 [Angew. Chem. 79, 54]. 

Intramolecular photochemical reactions need the presence of light sensitive groups such as carbonyls to induce transformations by oc-cleavage (Norrish I reaction) or by y-H-abstraction (Norrish II reaction). 

Since all of the model compounds examined were monomeric lignin-like structures, our current studies do not address the possibility of an intramolecular photochemical initiated reaction contributing to brightness reversion. Investigations directed at examining this latter issue are ongoing. 

Dilling, W. L. Intramolecular photochemical cycloaddition reactions of nonconjugated olefins. Chem. Rev. 66, 373 (1966). 

The uranyl ion luminesces in fluid solutions at room temperature2 201 202 thus providing a tool for the study of bimolecular excited state processes. In several cases, however, this study is complicated by the fact that the uranyl ion forms complexes with a variety of chemical species, so that it is often difficult to distinguish between intramolecular photochemical processes involving uranyl ion-ligand complexes and intermolecular photochemical processes involving reaction between an electronically excited UO + species and the substrate2,201,202 ... 

Brumfield, M.A. and Agosta, W.C. (1988) Two triplets mediating intramolecular photochemical abstraction ofhydrogen by nitrogen in 4-acyl-6-alkylpyrimidines. Journal of the American Chemical Society, 110 (20), 6790-6794. 

Hoffmann, N. and Pete, J.-P. (1995) Intramolecular photochemical reactions of 3-Alkenyloxyphenols. Tetrahedron Letters, 36, 2623-2626. 

Shinto, T., Tajima, f., Suishu, T., and Somekawa, K. (1991) Intramolecular photochemical reactions of 4-(alkoxycarbonyl group at the olefinic carbon chain. Journal of Organic Chemistry, 56, 7150-7154. 

The details of the above process have been refined somewhat by subsequent flash photolysis studies [34-38]. However, in all of the mechanisms that have been discussed, a Fe(III)-oxalate complex is reduced by an intramolecular photochemical process, generating an unbound radical (either C204 or C02 ). If a C2(),r radical is produced, it rapidly decomposes to form C02- [39] ... 

A Fe(III)-carboxylate complex is reduced by an intramolecular photochemical process. This produces a radical that can reduce a second Fe(III)-carboxylate complex. 

The intramolecular photochemical [2+2] cycloaddition of bicyclo[3.3.0]octa. dienes has been examined by several groups.128 197, 99) A striking example of a synthetic application of this chemistry is given in Scheme 22. 

Heathcock used as concerted cycloaddition intramolecular photochemical (2 + 2) addition to create the quaternary center in his projected synthesis. A cationic rearrangement Wagner-Meerwein rearrangement) was intended as further key step but failed (162). 

During the synthesis of the Woodward reserpine precursor (17 Scheme 4), Peailman used the protected acylacetal (13) to control the stereochemistry of an intramolecular photochemical cycloaddition to (14). The strategy for opening the cyclobutane ring employed the Baeyer-Villiger reaction to convert the 7-keto ester (15) to a 3-hydroxy ester (16), which underwent retroaldolization to (17). 

Although not strictly belonging to this section, the case of diastereoselective, intramolecular photochemical /1-lactone formation from a-phenylcinnamic acid will be mentioned. When either (E)-l or (Z)-7 was irradiated, c . -3,4-diphenyl-2-oxetanone rac-9 was obtained in good yield 25. The reaction was assumed to yield first the hydroxy oxetene rac-8, which then selectively tautomerizes to the crs-product rue-925. 

These imidazolidinones are also photoreactive, yielding phenanthrenes. Intramolecular photochemical hydrogen abstraction within the analogous thio-compounds (255) yields the cyclized products (256). Intramolecular hyd-... 

An efficient route to the synthesis of the cycloalkanones (37) involving the intramolecular photochemical cyclization of the enones (38) has been described. This yields the tricyclic... 

Irradiation of the diane (127) yields the cyolobutane derivative (128) as the sole product. The structure of this was confirmed by X-ray analysis. Prinzbach at aJ. have reported the intramolecular photochemical (2-I-2)-addition of the dienes (129) to afford the adducts (130). Cycloaddition is also reported to take place on irradiation of the benzene derivatives (131) where the adducts were isolated as Diels-Alder adducts of the dienes (132). Acetone-sensitized irradiation of the diene (133) results in the rapid conversion... 

Ortho addition to the arene ring also occurs in cage systems where geometrical constraints disallow other orientations of addition a common example is the intramolecular photochemical cycloaddition which can occur in... 

Dzakpasu, A. A., Phillips, S. E. V., Scheffer, J. R., and Trotter, J. Intramolecular photochemical hydrogen abstraction reactions in the solid state. Correlation with X-ray crystal structure data. J. Amer. Chem. Soc. 98, 6049-6051 (1976). Trotter, J. Structural aspects of the solid-state photochemistry of tetrahydron-aphthoquinones. Acta Cryst. B39, 373-381 (1983). 

In the laboratory of H. Hiemstra, the synthesis of the bicyclo[2.1.1]hexane substructure of solanoeclepin A was undertaken utilizing the intramolecular photochemical dioxenone-alkene [2+2] cycloaddition reaction. The dioxenone precursor was prepared from the commercially available fert-butyl acetoacetate using the acetoacetic ester synthesis. When this dioxenone precursor was subjected to irradiation at 300 nm, complete conversion of the starting material was observed after about 4h, and the expected cycloadduct was formed in acceptable yield. 

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