Photodeconjugation

Buffer catalysis has been applied to induce chiral induction by enantio-selective protonation remarkable enantiomeric excess was achieved in the photodeconjugation of a,/3-unsaturated ketones and esters by using chiral catalysts for the ketonization of photoenols in aprotic solvents.29... 

Accordingly, apolar solvents, in particular n-hexane and dichloromethane, were found to be convenient for these enantioselective photodeconjugation reactions. 

For a complementary approach of asymmetric photodeconjugation to yield secondary stereogenic centers containing fluorine F. Bargiggia, S. Dos Santos, O. Piva, Synthesis 2002, 427-437. 

The reactivity and selectivity trends described for the intermolecular version of the Paterno-Biichi reaction are also valid for the intramolecular version. Special aspects of intramolecular photocycloadditions have been reviewed [157]. A crucial role for the reactivity mode of unsaturated carbonyl compounds is the tether length, i.e., the distance between reactive carbonyl and C-C double bond. Conjugated systems, i.e., oc,(3-unsaturated carbonyls, prefer photodeconjugation or photocycloaddition invovling the C-C double... 

The interesting pyranone (1) has been obtained by photodecarboxylation of (2) using low-temperature matrix isolation techniques (Bleasdale et al.). Bart-nik et al. have described a simple photodecarboxylation route to azabicyc-lobutanes such as (3). Attention is drawn to a new photochemical synthesis of p-lactones (Aoyama et al.) and -lactams (see ref. 50 in Part III, Chapter 2). Skinner and Weedon have reported an interesting method for photodeconjugation of a,p-unsaturated esters e.g., (4) (5). Polar solvents are required,... 

The amide (38a) is photochemically inert on irradiation in ether. The related compound (38b) is, however, photochemically reactive and undergoes fission by a Norrish Type II process to yield a mixture of products.The results of a study of the enantioselective photodeconjugation reactions of the lactones (39) have been published. The behaviour of the ketones (40) and (41) in the isotropic and the two solid phases of heneicosane (CcxH ) has been evaluated. The influence of the various phases on the ratio of elimination to cyclization products of the ketones was discussed. The modification of the photoreactivity of ketones (42) in cyclodextrin has been... 

A study of the photodeconjugation reaction of the ester (136) in the presence of a variety of optically active amines such as (IR,2S)-l-phenyl-2-isopropylamino propanol has shown that the product can be obtained with an enantiomeric excess of about 70 X. Irradiation of the alkynylketones (137) in alcohols (methanol, ethanol or propanol) affords the furan derivatives (138) by a free radical hydrogen abstraction path. Excitation of the cyclohexenone derivatives (139) yields the cyclized products (140) the structures of which were verified by X-ray crystallography. The formation of the amide products is reminiscent of a Norrish Type II process. 

Henin, F., Mortezaei, R., Muzart, J., Pete, J.-P, and Piva, O., Enantioselective photodeconjugation of conjugated esters and lactones in the presence of ephedrine. Tetrahedron, 45, 6171, 1989,... 

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