2-Nitrobenzyl carbonates, photochemical

The incorporation of the additional methylene unit serves to substantially increase the rate of photochemical deprotection vs o-nitrobenzyl carbonate. Introduction of an additional methyl group in the a-position further increase the rate of deprotection. ... 

Evidence has been obtained that the photodecarboxylation of benzannelated acetic acids in aqueous solution proceeds via carbanion intermediates 5H-dibenzo[a,d]cyclohepten-5-carboxyl-ic acid, for example, undergoes photodecarboxylation with a quantum efficiency of close to unity. The reactions of the -nitrobenzyl anion, generated by photochemically induced loss of carbon dioxide from -nitrophenylacetate anion, have been examined and a mechanism proposed to account for the formation of the corresponding bibenzyl derivative. Reductive decarboxylation of carboxylic... 

Ethylene and thioformaldehyde are the products of irradiation of matrix-isolated thietane at lOK. Sulphur-carbon bond homolysis has also been observed on irradiation of the nucleoside membrane transport inhibitor, 6-[ (4-nitrobenzyl) thio] -9- (/8-D-ribofuranosyl) -purine (94), and the oxazolidin-2-one (95) has been converted into the allyl derivative (96) by photochemically induced radical allylation.Efficient conversion of cyclic thioacetals into the corresponding carbonyl compounds under neutral conditions has been achieved by 2,4,6-triphenylpyrylium tetrafluoroborate-sensitised irradiation in moist dichloromethane,and diaryl sulphides and the corresponding sulphoxides and sulphones have been reported to undergo anion-promoted carbon-sulphur bond photocleavageboth processes appear to involve an initial electron transfer. Sulphur-hydrogen bond horaolysis has been reported in t-butanethiol and is also responsible for the photoinitiated thiylation of fluorobromoethylenes and of trialkylethynylsilanes and t-butylacetylene. 

The orffto-nitrobenzyl chromophore has also been employed for phosphate deprotection but, as in Eq. (12) for amides, this photochemistry again does not result from excited state carbon-oxygen bond cleavage [126,128]. Similarly, de-syl phosphates like 89 release phosphate photochemically but, as discussed in Sec. IV.D.3, by a pathway beginning with n,n excited state of the carbonyl group [13,126,129]. 

The photochemical cleavage of the phosphorus-carbon bond in many benzylic phosphonic acids occurs through intramolecular electron transfer and gives monomeric metaphosphate together with substituted toluenes and, in many cases, 1,2-diarylethanes. The ultraviolet irradiation of (4-nitrobenzyl)phosphonic acid dianion in solution in aqueous ethanol yields l,2-bis(4-nitrophenyl)ethane, 4-nitrotoluene, H3PO4 and monoethyl phosphate (Scheme Irradiation of the same acid in the presence of dbu (other tertiary... 

In the caged ATP structure of Section 16.3.9, a methyl group is added to the benzylie carbon of the nitrobenzyl group. Why should this increase photochemical efficiency ... 

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