Carbon photoinitiated carbonylations

Unfortunately, the use of palladiiun(0)-catalyzed carbonylation reactions in carbon-11 chemistry is restricted by problems related to the competing /3-hydride elimination for electrophiles bearing a hydrogen in the j8-position. In order to overcome this restriction, uncatalyzed photoinitiated carbonylation reactions have been more closely investigated using alkyl iodides, amines and alcohols as precursors. The first results were promising, providing esters and amides in the majority of cases in radiochemical yields of 40-70% as indicated for the examples 50-55 ... 

Figure 5.21 Use of photoinitiated carbonylations in the synthesis of carbon-11-labeled aliphatic esters and amide...

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. 

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