Fragmentation of Organosulphur Compounds

Photofragmentation of the cyclic tetrasulphide (119) in benzene in the presence of norbornene affords the 1,4-dithiin (120), presumably by way of the initially formed 1,2-dithione (121).  

2-Selenoxothione derivatives can be generated in a similar manner from 1,2,3,4-tetrathia-5-selenepines. Carbon-sulphur bond homolysis is commonly observed in the photochemistry of sulphur-containing 

1-oxides, and a new procedure for the reductive photodesulphon-ylation of 8-keto sulphides has been developed. Irradiation of the steroidal dienol triflate (136) in pyridine results in loss of 

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. 

Benzobenzvalene (100) has been shown to add sulphur dioxide to give the sulphone (101) and the 7-sultine (102) both adducts extrude sulphur dioxide on direct photolysis regenerating benzobenzvalene accompanied by naphthalene. Competing homolytic and heterolytic bond cleavages have been observed in singlet excited triarylsulphonium salts, and intramolecular electron transfer is involved in the photodissociation of p-nitrobenzyl 9,10-dimethoxy-anthracene-2-sulphonate.A photochemical method for the detosyl-ation of sulphonamides has been described,and the thermolysis and photolysis of some thiourea derivatives have been compared. 

Carbon-sulphur bond homolysis is responsible for many photochemi- 

Aryl phenacyl sulphides undergo carbon-sulphur bond homolysis on 

---