Sulphur extrusion

The reaction with benzothiophens provides a route to substituted naphthalenes by thermal ring-opening and sulphur extrusion of the photoadducts (equation 80) >... 

Sulphur extrusion and biaryl formation is reported for (129) which gives (130) on irradiation in the presence of trimethyl phosphite however, the reaction fails for (131), which is recovered... 

Reactions in which a sulphur atom that bridges or interconnects two carbon groups is extruded with formation of a carbon—carbon bond between the two carbon groups is termed a sulphur extrusion reaction (equation 90). These types of reactions have proven to be of synthetic utility and are treated in this section. 

The thia[ll]annulene (5) reacts with maleic anhydride at room temperature to give the dihydrothiepin (7) as a 2 1 mixture of the exo and endo-adducts (Scheme 2). The intermediate adduct (6) iexo- and e/u o-mixture) was not isolated but its presence was demonstrated by n.m.r. spectroscopy. Dehydrogenation of the dihydrothiepin (7) was accompanied by sulphur extrusion and led eventually to the ester (9). The presence of the thiepin (8) as an intermediate was presumed on the basis of indirect evidence. 

Sulphur extrusion occurs when 2-phenyl-4-methylthiobenzo[6]-l,4-thiazepine (21) is refluxed in propan-2-ol containing morpholine. Formation of the product (23) is accounted for by the sequence (21) (22) -> (23)... 

Cyclophanes. Many reports have appeared relating to these compounds. Most of them describe their synthesis, either by the sulphur-extrusion process reported several times in earlier sections or by some form of cycloaddition reaction. 

Among those obtained by C—C bond formation resulting from sulphur extrusion is the compound (423), in which the benzene rings are perpendicular to each other,the [3.3]paracyclophanes (424), the electronic spectra of which have been described, and (425), used for comparison of ring strain and... 

Labelling studies ( 0) on the thermal cyclization of o-benzamidobenzoic acid to 2-phenyl-3,l-benzoxazin-4-one (320 R = Ph) reveal that oxygen is lost with equal probability from the CO2H and COPh groups.3,l-Benzoxazin-4-ones (320 R = Me or Ph) are the products of a remarkable ring-expansion, sulphur-extrusion process undergone by 0-acyl-2,l-benzisothiazolones (321 R = Me or Ph) in hot pyridine solution (Scheme 76). ... 

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