79249-49-3

Upstream product

• 273-77-8 benzo[1,2,3]thiadiazole 
• 908093-98-1 diazodiphenylmethane 
• 79249-48-2 6-phenyl-6H-dibenzo[b,d]thiopyran 
• 90-99-3 diphenylchloromethane 

Relevant academic research and scientific papers

Ylide Formation and Rearrangement in the Thermal Reaction of 6H-Dibenzothiopyran and its 6-Phenyl Derivative with Diazoalkanes

Reaction of 6-phenyl-6H-dibenzothiopyran (1b) with diphenyldiazomethane (2a) in refluxing benzene affords 6,6,7-triphenyl-6,7-dihydrodibenzothiepin (3b) as major product, together with minor amounts of 6-diphenylmethyl-6-phenyl-6H-dibenzothiopyran (4b).Analogous results are obtained from the reaction of 6H-dibenzothiopyran (1a); however, in this case the yields of the corresponding ring-expansion and insertion products (3a) and (4a) are similar.Copper(II) sulphate-catalysed thermal decomposition of ethyl diazoacetate (2b) in the presence of (1b) yields mainly ethyl 6-phenyl-6H-dibenzothiopyran-6-ylacetate (4d), together with minor amounts of (probably) 6-ethoxycarbonyl-7-phenyl-6,7-dihydrodibenzothiepin (3d), but only the product of insertion of ethoxycarbonylcarbene into the C(6)-H bond, i.e. (4c), is observed from the reaction of (2b) with (1a).Formation of the products (3) and (4) is rationalized in terms of a thermal ylide exchange reaction of the unstable sulphonium ylides (7a-d), initially produced in competition with a Stevens-type rearrangement.In support of the above mechanism, pyrolysis of the stable 6H-dibenzothiopyran-5-io(bismethoxycarbonyl)methanide (7e) gave only the product of insertion of bismethoxycarbonylcarbene into the C(6)-H bond, i.e. the malonate (4e), whereas almost exclusive formation of the ring-expansion product (3f) occured on pyrolysis of the 6-phenyl derivative of the ylide (7e).

Reactivity of Triplet Diphenylcarbene towards the Sulphur Atom of 1,2,3-Benzothiazole

Thermal decomposition of diphenyldiazomethane (1) at 87 deg C in chlorobenzene in the presence of 1,2,3-benzothiadiazole (2) afforded 9-phenylthioxanthen (3), 6-phenyl-6H-dibenzothiopyran (4), 6-benzhydryl-6-phenyl-6H-dibenzothiopyran (5) and thianthren (6).Reaction products are explained in terms of attack on the sulphur atom of (2) by triplet diphenylcarbene, leading to decomposition of the heterocyclic nucleus with loss of nitrogen and formation of a diradical intermediate (7), from which products (3)-(6) can arise.Some evidence is presented that benzothiadiazole (2) may act as an an effective spin-trap for triplet diphenylcarbene, thus preventing reversible interconversion of singlet and triplet states.