82248-72-4Relevant academic research and scientific papers
Ylide Formation and Rearrangement in the Thermal Reaction of 6H-Dibenzothiopyran and its 6-Phenyl Derivative with Diazoalkanes
Benati, Luisa,Montevecchi, P. Carlo,Spagnolo, Piero
, p. 917 - 922 (2007/10/02)
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).
