Cu(OTf)₂-mediated C(sp²)–H arylsulfonylation of enamides via the insertion of sulfur dioxide

Abstract

A stereoselective Cu(OTf)2-mediated C(sp2)–H sulfonylation of enamides with arylsulfonyl radicals generated in situ from DABSO and diazonium salts is developed.

Direct C(sp2)‐H Arylsulfonylation of Enamides via Iridium(III)‐Catalyzed Insertion of Sulfur Dioxide with Aryldiazonium Tetrafluoroborates

“…Notably, this transformation proceeded in a highly stereoselective manner, which afforded geometrically‐defined ( E )‐configured β‐ amidovinyl sulfones. The stereochemistry of 3 aa could be further confirmed by X‐ray crystallography …”

“…As pioneeringly disclosed by Wu and coworkers, the arylsulfonyl radicals generated in‐situ through the combination of DABSO and aryldiazonium salts, could serve as an efficient intermediate for sp 2 ‐arylsulfonylation . Recently, this synthetic strategy has been employed by our group to access the geometrically‐defined β ‐sulfonylated enamides (Scheme b) . Nevertheless, stoichiometric amount of copper(II) triflate was required to increase the reaction efficiency.…”

“…Therefore, they have gathered increasing attention among the chemical community. [1] Especially, β-amidovinyl sulfones have been considered as synthetic targets of particular interest, because they could be easily hydrolyzed to αsulfonyl ketones [2] or be reduced to bioactive chiral βamido sulfones through asymmetric hydrogenation. [3] Thus, the development of efficient and straightforward protocols to access β-amidovinyl sulfones is highly desirable.…”

“…[13] Recently, this synthetic strategy has been employed by our group to access the geometrically-defined β-sulfonylated enamides (Scheme 1b). [2] Nevertheless, stoichiometric amount of copper(II) triflate was required to increase the reaction efficiency. In order to overcome this limitation, we herein reported an iridium-catalyzed C(sp 2 )À H sulfonylation of enamides with DABSO and diazonium salts to furnish synthetically valuable β-amidovinyl sulfones in excellent yields and stereoselectivities (Scheme 1c).…”

“…The stereochemistry of 3 aa could be further confirmed by X-ray crystallography. [2] Next, we started to investigate the substrate scopes with respect to enamides. As shown in Table 3, the variation of electronic or steric peculiarities on the αphenyl group of enamides did not show dramatic effect to the reaction efficiency and stereoselectivity, allowing the formation of geometrically-defined β-amidovinyl sulfones 3 ba-3 ja in 57-91% yields.…”