Annulative Aminosulfonylation of Unactivated Alkenes for Accessing Pyrazolines via Multicomponent SO₂ Insertion

Abstract

A direct arylsulfonylation of β,γ-unsaturated hydrazones method, in which sulfonated pyrazolines are accessed by a three-component reaction of β,γ-unsaturated hydrazones, DABSO, and aryldiazonium tetrafluoroborates, has been developed without external oxidants or catalysts. This transformation is triggered by the formation of arylsulfonyl radicals in situ from the reaction of aryldiazonium tetrafluoroborates and DABSO, and is enabled by controllable generation of C center radical, in which DABSO was utilized as the sulfone source and an oxidant in this radicalmediated cascaded reaction. A wide range of substrates can be applied in this process to afford pyrazolines in good yield, and it is amenable for gram-scale synthesis.

Alkylsulfonylation of alkenes involving copper carbene coupling: access to alkyl–alkyl sulfones

“…On the basis of the above results and previous related reports, 10–12,14 a plausible mechanism for this alkyl radical-initiated alkylsulfonylation reaction is presented (Scheme 3). Firstly, substrate 1a is transformed into carbon radical A in the presence of Cu( i ) species via a single electron transfer process, followed by intramolecular cyclization to generate intermediate B .…”

“…In recent years, the incorporation of an “SO 2 ” group derived from sulfur dioxide surrogates (such as DABSO and inorganic sulfites) into organic molecules while simultaneously forming two C–S bonds has become a holy grail in the synthesis of sulfone compounds. 7–12 Among them, the carbon radical (C-radical)-initiated sulfonylation reaction of alkenes 10–12 has attracted significant interest from chemists due to its highly efficient step and oxidative economies. Typically, there are two strategies to achieve this transformation as depicted in Scheme 1b: strategy I: the C-radicals selectively capture sulfur dioxide to generate sulfonyl radicals, which subsequently engage in an addition reaction with alkenes, resulting in the formation of carbon-centered radicals, and subsequent functionalization of these radicals leads to the desired products; strategy II: the C-radicals first undergo an addition reaction with the carbon–carbon double bond leading to carbon-centered radicals, followed by the capture of sulfur dioxide to generate sulfonyl radicals, which are then functionalized to obtain sulfone compounds.…”

“…Typically, there are two strategies to achieve this transformation as depicted in Scheme 1b: strategy I: the C-radicals selectively capture sulfur dioxide to generate sulfonyl radicals, which subsequently engage in an addition reaction with alkenes, resulting in the formation of carbon-centered radicals, and subsequent functionalization of these radicals leads to the desired products; strategy II: the C-radicals first undergo an addition reaction with the carbon–carbon double bond leading to carbon-centered radicals, followed by the capture of sulfur dioxide to generate sulfonyl radicals, which are then functionalized to obtain sulfone compounds. Although significant progress has been made in this field, the current methods 10,11 for synthesizing sulfone compounds through the radical sulfonation reaction of alkenes mainly rely on strategy I. In contrast, there is a notable lack of methods 12 to construct these crucial compounds using strategy II.…”