Visible Light Induced Brønsted Acid Assisted Pd‐Catalyzed Alkyl Heck Reaction of Diazo Compounds and N‐Tosylhydrazones

Abstract

A mild visible light-induced palladium-catalyzed alkyl Heck reaction of diazo compounds and N-tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acidassisted generation of hybrid palladium C(sp 3 )-centered radical intermediate, which allowed for new selective C À H functionalization protocol.Scheme 1. The reactivity of diazo compounds with alkenes.

Visible-Light-Promoted Aerobic Oxyphosphorylation of α-Diazoesters with H-Phosphine Oxides

“…Over the past few decades, visible-light-promoted reaction has been identified a sustainable and powerful strategy for organic synthesis . In this context, great achievements have been made in the visible-light-promoted conversion of diazo compounds, including X–H (X = C, O, S, N, or Si) insertion reactions . In sharp contrast to the formation of metal carbene intermediates in the transition metal-catalyzed reactions of diazo compounds, their visible-light-promoted reactions commonly proceed via free carbene intermediates generated by light-induced denitrogenation.…”

Photocatalytic C(sp3) radical generationviaC–H, C–C, and C–X bond cleavage

“…142 The Rc generation could also proceed with complete C]N cleavage of diazo compounds, which has been explored by many laboratories. [143][144][145][146] In 2016, the group of Megger merged the Ruphotoredox catalysis with a chiral Rh(I) catalysis for asymmetric a-C(sp 3 )-H functionalisation of arylacetyl imidazoles with diazoacetate as the Rc source (Scheme 34). 147 In the early stage, the Rh(I) chelated the carbonyl and imidazolyl groups of the substrate and formed an enolate complex (Rh-enolate).…”

Light-Driven Palladium-Radical Hybrid Species: Mechanistic Aspects and Recent Examples

“…The formation of radicals from diazo compounds usually leads to the generation of cyclopropanes due to the carbene-like reactivity of such species when reacting with alkenes, 56 which makes the use of diazo compounds for the generation of free radical intermediates scarce in the literature. 57 Regarding the generation of hybrid Pd I -radical species, a groundbreaking contribution by Gevorgyan and coworkers 58 exemplified the possible generation of such intermediates through the formation of Pd carbenes followed by a hydride shift and light-induced homolysis of the Pd-C bond. An alternative path was also proposed via protoncoupled electron transfer (PCET) between the diazo compound, or even direct SET via a diazonium ion.…”