Photochemical halogen-bonding assisted carbothiophosphorylation reactions of alkenyl and 1,3-dienyl bromides

Abstract

The photochemical halogen-bonding assisted alkenylation and dienylation of phosphoro(di)thioate diesters under batch and continuous flow is disclosed. Mechanistic studies support the formation of the halogen-bonding complex and the radical pathway.

Synthesis of Vinyl and 1,3‐Dienyl Sulfones Enabled by Photochemical Excitation of Halogen‐Bonding Complexes

“…Additionally, a high quantum yield but yet below the unit (φ = 0.9) was determined for the transformation (see the SI for a detailed description), which could point at radical chain propagation events, but we believe may be mainly attributed to the high efficiency of these processes. [28] Considering both of these experiments and also taking into account our previous experience in similar photochemical HaB assisted alkenylation reactions, [10] we believe that radical chain propagation events are unlikely to take place in this reaction. At the same time, the importance of light for the reaction to proceed was validated.…”

“…In light of all these mechanistic studies, and also based on our previous experience in photochemical halogen-bonding assisted alkenylation reactions, [10] we propose the mechanism depicted in scheme 5 for the cross-coupling reaction between alkenyl or dienyl bromides and sodium sulfinates 2. First, the formation of a HaB complex 6 between 1 (or 4) and 2 is hypothesized, which would be photoexcited with blue light, causing its fragmentation through reduction of the CÀ Br bond in an intermolecular photoinduced electron transfer (PET) event.…”

“…Our research group is pioneer in the development of catalyst-free alkenylation and dienylation reactions enabled by photochemical excitation of halogen-bonding complexes. [10] The visible-light-driven activation of these complexes has attracted considerable notice in recent times due to its role in generating carboncentered radicals, [11] thereby enabling the occurrence of unique photochemical radical-based organic transformations. [12] The halogen bond, categorized as a type of weak interaction within σ-hole interactions, [13] is characterized by a partial n!σ* charge-transfer.…”

Halogen-Bonding-Enabled Photoinduced Atom Transfer Radical Addition/Cyclization Reaction Leading to Tricyclic Heterocycles

“…Against this backdrop, research has focused on radical generation methods based on halogen bonding, which is a noncovalent interaction. , Halogen bonding involves electrostatic interactions between a positively charged region known as the sigma hole on a halogen atom and a Lewis base . Conventionally, mechanisms similar to those of a Lewis acid are commonly used to harness this interaction. , However, recent studies have revealed that upon irradiating complexes formed through halogen bonding with appropriate light, photoinduced electron transfer occurs within organic molecules, leading to the generation of various corresponding carbon radical species, including alkyl, aryl, and alkenyl radicals (Scheme d).…”