Selective P−C(sp³) Bond Cleavage and Radical Alkynylation of α‐Phosphorus Alcohols by Photoredox Catalysis

Abstract

Herein the first P-C(sp ) bond cleavage and radical alkynylation of α-phosphorus alcohols to construct phosphonoalkynes is reported. The phosphorus radical is generated upon P-C bond cleavage reaction via the alkoxyl radical through photoredox catalysis with cyclic iodine(III) reagents. Various arylphosphinoyl-, alkylphosphinoyl-, phosphonate-, and phosphonic amide alcohols serve as radical phosphorus precursors to construct phosphonoalkynes for the first time.

Recent Synthetic Applications of the Hypervalent Iodine(III) Reagents in Visible-Light-Induced Photoredox Catalysis

“…Following the above successes, they further extended the dual CIR/photoredox catalytic methodology to α-phosphorus alcohols in 2018 (Jia et al, 2018 ) ( Figure 6C ). Various arylphosphinoyl-, alkylphosphinoyl-, phosphonate-, and phosphonic amide alcohols undergo P-C(sp 3 ) bond cleavage/radical alkynylation with EBXs to construct phosphonoalkynes for the first time.…”

“…Due to the excellent coordinating property of iodine atom, HIRs can easily experience ligand exchange reaction with organic acids to form the hypervalent iodine-coordinated carboxylates. When combination with the photoredox catalysis, those hypervalent iodine-coordinated carboxylates frequently undergo homolytic cleavage to access highly reactive hypervalent iodine radicals as well as the oxygen radicals, thus triggering the decarboxylative functionalization reactions or other transformations (Huang et al, 2016 ; Jia et al, 2018 ). Based on the above concept, Chen and co-workers have conducted a series of studies on novel dual CIR/photoredox catalytic system (Huang et al, 2015 ; Jia et al, 2016 , 2017 ), and the research results proved that CIRs played a crucial role in activating the substrates of organic acids and alcohols toward photoredox catalysis.…”

“…In contrast, hydroxyl-, alkoxyl-, and acetoxy- benziodoxoles (BI-OH, BI-OR, and BI-OAc) are usually acted as the oxidant for activation of carboxylic acids (Huang et al, 2016 ), alcohols (Liu et al, 2018 ) or alkyl C-H bonds (Li et al, 2017 ) for the generation of oxygen- or carbon-centered radicals under photoredox catalysis. In certain cases (Jia et al, 2016 , 2018 ), two HIRs were employed in the same photoredox procedure: one of which acts as a reagent and the other serves as mild oxidant.…”

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

“…In 2012, the Li group first used alkynylbenziodoxoles for decarboxylative radical alkynylation under silver salt and persulfate conditions [ 19 ]. In 2014, the Chen group discovered that alkynylbenziodoxoles (BI-alkyne) readily participated in photoredox catalysis as the radical alkynylation reagent [ 20 ], after which various applications in photoredox catalysis were reported [ 21 – 27 ].…”

“…Currently, the use of BI-alkyne for radical alkynylation is limited to unsubstituted alkynylbenziodoxoles. While effective, its reactivity with some radical precursors was compromised [ 19 – 27 ]. The Waser group pioneered the study of substituted alkynylbenziodoxoles for the electrophilic alkynylation reactivity, however, no significant improvements were observed by the derivatizations [ 28 – 32 ].…”