Bromine-Radical-Mediated Site-Selective Allylation of C(sp3)–H Bonds

Abstract

The C(sp3)–H allylation of alkanes is investigated by using allyl bromides under radical reaction conditions. In many cases, methine C–H allylation preceded methylene and methyl C–H allylation with complete or a high degree of site selectivity. The C–H allylation of allylic compounds, such as allylbenzene, gives 1,5-dienes with the SH2′ reactions of the allyl radicals occurring at the less hindered carbon.

Bromine as a Visible-Light-Mediated Polarity-Reversal Catalyst for the Functionalization of Aldehydes

“…In light of all experimental data and previous literature reports, [35][36][37][38]50 plausible mechanistic pathways for photo-mediated bromine-catalyzed PRC reactions are proposed and illustrated in Fig. 4b.…”

“…No tertiarycarbon functionalization could be detected in above transformations, even though Br radical has been reported as a suitable HAT agent for tertiary C-H bonds. 11,37 The synthetic value of this method was further demonstrated by the diversi cation of the synthesized products (Fig. 3b).…”

“…4b. Even though the homolysis of NBS to bromine radicals could be induced by blue light irradiation, 37 this process might be accelerated by heating under our optimal conditions. The generated bromine radicals can recombine to form Br 2 , which explains the requirement of constant light irradiation for the homolysis of Br 2 back to the desired Br radicals.…”

“…11,[33][34][35][36][37] In this context, Ryu et al have developed various attractive bromine-radical mediated transformations. [35][36][37] Very recently, the Miyake group described an excellent study of bromine radical catalysis promoted by energy transferring photosensitization. 38 Our group has reported photo-induced selective tertiary C(sp 3 )-H alkylation and amination using CH 2 Br 2 as a bromine radical precursor.…”

“…In stark contrast, bromine reagents have not been utilized in PRC reactions, but bromine radical (Br•) is well known as a moderately electrophilic HAT agent, which can abstract hydrogen atoms from C-H bonds to form nucleophilic carbon radicals. 11,[33][34][35][36][37] In this context, Ryu et al have developed various attractive bromine-radical mediated transformations. [35][36][37] Very recently, the Miyake group described an excellent study of bromine radical catalysis promoted by energy transferring photosensitization.…”