Reductive Bromine Atom-Transfer Reaction

Abstract

Atom-transfer radical (ATR) reactions of alkenes with R-X usually give products having new C-C and C-X bonds at the adjacent carbons. However, when the reaction was carried out under irradiation using a low-pressure Hg lamp, addition/reduction products were obtained in good yield. Hydrogen bromide, formed by H-abstraction of a bromine radical from alkenes, is likely to play a key role in the reductive ATR reaction.

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

“…The bromine radical smoothly abstracts a hydrogen from the allylic C-H bond of terminal alkenes, as we recently reported. 12 We thought that the formation of allyl radicals by bromine-radical-induced C-H bond cleavage would be followed by allylation with allylic bromides at the least substituted site to give 1,5-dienes. As summarized in Scheme 4, both allylbenzene (1h) and p-allylanisole (1i) undergo the envisaged hydrogen abstraction and S H 2′ reaction at their termini to give the corresponding dienes 3ha and 3ia in acceptable yields.…”

Synthesis of Elongated Esters from Alkenes

“…A hydrogen atom was attached to the internal carbon atom and an (alkoxycarbonyl)methyl group was attached to the terminal carbon atom. A similar photoinduced transformation of alkenes has been reported, in which α‐bromo esters are used as the radical precursors . However, this procedure requires the use of a large excess of alkene (10 equiv), a quartz apparatus, a low‐pressure mercury lamp as the source of UV light, and low concentration (0.025 m ), thus significantly limiting its utility as the alkene‐based synthetic protocol.…”

Stereoselective Electro‐2‐deoxyglycosylation from Glycals

“…In all cases, excellent a-selectivity for galactal and b-selectivity for arabinal were observed, respectively. Meanwhile, it is worth mentioning that various functional groups, including ketone (23), carboxylic acid (24), uracil (25), enoate (26)(27), and 1,3-diene (28)(29) moieties are all well tolerated during the reactions. The scalability of this method was further demonstrated by an efficient synthesis of glycosylated podophyllotoxin 21 on a 934 mg scale in 75 % yield of isolated product.…”