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Esters as Radical Acceptors: β‐NHC‐Borylalkenyl Radicals Induce Lactonization by C−C Bond Formation/Cleavage on Esters
Author(s) -
Shimoi Masaki,
Maeda Katsuhiro,
Geib Steven J.,
Curran Dennis P.,
Taniguchi Tsuyoshi
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201902001
Subject(s) - chemistry , radical , medicinal chemistry , carbene , hydrogen atom abstraction , alkoxy group , propargyl , bond cleavage , photochemistry , borane , alkene , organic chemistry , catalysis , alkyl
Substituted propargyl acetates are converted into 4‐boryl‐2(5 H )‐furanones upon thermolysis in the presence of an N‐heterocyclic carbene borane (NHC‐borane) and di‐ tert ‐butyl peroxide. The acetyl methyl group is lost during the reaction as methane. Evidence suggests that the reaction proceeds by a sequence of radical events including: 1) addition of an NHC‐boryl radical to the triple bond; 2) cyclization of the resultant β‐borylalkenyl radical to the ester carbonyl group; 3) β‐scission of the so‐formed alkoxy radical to provide the 4‐boryl‐2(5 H )‐furanone and a methyl radical; and 4) hydrogen abstraction from the NHC‐borane to return the initial NHC‐boryl radical and methane.