Esters as Radical Acceptors: β‐NHC‐Borylalkenyl Radicals Induce Lactonization by C−C Bond Formation/Cleavage on Esters. Issue 19 (4th April 2019)

• Record Type: Journal Article
• Authors: Shimoi, Masaki; Maeda, Katsuhiro; Geib, Steven J.; Curran, Dennis P.; Taniguchi, Tsuyoshi
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 19(2019)
• Page Start: 6357
• Page End: 6361
• Publication Date: 2019-04-04
• Subjects: alkynes -- boranes -- lactones -- radical reactions -- synthetic methods; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201902001
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: 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. Abstract : Radical behavior : Radical lactonization of substituted propargyl acetates with N‐heterocyclic carbene boranes has been developed. The reaction proceeds by cyclization of a β‐borylalkenyl radical with an ester with subsequent elimination of a methyl group.