Difluoro-lambda3-bromane-induced oxidative carbon-carbon bond-forming reactions: ethanol as an electrophilic partner and alkynes as nucleophiles.
Reported here for the first time are the oxidative couplings of alkynes and primary alcohols yielding conjugated enones. Although the BF3-catalyzed reaction of terminal alkynes with p-trifluoromethylphenyl(difluoro)-lambda3-bromane results in the fluoro-lambda3-bromanation of triple bonds to afford (E)-beta-fluorovinyl-lambda3-bromanes, reaction of an alkyne with the difluoro-lambda3-bromane in the presence of an alcohol and BF3-Et2O affords directly conjugated enones in good yields. The reaction proceeds in a highly stereo- and regioselective manner under metal-free conditions. Interestingly, no formation of enones was detected, when difluoro-lambda3-iodane p-CF3C6H4IF2 was used instead of the lambda3-bromane. A mechanism involving a lambda3-bromane-induced oxidation of an alcohol to an aldehyde, [2 + 2] cyclization with alkynes yielding 2H-oxetes, and finally the electrocyclic ring opening is discussed.
Ochiai
Masahito
M
Graduate School of Pharmaceutical Sciences, University of Tokushima, 1-78 Shomachi, Tokushima 770-8505, Japan. mochiai@ph.tokushima-u.ac.jp
Yoshimura
Akira
A
Mori
Takeshi
T
Nishi
Yoshio
Y
Hirobe
Masaya
M
D000480:Alkynes / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D006842:Hydrocarbons, Brominated / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
D000480:Alkynes; D006842:Hydrocarbons, Brominated; C528824:p-trifluoromethylphenyl(difluoro)-lambda3-bromane; D000431:Ethanol; D002244:Carbon