microwave (MW) assisted fluorination of 1-arylethanones to their corresponding 1-aryl-2-fluoroethanones has been developed. The first step utilises Selectfluor™ as a fluorinating agent in methanol forming 1-aryl-2-fluoroethanones and their corresponding dimethyl acetals. In the second step, water is added and Selectfluor™ acts as a Lewis acid in the hydrolytic cleavage of the dimethyl acetals. Compared to
para-Substituted alpha-fluoroacetophenones have been synthesised by three different routes. Electrophilic fluorination of trimethylsilyl enol ethers of acetophenones using Selectfluor (F-TEDA-BF4, 1-chloromethyl-4-fluoro- 1,4-diazoniabicyclo[ 2.2.2]octane bis-(tetrafluoroborate)) gave high to moderate yield depending on the electronic properties of the substituents. F-TEDA-BF4 mediated fluorination of acetophenones in methanol resulted in a mixture of alpha-fluoroacetophenones and the corresponding 2-fluoro- 1,1 -dimethyl acetals. The dimethyl acetals were hydrolysed using trifluoroacetic acid in water to maximise the yield of the product. Nucleophilic fluorination of alpha-bromoacetophenones using tetrabutylammoniurn hydrogen bifluoride (TBABF) led to moderate yield when having electron-donating substituents, whereas low yields were experienced when more electron-withdrawing substituents were introduced. (c) 2008 Elsevier Ltd. All rights reserved.
Gold-Catalyzed Synthesis of α-Fluoro Acetals and α-Fluoro Ketones from Alkynes
作者:Teresa de Haro、Cristina Nevado
DOI:10.1002/adsc.201000559
日期:2010.11.2
A new method to synthesize α-fluoroacetals and α-fluoroketones is presented here. In the presence of alcohols and Selectfluor, catalytic amounts of gold selectively transformed alkynes into the corresponding fluorinated acetals or ketones depending on the reaction conditions. This protocol has been applied to both terminal and internal alkynes showing a high degree of chemo- and regioselectivity