[1+1+1] Cyclotrimerization for the Synthesis of Cyclopropanes
作者:Srimanta Manna、Andrey P. Antonchick
DOI:10.1002/anie.201600807
日期:2016.4.18
The synthesis of small rings by functionalization of C(sp(3) )-H bonds remains a great challenge. We report for the first time a copper-catalyzed [1+1+1] cyclotrimerization of acetophenone derivatives under mild reaction conditions. The reaction has a broad scope for the stereoselective synthesis of cyclopropanes by trimerization of acetophenone. The developed transformation is based on an extraordinary
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.