β-Fluoroamphetamines via the Stereoselective Synthesis of Benzylic Fluorides
摘要:
A range of substituted aryl epoxides undergo efficient ring-opening hydrofluorination upon treatment with 0.33 equiv of BF3 center dot OEt2 in CH2Cl2 at -20 degrees C to give the corresponding syn-fluorohydrins, consistent with a mechanism involving a stereoselective S(N)1-type epoxide ring-opening process. The benzylic fluoride products of these reactions are valuable templates for further elaboration, as demonstrated by the preparation of a range of aryl-substituted beta-fluoroamphetamines.
Pinacolatoboron fluoride (pinBF) is an efficient fluoride transfer agent for diastereoselective synthesis of benzylic fluorides
作者:Alexander J. Cresswell、Stephen G. Davies、Aude L.A. Figuccia、Ai M. Fletcher、Dorus Heijnen、James A. Lee、Melloney J. Morris、Alice M.R. Kennett、Paul M. Roberts、James E. Thomson
DOI:10.1016/j.tetlet.2014.12.044
日期:2015.6
The incorporation of alkoxy ligands within a range of alkoxyfluoroboranes and dialkoxyfluoroboranes results in fluoroborane reagents with attenuated Lewis acidity and increased ability to donate fluoride ion(s) when compared to boron trifluoride itself. Pinacolatoboron fluoride (pinBF), prepared in situ from BF3 center dot OEt2 and bis(O-trimethylsilyl)pinacol, has been identified as an efficient fluoride donor which allows highly stereoselective S(N)1-type epoxide ring-opening (with retention of configuration) of a range of trans-beta-methyl-substituted aryl epoxides to give the corresponding syn-fluorohydrins. The substrate scope of this transformation is more broad than the analogous protocol using boron trifluoride alone. (C) 2014 Elsevier Ltd. All rights reserved.