Chelation-Controlled Diastereoselective Reduction of α-Fluoroketones
摘要:
The effect of Ti-based Lewis acids on the reduction of alpha-fluoropropiophenone was examined to determine whether chelation control could be used to direct the diastereoselectivity of conversion to an alpha-fluoro alcohol. Pretreatment of alpha-fluoropropiophenone with TiCl4 followed by reduction with LiBH4 in diethyl ether or methylene chloride provided the syn diastereomer predominantly, while use of Ti(OiPr)4 under identical conditions provided the anti diastereomer as the major product. The products are consistent with a chelation-controlled mechanistic pathway in the former reduction and a nonchelation pathway in the latter case. Detailed 1H, 13C, and 19F NMR studies were consistent with chelation between TiCl4 and alpha-fluoropropiophenone under the reaction conditions utilized in this study. Reduction of other alpha-fluoroketones in the presence of TiCl4 also provided a high degree of diastereoselectivity in the conversion to alpha-fluoro alcohols, showing the generality of this approach.
Open-Shell Fluorination of Alkyl Bromides: Unexpected Selectivity in a Silyl Radical-Mediated Chain Process
作者:Gabrielle H. Lovett、Shuming Chen、Xiao-Song Xue、K. N. Houk、David W. C. MacMillan
DOI:10.1021/jacs.9b11434
日期:2019.12.26
We disclose a novel radical strategy for the fluorination of alkyl bromides via the merger of silyl radical-mediated halogen-atom abstraction and benzophenone photosensitization. Selectivity for halogenatomabstraction from alkyl bromides is observed in the presence of an electrophilic fluorinating reagent containing a weak N-F bond despite the predicted favorability for Si-F bond formation. To account
Enantioselective Synthesis of Vicinal Halohydrins via Dynamic Kinetic Resolution
作者:Abel Ros、Antonio Magriz、Hansjörg Dietrich、Rosario Fernández、Eleuterio Alvarez、José M. Lassaletta
DOI:10.1021/ol052821k
日期:2006.1.1
[reaction: see text] Expanding the scope of enantioselective catalysis via DKR, transfer hydrogenation of a variety of cyclic alpha-halo ketones was accomplished using the Noyori/Ikariya (R,R)- or (S,S)-I catalysts and either HCO(2)H/Et(3)N or HCO(2)Na/n-Bu(4)NBr in H(2)O/CH(2)Cl(2) as the hydrogen sources. Good yields of vicinal bromo-, chloro-, and fluorohydrins with excellent de and ee levels were