Consecutive catalytic electrophilic fluorination/amination of β-keto esters: toward α-fluoro-α-amino acids?
摘要:
Monofluorination of beta-keto esters with Selectfluor (R) (1-chlorometliyl-4-fluoro-1,4-diazoniabicyclo[2,2,2]octane bis(tetrafluoroborate)) using CpTiCl3 as a catalyst, followed by amination with diazodicarboxylates using a Cu/Ph-Box catalyst leads to alpha-fluoro-alpha-hydrazino-beta-keto esters in good yields and good selectivities (ee up to 94%). (c) 2006 Elsevier Ltd. All rights reserved.
Titanium-Catalyzed Stereoselective Geminal Heterodihalogenation of β-Ketoesters
摘要:
beta-Ketoesters can be effectively monofluorinated with F-TEDA using CpTiCl3 as a catalyst. With the use of this catalyst, the extent of the competing difluorination does not reach 10%. [TiCl2(TADDOLato)] complexes catalyze the one-pot enantioselective heterodihalogenation of beta-ketoesters with F-TEDA and NCS to afford alpha-chloro-alpha-fluoro-beta-ketoesters in moderate to good yields. The sequence of addition of the halogenating agents determines the sense of chiral induction.