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1.
A series of α-mono- and α,α-difluoro-β-ketophosphonates were synthesized in moderate to good yields with excellent selectivities via electrophilic fluorination by Selectfluor. Subsequently, synthetic potential of the obtained α-monofluoro-β-ketophosphonates was demonstrated by their application in synthesis of α-monofluoro-β-aminophosphonates, useful building blocks in the preparation of phosphapeptides.  相似文献   

2.
α-Chloro-1,2-diones and α-fluoro-1,2-diones were prepared from the corresponding α-chloroaldimines by a sequence of reactions involving cyanation to α-cyanoenamines, α-halogenation to form α-chloro- or α-fluoroimidoyl cyanides and addition of organolithium reagents across the nitrile moiety, followed by acidic hydrolysis. All steps are straightforward and occur without side reactions finally leading to regiospecifically chlorinated and fluorinated 1,2-diones in good yields.  相似文献   

3.
CF3CFBr2 was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF3CFBr2 under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested.  相似文献   

4.
Enantioselective α-sulfenylation of α-fluoro-β-ketoesters 4 with phenylsulfenyl chloride catalyzed by DBFOX-Ph/Ni(II) complex afforded the corresponding α-fluoro-α-sulfenyl-β-ketoesters 2 in moderate to good yields with excellent enantiomeric excesses up to 93% ee. α-Fluoro-α-sulfenyl-β-ketoesters can be effectively converted to tri-fluorinated α-sulfenylcarboxylates by the use of DAST, which should be useful intermediates for the synthesis of non-racemized fluorinated isosteres of pharmaceutically attractive SM32. The enantioselective α-phenylsulfenylation as well as α-pentafluoro-phenylsulfenylation of non-fluorinated β-ketoesters 5 were also carried out under the same catalyst conditions affording up to 95% ee of the products 6-8.  相似文献   

5.
The ring opening fluorination of glycidic gem-cyanoesters was achieved by action of pyridine polyhydrofluoride at 25°C in dichloromethane. The regioselective nucleophilic substitution reaction allows the synthesis of a new class of fluorohydrins with OH, CN and CO2R on the same carbon atom.  相似文献   

6.
The chemoselective and diastereoselective synthesis of syn-α-bromo-α-fluoro-β-lactams was achieved using the diethylzinc-mediated Reformatsky-type reaction of ethyl dibromofluoroacetate with imines. The reaction led to diastereomerically pure β-lactams in good to moderate yields (up to 78% yield) with only small amounts of aziridine derivatives. Noncyclized 3-amino-2-bromo-2-fluoro carboxylic esters, usual Reformatsky adducts, were not formed. In contrast, reactions carried out under typical Reformatsky conditions using zinc metal were poorly chemoselective, leading to mixtures of β-lactams and aziridine derivatives.  相似文献   

7.
8.
The catalytic enantioselective electrophilic α-hydrazination promoted by chiral nickel complexes is described. Treatment of α-fluoro-β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino α-fluoro-β-ketoesters with high yields (80-96%) and enantioselectivities (up to 78% ee).  相似文献   

9.
The catalytic enantioselective conjugate addition reaction of α-fluoro-β-ketoesters to nitroalkenes promoted by chiral bifunctional organocatalysts is described. The treatment of α-fluoro-β-ketoesters with nitroalkenes under mild reaction conditions afforded the corresponding Michael adducts containing a fluorinated quaternary stereogenic center with excellent enantioselectivity (up to >99% ee).  相似文献   

10.
《Tetrahedron: Asymmetry》2000,11(10):2195-2204
This report describes the synthesis of enantiomerically pure (2R,3R)-, (2R,3S)-, (2S,3S)- and (2S,3R)-2-amino-3-hydroxy-2-methyl-3-phenylpropanoic acids, four quaternary α-amino acids, using a stereodivergent synthetic route and starting from (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinals. The key step involves the asymmetric Grignard additions to the above chiral aldehydes, in which high levels of asymmetric induction are observed.  相似文献   

11.
Primary amines catalyzed the asymmetric Michael addition of ethyl 2-fluoro-2-nitroacetate to enones to provide chiral α-fluoro-α-nitro ester ketones with two contiguous stereogenic centers, one of which is a fluorinated quaternary chiral center, with excellent enantioselectivities and in moderate to good yields.  相似文献   

12.
13.
The first enantioselective Reformatsky-type reaction of ethyl iodofluoroacetate has been accomplished with alkyl aryl ketones. High diastereoselectivities and excellent enantioselectivities for the major diastereomer (93-95% ee) were achieved with large alkyl groups. For smaller alkyl groups the diastereoselectivities were moderate, but excellent enantioselectivities were obtained for both diastereomers (79-94% ee).  相似文献   

14.
The Strecker reaction was performed via a one-pot three component condensation of hetero aromatic/aromatic aldehydes, secondary amines and trimetylsilyl cyanide in the presence of propylphosphonic anhydride(T3P~) to accomplish the corresponding a-aminonitriles. The main advantages of this method are very short reaction time and excellent yields.  相似文献   

15.
The synthesis of α-amino-β-keto-esters (β-oxo dipeptides) was studied. Corresponding α-amino-β-ketoesters were prepared from BOC-(L)-Valine and BOC-(L)-isoleucine by coupling with (D,L)-threonine hydrochloride and oxidation with Dess-Martin periodinane (DMP) with a total yield of 48% and 38%, respectively. __________ Translated from Chemistry Online, 2007, 70(10): 793–796 [译自: 化学通报]  相似文献   

16.
Baylis-Hillman alcohols are excellent sources of the allylic halides ArCHCH(CH2X)(CO2R) (X=Br, Cl; R1=Me, Et, But). The Z double bond isomers are attained in high isomeric purity (>14:1, Z/E). The halides are chemo- and regiospecifically transformed into the acrylates (ArCHR2)C(CH2)(CO2R1) on treatment with Zn(R2)2 (R2=Me, Et, CH2TMS, CH2SiMe2OMe) or PrZnBr in the presence of catalytic amounts of copper(I) salts (0.5-20 mol%) in high yield.  相似文献   

17.
A synthetic strategy towards the novel amino acid β-fluoro-β-proline, a fluorinated analogue of β-proline, is elaborated. The synthesis commences from commercially available methyl 2-fluoroacrylate and involves three steps. The overall yield of β-fluoro-β-proline is 57%.  相似文献   

18.
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20.
A highly diastereoselective cross-coupling reaction of an α-bromo-α-fluoro-β-lactam with a wide range of aryl Grignard reagents was catalyzed by Ni/bis(oxazoline) in yields of up to 98%. The product was obtained diastereoselectively as an anti-isomer. This is the first successful α-arylation of an α-fluoro-β-lactam to produce diverse α-aryl-α-fluoro-β-lactams.  相似文献   

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