6482-26-4Relevant articles and documents
Second Generation Total Synthesis of (–)-Preussochromone D
Beller, Marc Paul,Kerste, Eric,Koert, Ulrich
, (2020/07/02)
An improved enantioselective synthesis of the natural product (–)-preussochromone D (3) and first insights into a possible route to the trans-preussochromones E and F are described. Starting from commercially available 5-hydroxy-4H-chromen-4-one, two ster
In situ derivatization/solid-phase microextraction for the determination of haloacetic acids in water
Sarrion,Santos,Galceran
, p. 4865 - 4873 (2007/10/03)
An in situ derivatization solid-phase microextraction method has been developed for the determination of haloacetic acids (HAAs) in water. The analytical procedure involves derivatization of HAAs to their methyl esters with dimethyl sulfate, headspace sampling using solid-phase microextraction (SPME), and gas chromatography-ion trap mass spectrometry (GC/ITMS) determination. Parameters affecting both derivatization efficiency and headspace SPME procedure, such as the selection of the SPME coating, derivatization-extraction time and temperature, and ionic strength, were optimized. The commercially available Carboxen-poly(dimethylsiloxane) (CAR-PDMS) fiber appears to be the most suitable for the determination of HAAs. Moreover, the formation of HAA methyl esters was dramatically improved (up to 90-fold) by the addition of tetrabutylammonium hydrogen sulfate (4.7 μmol) to the sample as ion-pairing agent in the derivatization step. The precision of the in situ derivatization/HS-SPME/GC/ITMS method evaluated using an internal standard gave relative standard deviations (RSDs) between 6.3 and 11.4%. The method was linear over 2 orders of magnitude, and detection limits were compound-dependent, but ranged from 10 to 450 ng/L. The method was compared with the EPA method 552.2 for the analysis of HAAs in various water samples, and good agreement was obtained. Consequently, in situ derivatization/HS-SPME/GC/ITMS is proposed for the analysis of HAAs in water.
Vinylic Substitution of 1,2-Dibromo-1,2-difluoroethylene and Tribromofluoroethylene. An Intramolecular kBr/kF Element Effect and Apparent Inversion of Configuration in SNV Reactions
Shainyan, Bagrat A.,Rappoport, Zvi
, p. 3421 - 3428 (2007/10/02)
The reactions of (E/Z)-1,2-dibromo-1,2-difluoroethylene(1) and of tribromofluoroethylene (2) with alkoxide ions and of 1 with p-toluenethiolate ion give multiplicity of products.The reaction of 1 with 1 equiv of NaOMe gives mainly a 2:1 mixture of the product of one bromine displacement, together with methyl dimethoxyacetate (3), methyl bromofluoroacetate (4), 1,1,2-trifluoro-2-bromoethyl ether (7), and 1,1-difluoro-1,2,2-trimethoxyethane (8).With 2 equiv of MeO(1-) 3 and 4 are the main products, and at 130 deg C, dimethyl ether 5 is also formed.With EtOCH2CH2O(1-) 1 gave 2-ethoxyethyl bromofluoroacetate (9), bis(2-ethoxyethyl) ether (10), and E/Z mixtures of the substitution products EtOCH2CH2OC(F)=C(F)Br (12) and EtOCH2CH2OC(Br)=C(F)Br (13).Reaction of 2 with excess RO(1-) (R = Me, Et) gives alkyl dibromoacetates, while with 1 equiv of RO(1-) only a bromine from the =C(F)Br carbon is displaced.Reaction of 1 with p-TolSNa in MeOH gives the reduction-substitution product p-TolSC(F)=CHF (18), together with (P-TolS)2 (16) and p-TolSMe (17).The same reaction in DMSO gives E/Z mixtures of the product of displacement of one bromine (19) or two bromines (20).Formation of the products is rationalized by an initial nucleophilic attack on the vinylic carbon followed by leaving group expulsion, giving, e.g., 12, 13, 19, or 20.Hydrolysis of the intermediate or addition of HF to the initial substition product gives saturated products, e.g., 3, 4, 7, or 8, while SN2 reactions on the ether oxygen give ethers 5 and 10.A bromophilic reaction gives the reduction-substitution product 18, while hydrolysis-decarboxylation leads to 17.The regiospecificity of the nucleophilic addition is due to polar and hyperconjugative effects.An intramolecular element effect kBr/kF of > 10 is reported for the first time in the reaction of 1 with EtOCH2CH2O(1-).This value and the absence of such effects in other reactions are consistent with a much higher nucleofugality from a (1-)CC(F)Br system of Br(1-) compared with F(1-).The E/Z compositions of 18-20 indicates an apparent inversion in their formation, but it is not known whether these compositions are thermodynamically or kinetically controlled.
