Hexafluoroisopropyl esters

Owing to poor volatihty, derivatization of nicotinic acid and nicotinamide are important techniques in the gc analysis of these substances. For example, a gc procedure has been reported for nicotinamide using a flame ionisation detector at detection limits of - 0.2 fig (58). The nonvolatile amide was converted to the nitrile by reaction with heptafluorobutryic anhydride (56). For a related molecule, quinolinic acid, fmol detection limits were claimed for a gc procedure using either packed or capillary columns after derivatization to its hexafluoroisopropyl ester (58). 

Also, 2-chloroethyl (RCO2CH2CH2CI), 2,2,2-trifluoroethyl (RCO2CH2CF3), 2,2,2-trichloroethyl (RCO2CH2CCI3), and hexafluoroisopropyl esters [RC02CH(CF3)2] can be synthesized for GC analysis with selective detection in a similar manner. Instead of acids, some other reagents, namely, l,l -carbonyldiimida-zole (I) and 1,3-dicyclohexylcarbodiimide (DCC, II), are recommended, as catalysts for this reaction. 

Gas Chromatography of Bile Acids as Their Hexafluoroisopropyl Ester Trifluoroacetyl Derivatives J. Chromatogr. 120(1) 181-186 (1976) CA 85 1989w... 

An important step in the development of asymmetric MBH reactions was the introduction of the quinidine-derived /Msocupreidine catalyst (/MCD) 44, by the Hatalceyama group [64, 65]. /MCD mediated the addition of acrylate 43 to a variety of aromatic and aliphatic aldehydes even at —55 °C in DMF, and afforded (R)-adducts in good yields (40-58%) and excellent enantioselectivity (ee up to 99%) (Table 5.3). The contribution of the 1,1,1,3,3,3-hexafluoroisopropyl acryl ester (HFIPA) to the reactivity of the system deserves comment. This ester displayed... 

For the synthesis of epopromycin B, precursor 47 was prepared via the addition of (S)-N-Fmoc-leucinal, 46, to HFIPA, 43, at -55 °C (Scheme 5.10) [67]. The reaction afforded, after methanolysis, two diastereoisomers the syn product 49 was obtained in 70% yield and in 99% ee, and the anti isomer 50 was obtained in 2% yield and in 99% ee. It should be noted that the hexafluoroisopropyl group was converted to the corresponding methyl ester in the alcoholysis step. The major syn isomer 49 was transformed to the epoxy end-product 51. 

The reaction of A -Fmoc-L-leudnal (139) with l,l,l>3,3>3-hexafluoroisopropyl acrylate (140) proceeded smoothly in the presence of a stoichiometric amount of cinchona alkaloid 141, even at very low temperature, to give a 6 1 mixture of j yw-ester 142 and dioxane derivative 143 (Scheme 1.62). However, the same reaction with N-Fmoc-o-leucinal (ent-139) turned out to be sluggish and only a mixture of dioxanones 143 was obtained in low yield. Thus, it can be concluded that the (/ )-selectivity of the chiral amine catalyst matches well with L-config-uration of the substrate, leading to high yn-selectivity. ... 

Another class of reaction for which chiral tertiary amines are privileged catalysts is the Morita-Baylis-Hillman type (477, 478). One of the first applications of Cinchona alkaloids to mediate an asymmetric Morita-Baylis-Hillman reaction in a natural product synthesis was reported by Hatakeyama et al. in 2001 (479). Using a stoichiometric amount of (3-isocupreidine (568), a stereoselective addition of hexafluoroisopropyl acrylate (569) to aldehyde 570 could be carried out in good yield and with excellent selectivity (99% ee) (Scheme 119). The chiral p-hydroxy ester 571 was converted further into the epoxide 572, a known intermediate in the synthesis of epopromycin B (573). Epopromycin B (573) is a plant cell wall... 

GC analysis of nonvolatile compounds such as quinolinic acid requires a derivatization step. Heyes and Markey (68) have reported quantification of quinolinic acid in rat brain, whole blood, and plasma after quinolinic acid derivatization to its hexafluoroisopropyl (HFIP) ester and GC electron capture negative ionization (Cl) MS with [ 0]quinolinic acid as an internal standard. Negative Cl efficiently forms a characteristic molecular anion and consequently negative Cl GC/... 

In addition to its biodegradability and biocompatibility, PPDX is a semicrystalline poly(ester-alt-ether) with a Tg at approximately -10 ° C and Tm at around 110 ° C. PPDX has shown to be tougher than PLAs and even HDPE with a tensile strength close to 50 MPa for an ultimate elongation ranging from 500 to 600% (Figure 17). PPDX is poorly soluble expect in exotic solvents such as hexafluoroisopropyl, 1,1,2,2-tetrachloroethane, dimethyl sulfoxide, N,N-dimethyl formaldehyde, and 1,2-dichloro ethane. ... 

Understanding of the behaviour of F-containing polymers has very recently been broadened by studies of three methacrylate polymers in which the ester group contains fluorine poly-(2-fluoroethyl methacrylate) (PFEMA), poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) and poly(hexafluoroisopropyl methacrylate) (PHFPMA). The experimental approach used is flash pyrolysis of microgram quantities of polymer at 600 °C in a helium atmosphere, followed by GC separation of volatile products and identification by MS. This produces a convenient picture of the number and relative importance of the volatile products. 

A cross-coupling of aldehydes with A-hydroxyimides, hexafluoroisopropyl alcohol, or sulfonimides (HY), catalysed by -Bu4NX (X = Br or I), has formed active intermediates RCOY that are readily converted to amides or esters in situ ... 

---