"Sandwich" Diimine-Copper Catalyzed Trifluoroethylation and Pentafluoropropylation of Unactivated C(sp3 )-H Bonds by Carbene Insertion

We report here "sandwich"-diimine copper complex-catalyzed trifluoroethylation and pentafluoropropylation of unactivated C(sp3 )-H bonds in alkyl esters, halides, and protected amines by employing CF3 CHN2 and CF3 CF2 CHN2 reagents. Reactions proceed in dichloromethane solvent at room temperature. Identical C-H functionalization conditions and stoichiometries are employed for generality and convenience. Selectivities for C-H insertions are higher for compounds possessing stronger electron-withdrawing substituents. Preliminary mechanistic studies point to a mechanism involving a pre-equilibrium forming a "sandwich"-diimine copper-CF3 CHN2 complex followed by rate-determining loss of nitrogen affording the reactive copper carbene. It reacts with trifluoromethyldiazomethane about 6.5 times faster than with 1-fluoroadamantane explaining the need for slow addition of the diazo compound.

Enantioselective gas chromatographic analysis of aqueous samples by on-line derivatisation. Application to enzymatic reactions

A new gas chromatography (GC) method is presented for analysing both the conversion and the enantiomeric excess (e.e.) of samples from alcohol dehydrogenase reactions. The chiral compounds studied were a series of saturated, straight chain alcohols, ranging from 2-butanol to 2-heptanol. The alcohols were converted to the corresponding trifluoroacetylated derivatives by injecting trifluoroacetic anhydride onto the column shortly after injection of the aqueous samples in split-injection mode (1:100) onto a Chiraldex G-TA capillary GC column. Injecting seven hundred aqueous enzymatic reaction mixtures according to the above-mentioned procedure revealed no noticeable loss of column performance. Using the new GC method, conventional sample work-up procedures such as extraction and off-line derivatisation are eliminated and throughput of samples is significantly enhanced.

Enantiomer separation of mandelates and their analogs on cyclodextrin derivative chiral stationary phases by capillary GC

Enantiomer separation of mandelates and their analogs, which are important intermediates in asymmetric synthetic and pharmaceutical chemistry, was investigated by capillary gas chromatography using different cyclodextrin derivative chiral stationary phases (CD CSPs). The used cyclodextrin derivatives included permethylated beta-CD (PMBCD), permethylated gamma-CD, heptakis(2,6-di-O-butyl-3-O-butyryl)-beta-CD, heptakis(2,6-di-O-pentyl-3-O-acetyl)-beta-CD and heptakis(2,6-di-O-nonyl-3-O-trifluoroacetyl)-beta-CD (DNTBCD), respectively. Among all the CSPs used, PMBCD and DNTBCD exhibited the broadest and best enantioselectivity for all the racemates investigated. Some thermodynamic parameters were evaluated and an enthalpy-entropy compensation effect was observed in enantiomer separation processes of mandelates and their analogs. Based on thermodynamic data and molecular mechanics calculations, the chiral recognition mechanism of mandelate derivatives on CD CSPs is discussed.