Hydrolytic activation of C-F bonds in the gas phase by intrinsically unreactive chromium cations

Gas-phase ion chemistry in organometallic systems

This review essentially deals with positive ion/molecule reactions occurring in gas-phase organometallic systems, and encompasses a period of time of approximately 7 years, going from 1997 to early 2004. Following the example of the excellent review by Eller & Schwarz (1991; Chem Rev 91:1121-1177), in the first part, results of reaction of naked ions are presented by grouping them according to the neutral substrate, while in the second part, ligated ions are grouped according to the different ligands. Whenever possible, comparison among similar studies is attempted, and general trends of reactivities are evidenced.

Chiral amino alcohol-mediated asymmetric conjugate addition of arylalkynes to nitroolefins

[reaction: see text] The asymmetric reaction of nitroolefins with arylalkynes was mediated by dimethylzinc (or diethylzinc) and (1R,2R)-2-(dimethylamino)-1,2-diphenylethanol in toluene to provide the corresponding conjugate alkynylation products with high enantiomeric excess of up to 99% in good yields. The presence of 0.03 equiv of galvinoxyl improved the reaction yield.

A One-Pot Procedure for the Regiocontrolled Synthesis of Allyltriazoles via the Pd−Cu Bimetallic Catalyzed Three-Component Coupling Reaction of Nonactivated Terminal Alkynes, Allyl Carbonate, and Trimethylsilyl Azide

A one-pot procedure for the regiocontrolled synthesis of both 2-allyl- and 1-allyl-1,2,3-triazoles via the three-component coupling (TCC) reaction between nonactivated terminal alkynes, allyl carbonate, and trimethylsilyl azide (TMSN(3)) under a palladium and copper bimetallic catalyst has been developed. To accomplish the regioselective synthesis of the allyltriazoles, proper choice of two different catalyst systems is needed. The combination of Pd(2)(dba)(3).CHCl(3)-CuCl(PPh(3))(3)-P(OPh)(3) catalyzes the formation of 2-allyl-1,2,3-triazoles, while the combination of Pd(OAc)(2)-CuBr(2)-PPh(3) promotes the formation of 1-allyl-1,2,3-triazoles. The cooperative activity of palladium and copper catalysts plays an important role in the present transformations. Most probably, the palladium catalyst works as a catalyst for generating reactive azide species, pi-allylpalladium azide complex and allyl azide. The copper catalyst probably behaves as an activator of the C-C triple bond of the starting terminal alkynes by forming a copper-acetylide intermediate and thereby promotes the [3 + 2]-cycloaddition reaction between the reactive azide species and the copper-acetylide to form the triazole framework.

Novel iminium ion equivalents prepared through C-H oxidation for the stereocontrolled synthesis of functionalized propargylic amine derivatives

Access to stereochemically complex, polyfunctionalized amine derivatives is made possible using novel oxathiazinane N,O-acetal starting materials. These heterocycles are prepared through intramolecular sulfamate ester C-H insertion with a Rh(2+)-carboxylate catalyst and PhI(OAc)(2) as the terminal oxidant. Such compounds function as unique iminium ion equivalents to which nucleophilic alkynylzinc reagents add smoothly in the presence of BF(3).OEt(2). The coupled products are isolated in high yield (63-92%) and with good levels of diastereoinduction (6 --> 20:1). The alkyne-substituted oxathiazinanes serve as versatile building blocks and may be further manipulated through nucleophilic ring-opening reactions of the sulfamate core. The efficient construction of 1,7,8-trihydroxyindolizidine in six steps and in 34% overall yield highlights the power of these combined methods for synthesis.