Steven W. Hansen

The stereospecific preparation of fluorinated vinyl zinc reagents from polyfluorinated vinyl iodides or bromides and zinc metal

Abstract Fluorinated vinyl zinc reagents can be prepared readily via the direct reaction of polyfluorinated vinyl iodides or bromides with zinc metal in a variety of solvents, such as DMF, DMAc, THF, glymes, and acetonitrile. The formation of symmetrical dienes via coupling of the vinyl halide is not observed. With E and Z -vinyl subtrates total retention of configuration is observed in the formation of the zinc reagents, and in subsequent functionalization reactions. The excellent thermal stability of these zinc reagents at or above room temperature, and the possibility of employing a variety of solvents allow subsequent reactions to be easily tailored to meet experimental requirements. Therefore, this approach provides a facile, easily scaled up, stereospecific, one-pot procedure to these stable vinyl organometallic reagents.

The stereospecific preparation of F-alkenyl cadmium reagents directly from F-alkenyl iodides and bromides and cadmium metal

Abstract F -Alkenyl cadmium reagents can be readily prepared via the direct reaction of F -alkenyl iodides or bromides with cadmium powder in DMF at room temperature to 60°C. The reactions proceed with total retention of configuration, and subsequent functionalization processes also proceed with stereochemical control. The thermal stability of the cadmium reagents is excellent, and the bis reagent ( Z -CF3CFCF)2Cd was isolated (via distillation) as a DMF or triglyme solvate. This approach provides a facile, easily scaled up, stereospecific, one-pot procedure to these stable alkenyl synthetic reagents.

Butatriene formation via CuBr-induced self coupling of an α-bromo vinyl zinc reagent: synthesis and X-ray structure of Z-1,1,1,6,6,6-hexafluoro-2,5-diphenylhexa-2,3,4-triene

Title cumulenes 2a and 2b were prepared by reaction of CF3(Ph)CC(Br)ZnX [X = Br, CF3(Ph)CCBr–]1 with CuBr, or by oxidative coupling of 1 with FeCl3 to form 2a,b and [CF3(Ph)CCBr–]23, which can be dehalogenated with zinc to afford 2a,b; the cumulene isomers are readily separated by silica-gel chromatography, and may be prepared in good yield on a multi-gram scale.

The hydrolysis of bromodifluoromethyltriphenylphosphonium bromide [1]

Abstract Hydrolysis of [Ph3 P + CF2Br]Br− afforded a high yield of bromodifluoromethane and triphenylphosphine oxide. Hydrolysis in the presence of a radioactive isotope of bromine or sodium iodide gave unequivocal evidence that the mechanism for this reaction proceeds through a difluorocarbene intermediate.

Preparation, stability and reactivity of fluorinated vinyl organometallic compounds

Abstract In contrast to the low stability of the fluorinated vinylic lithium or magnesium reagents, the analogous vinylic cadmium, zinc, copper, and silver reagents have been found to exhibit excellent stability. These organometallic substrates are readily prepared from the corresponding vinylic iodides or via methathesis reaction. Stereochemical integrity is preserved in all organometallic-forming reactions as well as in all subsequent chemical transformations of these reagents. In some cases (M = Cd), the bis -reagent can be isolated as a stable solid. A variety of chain-extension and/or functionalization reactions of these stable organometallic compounds will be presented and discussed.