Thomas E. Cole

Migration of groups from zirconium to boron: Aspects of synthesis and utility

Abstract The hydrozirconation of alkenes or alkynes yields the dicyclopentadienyl alkyl- or alkenylzirconium chloride, respectively, in high yields and with high regioselectivity. The reaction of these organozirconium compounds with a boron halide results in the exchange of the halogen and organic group, forming the organoborane. We report here a systematic investigation of the transmetallation of organic groups from zirconium to a variety of boron compounds. The migration is facile to a variety of boron halides, yielding structurally different types of alkyl or alkenylboranes in good to high yields. Exploiting the unique reactivity and selectivity of the hydrozirconation reaction for the preparation of organoboranes expands the range of potential of both metals for synthesis.

Transmetalation of organic groups from zirconacycles to haloboranes: A new route to borolane compounds

Abstract The reaction of styrene and “Cp 2 Zr” forms the trans-2,5-diphenylzirconacycle. Transmetalation of this zirconacyle with an equivalent of boron trichloride forms the 1-chloro-trans-2,5-diphenylborolane with retention of stereochemistry. This B-chloroborolane is converted into other boranes and can be oxidized to the diol.

Simple conversion of anhydrides of boronic and borinic acids to the corresponding organodihaloboranes and diorganohaloboranes

Abstract The reaction of the anhydrides of boronic or borinic acids with trihaloboranes in hydrocarbon solvents leads to the clean exchange of the oxygen and halide to form the organodihaloboranes and diorganohaloboranes in good to excellent yields.

A Simple and Convenient Method for Synthesizing Trialkoxyboranes and Trialkoxyboroxins Using Calcium Hydride as a Drying Agent

Abstract Trialkoxyboranes are conveniently synthesized in good to excellent yields from the corresponding alcohols or phenols and boric acid using calcium hydride as a drying agent. This method is successful for a variety of sterically hindered alcohols. In a new general route, trialkoxyboroxins are formed under mild reaction conditions from these same readily available materials. The trialkoxyboranes and trialkoxyboroxins can be interconverted by addition of stoichiometric amounts of boric acid or the alcohols/phenols, in the presence of calcium hydride. Calcium hydride is most effective for the removal of water. This allows for a simple and convenient route for the preparation of the useful trialkoxyboranes and the previously inaccessible trialkoxyboroxins, for further investigation or applications.

Migration of alkyl groups from zirconium to various haloboranes

Abstract The hydrozirconations of acyclic alkenes are known to yield the dicyclopentadienyl-1-aklyl-zirconium chlorides regioselectively and in high yields. These alkyl groups may readily be transmetallated to the haloboranes forming regioisomeric pure alkylboranes in good yields. In principle, this migration reaction combines the facile hydrozirconation and unique isomerization reactions of organozirconiums with the established chemistry of boron, expanding the utility of both metals for use in organic synthesis.