An official website of the United States government
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
Aminoboration of simple alkenes with nitrogen nucleophiles remains an unsolved problem in synthetic chemistry; this transformation can be catalyzed by palladium via aminopalladation followed by transmetalation with a diboron reagent. However, this catalytic process faces inherent challenges with instability of the alkylpalladium(II) intermediate toward β-hydride elimination. Herein, we report a palladium/iron cocatalyzed aminoboration, which enables this transformation. We demonstrate these conditions on a variety of alkenes and norbornenes with an array of common nitrogen nucleophiles. In the developed strategy, the iron cocatalyst is crucial to achieving the desired reactivity by serving as a halophilic Lewis acid to release the transmetalation-active cationic alkylpalladium intermediate. Furthermore, it serves as a redox shuttle in the regeneration of the Pd(II) catalyst by reactivation of nanoparticulate palladium.more » « less
-
Herein we report the palladium-catalyzed borylation of aryl halides (iodides or bromides) under base-free conditions utilizing a commercially available Lewis acidic mediator, Zn(OTf)2. Under these conditions, an array of electronically and functional group-diverse aryl iodides and bromides undergo borylation to afford the corresponding aryl boronic esters in up to 82% isolated yield. Mechanistic investigations are consistent with Zn(OTf)2 enabling transmetalation between a cationic Pd(II)-Ar intermediate and B2pin2 via halide abstraction. Furthermore, stabilization of the cationic [ArPdII]+ complex with added [BArF4]– significantly improves reaction efficiency with electron-poor arenes.more » « less
-
We report the intramolecular 1,n-aminoboration for the simultaneous synthesis of aza-heterocycles with distal carbon–boron bonds. Pd-catalyzed remote 1,n-aminoboration occurs with 1,2-disubstituted alkenes; upon aminopalladation of the olefin, chain-walking generates the terminal Pd-alkyl intermediate which selectively undergoes Fe-catalyzed borylation. Terminal bishomoallylic amines, amides, carba-mates, and ureas afford the borylated pyrrolidines and lactams through 1,2-aminoboration. Forty-one examples of 1,n-borylated hetero-cycles are presented with yields up to 92% yield. Derivatization of the products is explored: cross-coupling, amination, and oxidation to access unnatural amino alcohols and acids.more » « less
