Journal
ORGANIC PROCESS RESEARCH & DEVELOPMENT
Volume 23, Issue 8, Pages 1638-1645Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.oprd.9b00257
Keywords
off-cycle; catalysis; carboranes; cage-walking; deboronation
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Funding
- NIGMS [R35GM124746]
- National Defense Science and Engineering Graduate Fellowship (NDSEG)
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Off-cycle processes in a catalytic reaction can dramatically influence the outcome of the chemical transformation and affect its yield, selectivity, rate, and product distribution. While the generation of off-cycle intermediates can complicate reaction coordinate analyses or hamper catalytic efficiency, the generation of such species may also open new routes to unique chemical products. We recently reported the Pd-mediated functionalization of carboranes with a range of O-, N-, and C-based nucleophiles. By utilizing a Pd-based catalytic system supported by a biarylphosphine ligand developed by Buchwald and co-workers, we discovered an off-cycle isomerization process (cage-walking) that generates four regioisomeric products from a single halogenated boron cluster isomer. Here we describe how several off-cycle processes affect the regioisomer yield and distribution during Pd-catalyzed tandem cage-walking/cross-coupling. In particular, tuning the transmetalation step in the catalytic cycle allowed us to incorporate the cage-walking process into Pd-catalyzed cross-coupling of sterically unencumbered substrates, including cyanide. This work demonstrates the feasibility of using tandem cage-walking/cross-coupling as a unique low-temperature method for producing regioisomers of monosubstituted carboranes.
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