Bismuth-mediated arylation

Initial efforts were focused on the development of a catalytic protocol for the arylation of hydroxyarenes using Ar3BiX2 reagents. The individual steps oxidation, arylation and transmetallation were investigated separately to be combined in the final step. While the arylation of phenolic substrates results in low overall yields and selectivities, switching to 2- naphthol improved yields drastically, allowing for a mechanistic investigation into the rate and selectivity determining step of the oxidative arylation, the role of electronic properties of substrate and transferred aryl group, as well as the counter ion on the bismuth centre. The diaryl bismuth reaction product was identified and conditions for transmetallation from organoboron reagents to result in a Ar3Bi compound were developed. While oxidation of the Bi(III) reagent could be achieved efficiently with a variety of oxidising agents, a combination of the three steps proved unsuccessful due to the inherent incompatibility of the necessary reagents, precluding development of a catalytic application of bismuth. For a stepwise stoichiometric approach, a variety of bismacylic compounds have been prepared and tested concluding in a thiabismine dioxide core. Different bismacycle (pseudo)- halide salts of the thiabismine dioxide core have been prepared and their capability for transmetallation have been investigated. The reaction proceeds via a μ-oxo intermediate under basic conditions using readily available boronic acids. With a scope involving electron rich to electron poor aryl motifs as well as sterically demanding and even heterocyclic rings, a simple and robust transmetallation protocol has been developed. The subsequent oxidation and arylation was achieved using mCPBA as the oxidant with 2-naphthol as the initial substrate. Notably, no base is required in the arylation process. The scope was extended to numerous naphtholic and phenolic substrates. Mechanistic investigations of all significant processes have been conducted allowing for unprecedented insight into bismuth-mediated arylation, that provide a deeper understanding and provides a priori prediction for untested substrate combinations

Modular bismacycles for the selective C–H arylation of phenols and naphthols

Given the important role played by 2-hydroxybiaryls in organic, medicinal and materials chemistry, concise methods for the synthesis of this common motif are extremely valuable. In seeking to extend the synthetic chemists’ lexicon in this regard, we have developed an expedient and general strategy for the ortho-arylation of phenols and naphthols using readily-available boronic acids. Our methodology relies on in situ generation of a uniquely reactive Bi(V) arylating agent from a bench stable Bi(III) precursor via telescoped B-to-Bi transmetallation and oxidation. By exploiting reactivity 2 that is orthogonal to conventional metal-catalyzed manifolds, diverse aryl and heteroaryl partners can be rapidly coupled to phenols and naphthols under mild conditions. Following arylation, highyielding recovery of the Bi(III) precursor allows for its efficient re-use in subsequent reactions. Mechanistic interrogation of each key step of the methodology informs its practical application and provides fundamental insight into the under-exploited reactivity of organobismuth compounds

Bismuth-mediated arylation

Initial efforts were focused on the development of a catalytic protocol for the arylation of hydroxyarenes using Ar3BiX2 reagents. The individual steps oxidation, arylation and transmetallation were investigated separately to be combined in the final step. While the arylation of phenolic substrates results in low overall yields and selectivities, switching to 2- naphthol improved yields drastically, allowing for a mechanistic investigation into the rate and selectivity determining step of the oxidative arylation, the role of electronic properties of substrate and transferred aryl group, as well as the counter ion on the bismuth centre. The diaryl bismuth reaction product was identified and conditions for transmetallation from organoboron reagents to result in a Ar3Bi compound were developed. While oxidation of the Bi(III) reagent could be achieved efficiently with a variety of oxidising agents, a combination of the three steps proved unsuccessful due to the inherent incompatibility of the necessary reagents, precluding development of a catalytic application of bismuth. For a stepwise stoichiometric approach, a variety of bismacylic compounds have been prepared and tested concluding in a thiabismine dioxide core. Different bismacycle (pseudo)- halide salts of the thiabismine dioxide core have been prepared and their capability for transmetallation have been investigated. The reaction proceeds via a μ-oxo intermediate under basic conditions using readily available boronic acids. With a scope involving electron rich to electron poor aryl motifs as well as sterically demanding and even heterocyclic rings, a simple and robust transmetallation protocol has been developed. The subsequent oxidation and arylation was achieved using mCPBA as the oxidant with 2-naphthol as the initial substrate. Notably, no base is required in the arylation process. The scope was extended to numerous naphtholic and phenolic substrates. Mechanistic investigations of all significant processes have been conducted allowing for unprecedented insight into bismuth-mediated arylation, that provide a deeper understanding and provides a priori prediction for untested substrate combinations

Polyurethanes and polyallophanates via sequence-selective copolymerization of epoxides and isocyanates

Aryl isocyanates are introduced as comonomers for ring-opening copolymerization (ROCOP) with epoxides. Informed by studies of reaction kinetics, we show that divergent sequence selectivity for AB- and ABB-type copolymers can be achieved with a single dimagnesium catalyst. The resulting materials respectively constitute a new class of polyurethanes (PUs) and a new class of materials featuring an unprecedented backbone structure, the polyallophanates (PAs). The successful use of isocyanate comonomers in this way marks a new direction for the field of ROCOP while providing distinct opportunities for expansion of PU structural diversity. Specifically, the methodology reported herein delivers PUs featuring fully substituted (tertiary) carbamyl nitrogen atoms, a structural motif that is almost inaccessible via extant polymerization strategies. Thus, in one step from commercially available comonomers, our methodology expands the scope of ROCOP and gives access to diverse materials featuring both privileged (PU) and unexplored (PA) microstructures.Aryl isocyanates are introduced as comonomers for ring-opening copolymerization (ROCOP) with epoxides. Informed by studies of reaction kinetics, we show that divergent sequence selectivity for AB- and ABB-type copolymers can be achieved with a single dimagnesium catalyst. The resulting materials respectively constitute a new class of polyurethanes (PUs) and a new class of materials featuring an unprecedented backbone structure, the polyallophanates (PAs). The successful use of isocyanate comonomers in this way marks a new direction for the field of ROCOP while providing distinct opportunities for expansion of PU structural diversity. Specifically, the methodology reported herein delivers PUs featuring fully substituted (tertiary) carbamyl nitrogen atoms, a structural motif that is almost inaccessible via extant polymerization strategies. Thus, in one step from commercially available comonomers, our methodology expands the scope of ROCOP and gives access to diverse materials featuring both privileged (PU) and unexplored (PA) microstructures