Joseph P. A. Harrity

Ru complexes bearing bidentate carbenes: from innocent curiosity to uniquely effective catalysts for olefin metathesis

The discovery and development of a new class of Ru-based catalysts for olefin metathesis is described. These catalysts, particularly those that do not bear a phosphine ligand, have been demonstrated to promote unique levels of reactivity in a variety of olefin metathesis reactions. The design and development of supported and chiral optically pure variants of this class of Ru catalysts for use in enantioselective metathesis are discussed as well. All catalysts are air stable, reusable, and can be employed with unpurified solvents.

Investigation of the Scope and Regiochemistry of Alkynylboronate Cycloadditions with Sydnones

The cycloaddition of alkynylboronates and sydnones provides a convenient and highly regioselective method for the synthesis of a broad range of di-, tri-, and tetrasubstituted pyrazole boronic esters. The origins of an observed regiochemical divergence in the reactions of terminal alkynylboronates with their more substituted analogues have been studied by DFT methods.

Spirocycle assembly through selective tandem ring closing metathesis reactions

Abstract A range of functionalised spirocyclic systems have been prepared under mild and neutral conditions by tandem selective ring closing olefin metathesis reactions. Additionally, a marked preference for 5-membered ring closure over 7-membered ring closure was observed which appears to be a result of a kinetically favoured cyclisation process.

Synthesis of Ynone Trifluoroborates toward Functionalized Pyrazoles

The synthesis of a range of novel ynone trifluoroborates has been achieved, in a two-pot process from propargylic alcohols. These alkynes have been subsequently used in the formation of a range of pyrazole trifluoroborate salts via cyclization with hydrazines. The products are generated with high levels of regiocontrol and in excellent yields and represent versatile synthetic intermediates.

A Nickel‐Catalyzed Benzannulation Approach to Aromatic Boronic Esters

Benzannulation reactions are one of the most efficient and direct methods for assembling highly substituted aromatic compounds. Nonetheless, this strategy provides a number of considerable challenges that relate to chemoselectivity and regioselectivity. With regard to exploiting such reactions for the production of synthetically useful organic compounds, aromatic boronic acids represent an important target as they are widely acknowledged as being amongst the most useful and versatile intermediates in synthetic chemistry. Indeed, such compounds have been accessed by benzannulation techniques involving transition metal catalysis and pericyclic processes. Our preliminary work in this area showed that the D tz benzannulation reaction could be exploited to access quinone boronic esters in good yield and with excellent levels of regiocontrol. As quinone boronic acids can serve as precursors to bioactive quinones, and have recently emerged as useful substrates for regioand stereocontrolled Diels–Alder reactions, this technique held some significant synthetic potential. However, drawbacks associated with the requirement for a stoichiometric organochromium reagent in the D tz benzannulation reaction prompted us to search for a transition metal catalyzed approach. As outlined in Scheme 1, the Cr-mediated benzannulation reaction can be envisaged to be a Cr-templated ketene electrocyclization. We considered a metal-templated vinylketene [4+2] cycloaddition to be an alternative strategy to oxygenated aromatic boronic ester systems. Indeed, such processes are known and exploit readily available cyclobutenones as the vinylketene precursors. Specifically, Liebeskind et al. have carried out detailed studies into metalmediated vinylketene formation and reactivity. Moreover, the same group showed that Ni catalysis can mediate the reaction of cyclobutenones with alkynes to provide phenols. In addition, Kondo, Mitsudo et al. have employed Rh and Ru catalysts to promote the cycloaddition of cyclobutenones with strained alkenes. Danheiser has employed a tandem [2+2] cycloaddition–electrocyclic ring closure as a transition metalfree approach to highly substituted phenols. Given that alkynylboronates are known to undergo transmetalation reactions with group 7 and 8 transition metal complexes, we began our studies by investigating the potential for chemoselective cycloaddition of these substrates using Rh and Ni catalysts. As outlined in Scheme 2, while the Rh-

Alkyne [3 + 2] Cycloadditions of Iodosydnones Toward Functionalized 1,3,5-Trisubstituted Pyrazoles

The cycloaddition of 4-iodosydnones with terminal alkynes proceeds with excellent regiocontrol to provide 5-iodo pyrazoles. These products participate smoothly in subsequent C-C and C-heteroatom bond forming processes.

Promotion of the chromium carbene Dötz annulation reaction under sonochemical and dry state adsorption conditions

Abstract The chromium carbene Dotz annulation reaction proceeds very rapidly in the presence of ultrasound giving good yields of quinone product on oxidative workup. Moreover, the yield of annulated product has been improved by adsorbing the reagents onto silica and heating at moderate temperatures. Both these modifications have proved to be successful for a variety of complexes and alkynes.

Ambient-Temperature Cobalt-Catalyzed Cycloaddition Strategies to Aromatic Boronic Esters

The room-temperature cobalt-catalyzed [4 + 2] cycloaddition of alkynylboronates and 1,3-dienes provides a convenient and general method for the synthesis of benzene-based aromatic boronic esters. Two complementary aromatization strategies involving in situ elimination and DDQ oxidation were explored, with the latter finding more generality. Finally, the potential of this technique to generate highly functionalized biaryls has been demonstrated via the synthesis of chiral (racemic) DMAP catalysts.

A divergent strategy to the withasomnines

A concise synthesis of three members of the withasomnine family of natural products is reported. The synthesis features a regioselective sydnone-alkynylboronate cycloaddition followed by Suzuki cross coupling and silyl group removal, and marks the first divergent approach to this family of pyrazole based natural products.

A novel approach to functionalised pyridazinone arrays

A series of 3,6-dichloro-1H-pyridazin-4-ones have been prepared via the cycloaddition of 3,6-dichlorotetrazine with alkynylboronates, and their employment as useful synthetic intermediates was highlighted through a selection of highly regioselective C-O, C-S and C-C bond forming reactions.