![]() © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. This account describes the novel synthetic methods developed in our laboratory, in the perspective of closely related work by others, for the synthesis of phosphonyl/sulfonylpyrazoles, pyrazole esters and the total synthesis of Withasomnine, a natural product, by using 1,3-dipolar cycloaddition as the key step. ![]() ![]() Over the last few years, our group has been engaged in the synthesis of phosphonyl/sulfonylpyrazoles and pyrazole esters by employing Bestmann-Ohira Reagent (BOR) and its sulfur and ester analogs as 1,3-dipole precursors with various dipolarophiles. Synthesis of Functionalized Pyrazoles via 1,3-Dipolar Cycloaddition of α-Diazo-β-ketophosphonates, Sufones and Esters with Electron-Deficient Alkenes.ġ,3-Dipolar cycloaddition of diazo compounds with olefinic substrates is a promising atom-economic strategy for the construction of functionalized pyrazoles. This new methodology was further applied in a highly efficient synthesis of JAK 1/2 inhibitor (R)-ruxolitinib. The reaction tolerates a large variety of functional groups and labelling experiments gave insights into the reaction mechanism. The rhodium-catalyzed asymmetric N-selective coupling of pyrazole derivatives with terminal allenes gives access to enantioenriched secondary and tertiary allylic pyrazoles, which can be employed for the synthesis of medicinally important targets. Haydl, Alexander M Xu, Kun Breit, Bernhard Regio- and enantioselective synthesis of N-substituted pyrazoles by rhodium-catalyzed asymmetric addition to allenes.
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