Authors: Guillaume Pisella
Source: Infoscience (Ecole Polytechnique Fédérale de Lausanne) (article, 2021-01-01)
Field: Chemistry — Organic Chemistry

New Vinylation and Alkynylation Strategies with Hypervalent Iodine Reagents and Diazo Compounds The development of a sequential copper-catalyzed oxy-alkynylation/intramolecular [4+2] cycloaddition of allenes and arenes was investigated at first. This one-pot protocol allowed the construction of complex polycylic architectures with high efficiency from aryldiazo esters and ethynylbenziodoxolone reagents (EBX). The mild reaction conditions (23 to 90 Â°C) for the dearomatization step was unusual compared to previous literature reports and DFT computations showed that substituents on the aryl ring resulted in favorable dispersive interactions, decreasing the activation energy barrier of the cycloaddition. The bicyclo[2.2.2]octadiene products were successfully applied as ligands for rhodium. The prepared diene-rhodium complexes were extensively characterized by NMR spectroscopy and X-ray crystallography. Finally, an enantiopure ligand having a pseudo C2-symmetry was used in the conjugate addition of phenylboronic acid to cyclohexenone and furnished the Î²-functionalized ketone in good yield and with high enantioselectivity. The vinylation reactions of diazo compounds are scarce. A successful copper-catalyzed vinylation of diazo compounds with vinylbenziodoxolone reagents (VBX) as partners was reported. The transformation allowed an unprecedented gem-oxy-vinylation at the carbene center, providing functionalized Î±-vinyl-hydroxyacid derivatives in high atom and step economy. The products were obtained in excellent yields and contained synthetically versatile functional groups for post-modifications. The development of an enantioselective version of this reaction was limited and further investigations will be required to obtain high enantioselectivities. In addition, a practical synthesis of alkyl-substituted VBX reagents has been established; VBX reagents being limited to aryl substituents until then. Multicomponent reactions provide efficient means to rapidly access molecular diversity. A copper(I)-catalyzed threeâ component reaction utilizing diazo compounds, alcohols as nucleophiles and vinyl- or ethynylbenziodoxole reagents, was successfully developed. The transformation allowed the synthesis of highly functionalized allyl and propargyl ethers. The scope is broad, and extensive variations of the three partners of the reaction is possible, leading to maximal structural diversity. Extension of this work to N-nucleophiles was not as straightforward as anticipated, but good results could be obtained with anilines, trifluorodiazoethane and EBX reagents as components. Questions about the reaction mechanisms of the copper-catalyzed difunctionalizations of diazo compounds with VBX and EBX reagents have been frequent all-along this research work. Preliminary results of in-depth mechanistic investigations have been obtained. The initial assumption of an internal alkyne transfer step was first invalidated by DFT computations and was latter refuted experimentally. A complexation between the carboxylate of ethynylbenziodoxolone reagents and the copper catalyst was characterized by NMR spectroscopy and contrasted to a alkyne-copper interaction observed with ethynylbenziodoxole reagents. These two possible complexes were supported by DFT calculations. Finally, non-classical sigmoidal kinetic profiles of the oxy-alkynylation reaction were obtained by in situ 19F NMR monitoring and the Cu-EBX complex is presumably involved in the observed induction periods. Hypervalent molecule ; Diazo ; Iodine ; Alkynylation ; Chemistry ; Reagent ; Combinatorial chemistry ; Organic chemistry ; Catalysis Oxidative Organic Chemistry Reactions ; Asymmetric Synthesis and Catalysis