Radical Germylzincation of α‑Heteroatom-Substituted Alkynes
journal contributionposted on 29.11.2018, 00:00 by Karen de la Vega-Hernández, Elise Romain, Anais Coffinet, Kajetan Bijouard, Geoffrey Gontard, Fabrice Chemla, Franck Ferreira, Olivier Jackowski, Alejandro Perez-Luna
The regio- and stereoselective addition of germanium and zinc across the C–C triple bond of nitrogen-, sulfur-, oxygen-, and phosphorus-substituted terminal and internal alkynes is achieved by reaction with a combination of R3GeH and Et2Zn. Diagnostic experiments support a radical-chain mechanism and the β-zincated vinylgermanes that show exceptional stability are characterized by NMR spectroscopy and X-ray crystallography. The unique feature of this new radical germylzincation reaction is that the C(sp2)–Zn bond formed remains available for subsequent in situ Cu(I)- or Pd(0)-mediated C–C or C–heteroatom bond formation with retention of the double bond geometry. These protocols offer modular access to elaborated tri- and tetrasubstituted vinylgermanes decorated with heteroatom substituents β to germanium that are useful for the preparation of stereodefined alkenes.
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germaniumgermylzincation reactionbond geometryheteroatom substituents βprotocols offerstereodefined alkenesR 3 GeHβ- zincated vinylgermanestetrasubstituted vinylgermanesX-ray crystallographyphosphorus-substituted terminalradical-chain mechanismNMR spectroscopyDiagnostic experiments supportstereoselective additionRadical GermylzincationEt 2 Zn