Radical Germylzincation of α-Heteroatom-Substituted Alkynes

Abstract

The regio-and stereoselective addition of germanium and zinc across the CC triple bond of nitrogen-, sulfur-, oxygen-, and phosphorous-substituted terminal and internal alkynes is achieved by reaction with a combination of R 3 GeH and Et 2 Zn. Diagnostic experiments support a radical-chain mechanism and the -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(sp 2)-Zn bond formed remains available for subsequent in situ Cu(I)-or Pd(0)-mediated CC or C-heteroatom bond formation with retention of the double bond geometry. These protocols offer a modular access to elaborated tri-and tetrasubstituted vinylgermanes decorated with heteroatom substituents  to germanium that are useful for the preparation of stereodefined alkenes. Additional data and discussion, experimental details, NMR spectra for new compounds, and X-ray crystal structures (PDF) Crystallographic information files (CIF)

Ynamides in Free Radical Reactions

“…From there the authors propose another photo-catalyzed formation of a ketyl-type radical from the imine. A photocatalyzed spin-center shift (SCS) [23] would lead to the release of water and the formation of a 3-indoyl radical (31) that would then be reduced by SET (32) and protonated to yield the final product 24. The mechanism for the formation of the isoquinoline adducts 25 is similar, with an extra oxidative aromatization as the last step.…”

“…In 2018 the group of Perez‐Luna continued their investigation of the metalloid radical addition onto ynamides ( 62 ) and developed a germylzincation reaction [32] …”

“…In 2018 the group of Perez-Luna continued their investigation of the metalloid radical addition onto ynamides (62) and developed a germylzincation reaction. [32] The conditions are similar as the ones used for the silylzincationbut, instead of a silane, R 3 GeH is used, which leads to the corresponding germyl radical in the presence of diethylzinc and traces of oxygen. The resulting vinyl-zinc intermediate can then be directly trapped by an electrophiles or undergo a transmetallation with copper to provide access to a broad range of tri-or tetra-substituted alkenes 63 (Scheme 23).…”

Ligand-Controlled Regiodivergent Palladium-Catalyzed Hydrogermylation of Ynamides

“…b-Regioselectivity has been observed in hydrosilylation reactions using Lewis acid-catalyzed, Rh-catalysis, and Cu-catalysis, 26 as well as in hydrogermylation using radical germylzincation conditions (Scheme 1, a). 27 On the other hand, a-regioselectivities were obtained in the palladium-catalyzed hydrostannylation of ynamides (Scheme 1, b), except in the case of camphorsultam-derived ynamides for which a slight preference for b-regioselectivity was reported. 28e,f…”

Generation and EPR Spectroscopy of the First Silenyl Radicals, R2C=Si.−R: Experiment and Theory

“…Vinylradicals,R 2 C=CCÀR, are common intermediates widely used in organic synthesis. [1] Consequently,t hey have been studied extensively both experimentally [2] and theoretically. [3] In contrast, very little is known about the analogous Group 14 congener radicals,R 2 E = E'C À R( E, E' = C, Si, Ge), and they have only been observed in ac ryogenic matrix.…”