| Abstract
| - Chemo- and diastereoselectivities of homo- and cross-coupling reactions of Co2(CO)6-complexedpropargyl radicals were studied. The alternative radical generation methodsreduction of respective cationswith Zn or Cp2Co and one-step mediation with THF or Tf2Owere employed. In the case of cobaltcomplexes with terminal triple bonds, the product distribution is nearly statistical and dependent uponthe reducing agent with the concentration of the cross-coupling product 8 falling in the range 38−49%.The diastereoselectivity varied widely (de 40−92%) with the preponderant formation of d,l-diastereoisomers 7−9 in both homo- and cross-coupling reactions. The highest level of stereocontrol was achievedin THF- and Tf2O-mediated reactions (de up to 92%), while the reductions with Cp2Co were inferior inboth homo- and cross-coupling processes (de 40−56%). An introduction of a γ-aromatic ring revealeda kinetic differentiation at the radical generation step that, in turn, resulted in a nonstatistical distributionof homo- and cross-dimers. The d,l-diastereoselectivity is found to be systematically lower for homo-dimer 16, containing a γ-phenyl substituent at the triple bond (de: 16 14−64%; 7 52−84%). The observedchemoselectivities are accounted for on the basis of the computed values of charge distribution in therequisite cations.
- Chemo- and diastereoselectivities of homo- and cross-coupling reactions of topologically diverse Co2(CO)6-complexed propargyl radicals were studied. The structural and electronic parameters were used, as effective tools, to control the product distribution (the ratio of symmetrical and unsymmetrical radical dimers) and to provide for an excellent d,l-diastereoselectivity (up to 96%).
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