Suzuki–Miyaura cross-couplings of secondary allylic boronic esters
作者:Ben W. Glasspoole、Kazem Ghozati、Jonathon W. Moir、Cathleen M. Crudden
DOI:10.1039/c2cc16076e
日期:——
Palladium-catalyzed cross-coupling reactions of secondary allylic boronic esters with iodoarenes were demonstrated under the conditions previously described for the coupling of benzylic substrates. The regioselectivity of the process was largely dictated by the pattern of olefin substitution.
Double-Bond Isomerization: Highly Reactive Nickel Catalyst Applied in the Synthesis of the Pheromone (9<i>Z</i>,12<i>Z</i>)-Tetradeca-9,12-dienyl Acetate
A highly reactive nickel catalyst comprising NiCl2(dppp) or NiCl2(dppe) with zinc powder, ZnI2 and Ph2PH, was applied in the isomerization of terminal alkenes to Z-2-alkenes. The double-bond geometry of the 2-alkene can be controlled via the reaction temperature to yield the 2-Z-alkenes in excellent yields and high Z-selectivities. The formation of other constitutional isomers, such as 3-alkenes, is suppressed on the basis of the proposed mechanism via a 1,2-hydride shift from the metal to the Ph2P ligand. The nickel-catalyzed isomerization reaction was then applied in the synthesis of (9Z,12Z)-tetradeca-9,12-dienyl acetate, a pheromone with a 2Z,5Z-diene subunit.
Enantiospecific, Regioselective Cross-Coupling Reactions of Secondary Allylic Boronic Esters
作者:Laetitia Chausset-Boissarie、Kazem Ghozati、Emily LaBine、Jack L.-Y. Chen、Varinder K. Aggarwal、Cathleen M. Crudden
DOI:10.1002/chem.201303683
日期:2013.12.23
enantioselective Suzuki–Miyaura cross‐coupling of chiral, enantioenriched secondaryallylic boronic esters is described (see scheme; DME=dimethoxyethane, Bpin = pinacolboryl, dba = dibenzylideneacetone). Mechanistic studies show that the reactions proceed via γ‐selective transmetalation followed by reductive elimination. The reaction provides the first independent confirmation that the transmetalation of
phosphine–pyridine–imidazoline (PNNimid) ligand [Fe]Cl2 = (PNNimid)FeCl2}, upon activation with NaHBEt3, catalyzes the isomerization of 1,1-disubstituted alkenyl boronates to synthetically valuable but previously difficult-to-access trisubstituted (Z)-alkenyl boronates with excellent regio- and stereoselectivity. The loading of the catalyst activator relative to iron was found to affect the selectivity and