Tailoring buchwald-type phosphines with pyrimidinium betaines as versatile aryl group surrogates
A derivatization of dialkylbiarylphosphines consisting in the formal replacement of their distal aryl group by a pyrimidinium betaine is reported. Two achiral representatives of this new class of Buchwald-type phosphines have been successfully synthesized through two strategies. The first one is based on a last stage introduction of the phosphino moiety, and the second one consists in a modular, one-pot, three-step procedure starting from an o-bromoaryl phosphine. The resulting phosphines have been coordinated onto gold(I) and palladium(II) centers and have been employed as supporting ligands in Pd-catalyzed Suzuki-Miyaura cross-coupling of aryl halide substrates.
Nol-Duchesneau, Ludovik,Lugan, Nol,Lavigne, Guy,Labande, Agns,Csar, Vincent
supporting information
p. 5085 - 5088
(2014/12/11)
Does Formal Intramolecular Transfer of an Acidic Deuterium to a Site of Halogen-Lithium Exchange Show That Lithium-Halogen Exchange Is Faster than Loss of the Acidic Deuterium? Evidence in Favor of an Alternative Mechanism
Reactions in which there is formal intramolecular transfer of an acidic deuterium to a site of halogen-lithium exchange could be interpreted to show that initial halogen-lithium exchange occurs faster than loss of the acidic deuterium.However studies of the competition between halogen-metal-deuterium exchange and deuterium loss for N-deuterio-N-alkyl-o, -m, and -p-halobenzimides are not consistent with that mechanism.We suggest an alternative in which initial loss of the acidic deuterium is followed by halogen-lithium exchange to give a dilithiated intermediate.Deuterium transfer to the site of halogen-lithium exchange then occurs by reaction of the dilithiated species intermolecularly with unreacted N-deuteriated amide.The halogen-lithium exchange is faster than complete mixing of the reactants and can occur either in an initially formed deprotonated complex or in a transient high local concentration of organolithium reagent.Evidence for both possibilities is provided.Two reactions from the literature in which halogen-lithium exchange appears to be faster than transfer of an acidic hydrogen have been reinvestigated and found to be interpretable in terms of similar sequences.
Beak, Peter,Musick, Timothy J.,Chen, Chin-wen
p. 3538 - 3542
(2007/10/02)
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