- Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes
-
Reductive elimination (RE) is a critical step in many catalytic processes. The reductive elimination of unsaturated groups (aryl, vinyl and ethynyl) from Pd(II) species is considerably faster than RE of saturated alkyl groups. Pd(II) dimethyl complexes ligated by chelating diimine ligands are stable toward RE unless subjected to a thermal or redox stimulus. Herein, we report the spontaneous RE of ethane from (azpy)PdMe2 complexes and the unique role of the redox-active azopyridine (azpy) ligands in facilitating this reaction. The (azpy)PdMe2 complexes are air- and moisture-stable in the solid form, but they readily produce ethane upon dissolution in polar solvents at temperatures from 10 °C to room temperature without the need for an external oxidant or elevated temperatures. Experimental and computational studies indicate that a bimolecular methyl transfer precedes the reductive elimination step, where both steps are facilitated by the redox-active azopyridine ligand.
- Rudenko, Andrey E.,Clayman, Naomi E.,Walker, Katherine L.,Maclaren, Jana K.,Zimmerman, Paul M.,Waymouth, Robert M.
-
-
Read Online
- Allylation reactions of aldehydes with allylboronates in aqueous media: Unique reactivity and selectivity that are only observed in the presence of water
-
Zn(OH)2-catalyzed allylation reactions of aldehydes with allylboronates in aqueous media have been developed. In contrast to conventional allylboration reactions of aldehydes in organic solvents, the α-addition products were obtained exclusively. A catalytic cycle in which the allylzinc species was generated through a B-to-Zn exchange process is proposed and kinetic studies were performed. The key intermediate, an allylzinc species, was detected by HRMS (ESI) analysis and by online continuous MS (ESI) analysis. This analysis revealed that, in aqueous media, the allylzinc species competitively reacted with the aldehydes and water. An investigation of the reactivity and selectivity of the allylzinc species by using several typical allylboronates (6a, 6b, 6c, 6d) clarified several important roles of water in this allylation reaction. The allylation reactions of aldehydes with allylboronic acid 2,2-dimethyl-1,3-propanediol esters proceeded smoothly in the presence of catalytic amounts of Zn(OH)2 and achiral ligand 4d in aqueous media to afford the corresponding syn-adducts in high yields with high diastereoselectivities. In all cases, the α-addition products were obtained and a wide substrate scope was tolerated. Furthermore, this reaction was applied to asymmetric catalysis by using chiral ligand 9. Based on the X-ray structure of the Zn-9 complex, several nonsymmetrical chiral ligands were also found to be effective. This reaction was further applied to catalytic asymmetric alkylallylation, chloroallylation, and alkoxyallylation processes and the synthetic utility of these reactions has been demonstrated. Still waters run deep: The Zn(OH)2-catalyzed allylation of aldehydes with allylboronates in aqueous media exclusively afford the α-addition products. This reaction was also applied to alkylallylation, chloroallylation, and alkoxyallylation reactions. The role of water is discussed. Copyright
- Kobayashi, Shu,Endo, Toshimitsu,Yoshino, Takumi,Schneider, Uwe,Ueno, Masaharu
-
supporting information
p. 2033 - 2045
(2013/09/23)
-
- 3-INDAZOLYL-4-PYRIDYLISOTHIAZOLES
-
The present invention provides 3-indazoyl-4-pyridylisothiazoles or a pharmaceutically acceptable salt thereof, pharmaceutical compositions thereof, and methods of using the same, as well as processes for preparing the same, and intermediates thereof.
- -
-
Page/Page column 9
(2009/10/18)
-
- Highly efficient and economic synthesis of new substituted amino-bispyridyl derivatives via copper and palladium catalysis
-
A convenient route for the synthesis of a variety of amino-bispyridyl compounds is introduced. Bispyridylamines were prepared in three steps from commercially available 2,6-dibromopyridine, via a copper mediated alkylation followed by two consecutive N-arylation reactions catalyzed by copper and palladium, respectively.
- Gaillard, Sylvain,Elmkaddem, Mohammed Kamal,Fischmeister, Cédric,Thomas, Christophe M.,Renaud, Jean-Luc
-
p. 3471 - 3474
(2008/09/21)
-