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DOI: 10.1055/s-2008-1078639
Rh-Catalyzed Enantioselective Addition of Arylboronic Acids to Aliphatic Imines
Contributor(s):Mark Lautens, Valentina AureggiUniversity of California, Berkeley, USA
Enantioselective Synthesis of α-Aryl Alkylamines by Rh-Catalyzed Addition Reactions of Arylboronic Acids to Aliphatic Imines
Angew. Chem. Int. Ed. 2008, 47: 5623-5626
Publication History
Publication Date:
22 August 2008 (online)
Key words
aliphatic imines - arylboronic acids - rhodium
Significance
The enantioselective catalytic addition of arylboronic acids to aliphatic imines is reported. The corresponding α-aryl alkylamines are obtained with excellent yields and enantioselectivities. This work represents one of the few examples of boronic acid addition to aliphatic imines.
Comment
The catalytic enantioselective addition of boronic acids with
aromatic imines was previously reported (D. J. Weix, Y. Shi, J.
A. Ellman
J. Am. Chem. Soc. 2005, 127, 1092).
The catalyst is preformed by stirring the pre-catalyst and the ligand
in dioxane for 90 min at 70 ˚C. An excess of ligand to
rhodium ratio is required to improve the enantioselectivity. The
imines are activated with a diphenylphosphinoyl (dpp) or tosyl substituent
on the nitrogen. Under the optimized conditions
α-
and β-branched N-tosyl imines
are converted into the corresponding products with excellent enantioselectivities
and high yields (up to 96% ee, 71-89% yield). N-dpp-Imines are also versatile substrates;
however, α-branched N-dpp-imines show
a slightly reduced yield (75-79%) with high enantioselectivity
(84-95% ee). Both electron-rich and -poor arylboronic
acids are suitable for this transformation.