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This protocol describes the synthesis of a representative example of the enantiopure biaryl-like CATPHOS class of diphosphine, (S)-9,9′-dimethyl-9,9′,10,10′-tetrahydro-9,10,9′,10′-biethenobianthracene-11,11′-bis(diphenylphosphino)-12,12′-diyl ((S)-Me2-CATPHOS) and its derived cationic rhodium-based hydrogenation precatalyst. The C2-symmetric framework of Me2-CATPHOS is the result of a regioselective Diels-Alder cycloaddition between 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne and 9-methylanthracene, such that the bulky methyl-substituted bridgehead carbon atoms are attached to C2 and C3 of the 1,3-butadiene tether. Enantiopure Me2-CATPHOS is obtained in an operationally straightforward three-step procedure and isolated in ~50-60% overall yield and >99% enantiopurity, after diastereoselective resolution with (2R,3R)-(–)-2,3-O-dibenzoyltartaric acid. The complex forms a highly effective catalyst for the asymmetric hydrogenation of a range of dehydroamino acid derivatives as well as (E)-b-aryl-(enamido)phosphonates, giving ee’s in excess of 99%, the highest to be reported for the latter class of substrate. The total time required for the synthesis of (S)-Me2-CATPHOS, including resolution and reduction is 105-110 h and preparation of the corresponding rhodium precatalyst requires an additional 24-26 h.
Author(s): Doherty S, Smyth C
Publication type: Article
Publication status: Published
Journal: Nature Protocols
Print publication date: 20/09/2012
ISSN (print): 1754-2189
ISSN (electronic): 1750-2799
Publisher: Nature Publishing Group
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