title: Synthesis and resolution of the biaryl-like diphosphine (S)-Me2-CATPHOS, preparation of a derived rhodium precatalyst and applications in asymmetric hydrogenation.
abstract: This protocol describes the synthesis of a representative example of the enantiopure biaryl-like CATPHOS class of diphosphines, (S)-9,9'-dimethyl-9,9',10,10'-tetrahydro-9,10,9',10'-biethenobianthracene-11,11'-bis(diphenylphosphino)-12,12'-diyl ((S)-Me(2)-CATPHOS), and its derived cationic rhodium-based hydrogenation precatalyst. The C(2)-symmetric framework of Me(2)-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 Me(2)-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 derived rhodium complex forms a highly effective catalyst for the asymmetric hydrogenation of a range of dehydroamino acid derivatives, as well as (E)-β-aryl-(enamido)phosphonates, giving ee values in excess of 99%, the highest to be reported for the latter class of substrate. The total time required for the synthesis of (S)-Me(2)-CATPHOS, including resolution, reduction and crystallizations, is 130 h and preparation of the corresponding rhodium precatalyst requires an additional 24-26 h.
authors.affiliation: School of Chemistry, Newcastle University, Newcastle upon Tyne, UK. simon.doherty@ncl.ac.uk
authors.forename: Simon
authors.initials: S
authors.lastname: Doherty
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Smyth
mesh_terms: D000873:Anthracenes / Q000138:chemical synthesis* / Q000737:chemistry; D002621:Chemistry / Q000379:methods; D006865:Hydrogenation; D015394:Molecular Structure; D012238:Rhodium / Q000737:chemistry*
chemical_list: C577500:(S)-9,9'-dimethyl-9,9',10,10'-tetrahydro-9,10,9',10'-biethenobianthracene-11,11'-bis(diphenylphosphino)-12,12'-diyl; D000873:Anthracenes; D012238:Rhodium