Rhodium-catalyzed double [2 + 2 + 2] cycloaddition of 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne with tethered diynes: a modular, highly versatile single-pot synthesis of NU-BIPHEP biaryl diphosphines.
ABSTRACT Rhodium-catalyzed double [2 + 2 + 2] cycloaddition of 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne with tethered diynes provides a straightforward, single-pot procedure for the synthesis of a new class of tropos biaryl diphosphine, NU-BIPHEP. This methodology represents a significant improvement on existing multistep procedures. Enantiopure Lewis acid platinum complexes of these diphosphines are highly efficient catalysts for carbonyl-ene and Diels-Alder reactions, and ruthenium diphosphine-diamine complexes catalyze the asymmetric reduction of ketones to give ee's that rival those obtained with their BINAP counterpart.
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ABSTRACT: This protocol describes the synthesis of a representative example of the electron-rich biaryl-like KITPHOS class of monophosphine, 11-dicyclohexylphosphino-12-phenyl-9,10-dihydro-9,10-ethenoanthracene (H-KITPHOS). The bicyclic architecture of H-KITPHOS is constructed via [4+2] Diels-Alder cycloaddition between 1-(dicyclohexylphosphinoylethynyl)benzene and anthracene. H-KITPHOS monophosphine is prepared via an operationally straightforward three-step procedure and is isolated in an overall yield of ∼55%. The synthesis of palladium and gold precatalysts of H-KITPHOS are also described; the yields of analytically pure complexes are high (75-85% and 85-90%, respectively). The palladium complex of H-KITPHOS forms a highly active catalyst for C-C and C-N cross-coupling of a range of aryl and heteroaryl chlorides and bromides, and the electrophilic Lewis acid gold complex efficiently catalyzes a host of cycloisomerizations. The total time required for the synthesis of H-KITPHOS is 95 h; the preparation of corresponding palladium and gold precatalysts requires an additional 7-8 h, and, if necessary, crystallizations will require a further 48 h.Nature Protocol 10/2012; 7(10):1870-83. · 8.36 Impact Factor
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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.Nature Protocol 10/2012; 7(10):1884-96. · 8.36 Impact Factor
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ABSTRACT: All enantiopure atropisomeric (atropos) ligands essentially require enantiomeric resolution or synthetic transformation from a chiral pool. In sharp contrast, the use of tropos (chirally flexible) ligands, which are highly modular, versatile, and easy to synthesize without enantiomeric resolution, has recently been the topic of much interest in asymmetric catalysis. Racemic catalysts bearing tropos ligands can be applied to asymmetric catalysis through enantiomeric discrimination by the addition of a chiral source, which preferentially transforms one catalyst enantiomer into a highly activated catalyst enantiomer. Additionally, racemic catalysts bearing tropos ligands can also be utilized as atropos enantiopure catalysts obtained via the control of chirality by a chiral source followed by the memory of chirality. In this feature article, our results on the asymmetric catalysis via the combination of various central metals and tropos ligands are summarized.Chemical Communications 10/2012; 48(90):11050-69. · 6.38 Impact Factor