Can a Butadiene-Based Architecture Compete with its Biaryl Counterpart in Asymmetric Catalysis? Enantiopure Me-CATPHOS, a Remarkably Efficient Ligand for Asymmetric Hydrogenation

Abstract

The double Diels-Alder cycloaddition between 9-methylanthracene and 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne affords the oxide of the atropos diphosphine, Me-CATPHOS, which has an unusual bicyclic buta-1,3-diene-based architecture. Quantum chemical methods using DTF reveal that the barrier to atropinterconversion in Me-CATPHOS is 130 kJ mol -1 , while the corresponding barrier for its unsubstituted counterpart is only 23 kJ mol -1 , entirely consistent with the former being an atropos diphosphine while the latter belongs to the tropos class of ligand. rac-Me-CATPHOS can be resolved by fractional crystallization of the diastereoisomeric complexes formed with (2R,3R)-(-)-2,3-O-dibenzoyltartaric acid and reduction of the resulting enantiopure oxide, accomplished by silane reduction in xylene at 130 °C, to afford an operationally straightforward, three-step synthesis of an entirely new class of atropos buta-1,3-diene-based diphosphine. Rhodium complexes of enantiopure Me-CATPHOS catalyze the asymmetric hydrogenation of a range of dehydroamino acid derivatives, in some cases giving ee's in excess of 99% and in all cases showing a significant enhancement compared with its BINAP counterpart. Gratifyingly, Rh/(S)-Me-CATPHOS outperforms all existing catalysts for the asymmetric hydrogenation of (E)-β-dehydroamino phosphonates, many of which are based on markedly more expensive biaryl-and ferrocenyl-based diphosphines. Surprisingly, in the case of the dehydroamino acid substrates, (S)-Me-CATPHOS provides product of opposite absolute stereochemistry to that obtained with (S)-BINAP, despite both ligands having an S ax configuration, whereas (S)-Me-CATPHOS exerts (S)-BINAP-like stereoinduction for the hydrogenation of β-enamidophosphonates; both ligands afford product with the same absolute configuration.

Synthesis and resolution of the biaryl-like diphosphine (S)-Me2-CATPHOS, preparation of a derived rhodium precatalyst and applications in asymmetric hydrogenation

“…Gratifyingly, in addition to being an architectural analog of biaryl diphosphines, our preliminary studies revealed Me 2 -CATPHOS to be a highly efficient ligand for the rhodium-catalyzed asymmetric hydrogenation of a range of dehydroamino acid derivatives, as well as (E)-β-aryl-(enamido)phosphonates, in some cases giving ee values in excess of 99%, and in all cases showing a significant enhancement compared with 1; in fact, the ee values obtained for the latter substrates are the highest to be reported 47,48 . Lewis acid platinum-group metal complexes of (S)-Me 2 -CATPHOS also catalyze the carbonyl-ene reaction, and although catalyst performance is substrate-and metal-specific ee values that matched those achieved with 1 were obtained for selected substrates 49 .…”

“…2), which is structurally similar to the biaryl diphosphines in that two diphenylphosphino groups are connected by an unsaturated tether, albeit not a biaryl fragment but an anthracene-derived bicyclic buta-1,3-diene-based framework 46,47 . Key features of Me 2 -CATPHOS (The prefix in the CATPHOS nomenclature/acronym is used to specify the substituents on bridgehead carbon atoms attached to C2 and C3 of the buta-1,3-diene tether.)…”

“…We have previously reported details of the synthesis of CATPHOS (R = H) 46 and (S)-Me 2 -CATPHOS 47 . In this contribution, we describe a specific protocol for the synthesis of (S)-9,9′-dimethyl-9,9′,10,10′-tetrahydro-9,10,9′,10′-biethenobianthracene-11,11′-bis(diphenylphosphino)-12,12′-diyl (6) starting from commercially available substrates; a protocol for the synthesis of the corresponding cationic rhodium precatalyst ((S)-7) is also described (Fig.…”

Alkenylphosphines: Applications in Synthesis, Catalysis and Coordination Chemistry

“…Enantiopure Catphos 105b, obtained after fractional crystallization using a tartaric acid derivative, was recently used as ligand in the Rh-catalyzed hydrogenation reactions [64]. With [Rh(COD) 2 ][BF 4 ] (1 mol%) and 105b (1.1 mol%), excellent results were obtained with methyl-2-acetamidoacrylate (98% yield and >99% ee).…”

Spannungsvermittelte Bildung chiraler, optisch aktiver Buta‐1,3‐diene

“…[8,9] Zusamenfassend haben wir die spannungsvermittelte [19] chiralen molekulare Magneten, [20] chiralen Speichereinheiten [21] oder als neuartige atropisomere Dien-Liganden für die asymmetrische Katalyse. [22] Eingegangen am …”