New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions:  The Bis(diphenylphosphino) Five-membered Biheteroaryls

Abstract

The synthesis and application of three examples of a new class of chiral (C(2)) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized. They were found to be optically stable at 100 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2'-bis(diphenylphosphino)-3,3'-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed.

Carbocatalysed Oxidative CC Homocouplings of Benzo‐Fused Heterocycles

“…[21] However, under the optimised indole-indole homocoupling conditions,t he reactionw as only applicable to the coupling of electronr ich 2-(4-methoxyphenyl)-substituted benzofuran and benzothiophene with low isolated yields ( Table 2, entries 10 and 11). At this point we reasonedt hat an acid additive could boost the oxidative processesb yo AC in as imilar mannera ss toichiometrico xidative couplings with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ) benefit from the addition of an acid.…”

Asymmetric Hydrogenation of α,β‐Unsaturated Carboxylic Acids Catalyzed by Ruthenium(II) Complexes of Spirobifluorene Diphosphine (SFDP) Ligands

“…[2] In the past decades, considerable efforts have been expended in this field and the Ru diacetate complexes ligated by chiral diphosphines were found to be efficient catalysts for the asymmetric hydrogenation of a,b-unsaturated carboxylic acids. The ligands reported to be highly enantioselective in this transformation included BINAP, [3] H 8 -BINAP, [4] MeO-BIPHEP, [5] P-Phos, [6] BITIANP, [7] as well as BITIOP. [8] This asymmetric hydrogenation has also been successfully applied for the synthesis of non-steriodal anti-inflammatory drugs (NSAIDs), such as isobuprofen and naproxen [9] and other chiral materials.…”

Application of SDP Ligands for Pd‐Catalyzed Allylic Alkylation

“…Since the development of DIOP ligand by Kagan [3] and co-workers in 1971, the design of chiral phosphines has for a long period been dominated by chelating diphosphine derivatives possessing a chiral scaffold. Prominent examples are the atropisomeric C 2 -symmetric diphosphines with a biaryl scaffold (such as BINAP, [4] BIPHEMP, [5] Bitianp, [6] PPhos, [7] and Segphos [8] ), the planar chiral diphosphines based on ferrocene or paracyclophane backbones (such as Josiphos [9] and Phanephos [10] ), and the central chiral diphosphines (such as Duphos [11] and Tangphos [12] ). Although these chiral diphosphines have been widely used as ligands for many asymmetric catalytic reactions, the reaction enantioselectivites are highly substrate-dependent.…”