ESPHOS and SEMI-ESPHOS: A New Family of Mono- and Bidentate Diazaphospholidine Ligands for Asymmetric Catalysis

P,S-Bidentate Phosphoramidites with (Ra)-BINOL Core in Palladium-Catalyzed Asymmetric Allylic Substitution

Abstract

New P,S-bidentate phosphoramidite ligands, including these having a stereogenic phosphorus atom in the 1,3,2-dioxaphosphepine ring, have been synthesized on the basis of (Ra)-BINOL and its adamantanyl derivatives. With their participation in the Pd-catalyzed asymmetric allylic alkylation of (E)-1,3-diphenylallyl acetate with dimethyl malonate and the amination with pyrrolidine involving these ligands have afforded selectivity up to 84 and 75% ee, respectively.

Metal-catalyzed enantioselective allylation in asymmetric synthesis

Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction. The reaction may tolerate a broad range of functional groups and has been applied successfully to the synthesis of many natural products and new chiral compounds.

Alkoxy- and amidocarbonylation of functionalised aryl and heteroaryl halides catalysed by a Bedford palladacycle and dppf: a comparison with the primary Pd(ii) precursors (PhCN)2PdCl2 and Pd(OAc)2

The versatility of a Bedford-type palladacycle , namely [{Pd(micro-Cl){kappa2-P,C-P(OC6H(2)-2,4-tBu2)(OC6H(3)-2,4-tBu2)2}}2], as a primary Pd source, in combination with the ligand bis-1,1'-(diphenylphosphino)ferrocene (dppf) has been established in carbonylation reactions of aryl and heteroaryl bromides with methanol, piperidine and related nucleophiles. Palladacycle has been compared with other primary Pd sources, e.g. (PhCN)2PdCl2 and Pd(OAc)2. The efficacy of the carbonylation processes appear to be linked to the [Pd] concentration, substrate : catalyst ratio, CO pressure and reaction temperature. In amidocarbonylation, double carbonylation is observed for certain organohalides. In the case of 2,5-dibromopyridine, regioselective amination (Hartwig-Buchwald type) also occurs as a side-reaction.

Novel P,N-bidentate phosphite ligands in asymmetric catalysis

Results achieved by the authors in the synthesis of chiral P,N-phosphite ligands are summarized. Three groups of new chiral P,N-phosphites are discussed, namely, ligands derived from 1,1'-bi-2-naphthol, ligands possessing an acyclic phosphorus center, and P*-chiral ligands derived from (S)-2-anilinomethylpyrrolidine. An overview of complexation of the ligands with Rh(I) and Pd(II) precursors is given. Accessibility and stability of chiral phosphite ligands possessing acyclic phosphorus was analyzed for the first time along with their efficiency in terms of stereoselectivity. The title ligands are shown to be highly efficient in the Pd-catalyzed allylic alkylation (up to 85% ee) and, especially, allylic sulfonylation (up to 97% ee) reactions in certain cases outperformed all known catalytic systems.

Inorganic heterocyclic bis(phosphines): syntheses and structures of a 1,2-bis(diazasilaphosphetidino)ethane and its nickel, molybdenum, and rhodium complexes

Synthesis and characterization of a new, highly electron-rich, chelating bis(phosphine), based on the ethanediyl-linked inorganic heterocycle [Me(2)Si(mu-N(t)Bu)(2)P], are reported. Treatment of nickel chloride with this bis(phosphine) afforded square-planar cis-[[Me(2)Si(mu-N(t)Bu)(2)PCH(2)](2)NiCl(2)], which features isometric nickel-chloride (2.2220(8) A) and nickel-phosphorus (2.1572(8) A) bonds. The ligand reacted with cis-[(piperidine)(2)Mo(CO)(4)] to form colorless cis-[[Me(2)Si(mu-N(t)Bu)(2)PCH(2)](2)Mo(CO)(4)], which has distorted octahedral geometry and long Mo-P bonds (2.5461(18) A). Because of its potential applications in hydrogenation catalysis cis-[[Me(2)Si(mu-N(t)()Bu)(2)PCH(2)](2)Rh(COD)]BF(4) was synthesized. This square-planar, cationic rhodium(I) complex, having symmetrical Rh-P (2.250(2) A) and Rh-C (2.305(6) A) bonds, is structurally related to bis(phospholano)- and bis(phosphetano)rhodium species.

Enantioselective catalysis using phosphorus-donor ligands containing two or three P-N or P-O bonds

This review describes some recent developments in the area of asymmetric catalysis using organometallic complexes of ligands which contain two or three P-O or P-N bonds. This category of ligands has, until the last five years or so, been underrepresented in asymmetric catalysis, particularly in contrast to phosphine ligands. Recent breakthroughs in methodology for the synthesis and manipulation of such materials have resulted in the delivery of ligands which demonstrate remarkably high enantioinduction properties in a series of asymmetric transformations.

Palladium-Catalyzed Tandem Reactions To Form 1-Vinyl-1H-isochromene Derivatives1

The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the allylic system. The use of a lithium diamide base appears to be essential for success. The tert-butyldimethylsilyl protecting group is also an essential choice as it furnishes the appropriate reactivity to promote allylic substitution after the aryl coupling process. The use of more effective leaving groups, such as acetate, results in reaction of the allylic group, and no aryl coupling is observed. Through the appropriate selection of phosphine ligand and solvent, either the cyclized isochromene product or the noncyclized intermediate may be formed selectively. A short combinatorial study of the scope and limitations of the reaction, involving 24 ketones, is described.

Atropisomeric amides as chiral ligands: using (-)-sparteine-directed enantioselective silylation to control the conformation of a stereogenic axis

An enantiomerically pure (1-trimethylsilyl)ethyl group, constructed by a (-)-sparteine-directed enantioselective quench of a laterally lithiated tertiary aromatic amide, exerts powerful thermodynamic control over the conformation of the adjacent tertiary amide substituent. Ortholithiation and functionalization of the amide in the 6-position allows the single amide conformer to be trapped as an enantiomerically and diastereoisomerically pure amide atropisomer. Protodesilylation of the amide gives functionalized atropisomeric amides with a stereogenic axis of single absolute configuration, whose barriers to racemization have been determined by polarimetry. Enantiomerically pure amides bearing phosphine substituents are effective ligands in a Pd-catalyzed allylic substitution reaction-the first use of a nonbiaryl atropisomer as a chiral ligand-and give products with 90% ee. The rate of racemization of the phosphine-substituted amide is powerfully influenced by the presence of palladium.