Antonio Togni

Asymmetric allylic alkylation catalyzed by palladium-sparteine complexes

Abstract The cationic complex [Pd(η 3 -C 3 H 5 )(sparteine)]PF 6 ( 6 ) was found to be a suitable catalyst precursor for the asymmetric alkylation of allylic acetates with Na[CH(COOMe) 2 ] as the nucleophile. This constitutes one of the first and still rare examples of a phosphine-free system for this type of Pd-catalyzed reaction. Using 5 mol % of 6 , alkylation products were obtained in up to 90% isolated yield and 85 % enandomeric excess. The alkylation reaction was shown to occur with overall retention of configuration, indicating an analogous mechanism to the one previously proposed for phosphine-containing catalysts. The reactivity of allylic acetates is strongly dependent upon the nature of the substituents, open-chain aliphatic substrates being unreactive.

Enantioselective synthesis of β-hydroxy-α-aminophosphonic acid precursors

The gold(I) catalyzed aldol reaction of diethyl α-isocyanomethylphosphonate with benzaldeyde gave the oxazoline 3, a β-hydroxy-α-aminophosphonic acid precursor, with high enantio- and diastereoselectivity (98 % trans, 85 % ee) by employing a chiral ferrocenylamine ligand. The use of 31P NMR spectroscopy with the chiral solvating agent (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol was found to be a powerful tool for determination of optical purity.

Enantioselective synthesis: Catalysis of the aldol reaction by neutral gold(I)-chiral ferrocenylphosphine complexes. Crystal structure of the complex [{(η5-C5H4PPh2)(η5-C5H3(PPh2)CH(Me)N(Me)CH2CH2NMe2)Fe}2(AuCl)3] · Et2O

Abstract The chiral aminoferrocenylphosphine [(η 5 -C 5 H 4 PPh 2 )(η 5 -C 5 H 3 (PPh 2 )CH(CH 3 )-N(CH 3 )CH 2 CH 2 N(CH 3 ) 2 )Fe] ( 1 ) reacts with (H 3 C) 2 SAuCl to give neutral gold(I) complexes that are active catalysts for the enantioselective coupling of isocyanoacetate esters with aldehydes, forming dihydrooxazoles. The structure of the trimeric complex [(rac- 1 ) 2 (AuCl) 3 ] · Et 2 O has been determined by X-ray diffraction.

Asymmetric synthesis: Modification of chiral ferrocenylamine ligands for the gold(I)-catalyzed aldol reaction

Abstract The synthesis of a chiral ferrocenylamine ligand, ( R )-( S )- 11 , with a modifiable ester group is described. High diastereo- and enantioselectivity were obtained in the gold(I)-catalyzed aldol reaction using ( R )-( S )- 11 as a ligand.

The gold(I)-catalyzed aldol reaction utilizing chiral ferrocenylamine ligands : synthesis of N-benzyl-substituted ligands

The synthesis and characterization of (R)-N-{2-[(R)-N-2-hydroxy-1-propyl-N-benzyl]aminoethyl}-N-benzyl-1-[(S)-1′,2-bis(diphenylphosphino)ferrocenyl]ethyl amine (9) and selected carbamate esters is described. The stereoselectivity of the gold(I)-catalyzed reaction of benzaldehyde with methyl iso-cyanoacetate was compared using the N-benzyl-substituted versus the corresponding N-methyl-substituted ferrocenylamine ligands. The lower diastereo- and enantioselectivity obtained using the N-benzyl-substituted ferrocenylamine ligands is consistent with the transition-state model proposed for the stereoselective step of the gold(I)-catalyzed aldol reaction utilizing ferrocenylamine ligands possessing both central and planar chirality.