Organocatalysis and catalyst aggregation: a study using the asymmetric synthesis of benzofuranones as a test reaction.

A common problem encountered in enantioselective organocatalysis is the aggregation of the catalyst, which can result in a relevant decrease of the efficiency and selectivity of the process. In the asymmetric synthesis of chiral benzofuranones, recently reported by us, we noted a remarkable increase of the reaction yield upon the addition of one of the reagents in a portionwise manner rather than in a single addition. We investigated this phenomenon by several experimental techniques such as 1D and 2D NMR experiments, UV-Vis spectroscopy, circular dichroism and dynamic light scattering.

Synthesis of Benzofuranones via Malonates Desymmetrization: Yield Increase by the Portion-wise Addition of Quinones.

The organocatalyzed addition of several malonates to 1,4-benzoquinones affords benzofuranones bearing a quaternary stereocenter with good enantioselectivity. This reaction is an intramolecular desymmetrization since it proceeds through the formation of an arylated achiral malonate that cyclizes to give the reaction product. The addition rate of the quinone dramatically affects the reaction yield which was originally low.

Quinine-Catalyzed Asymmetric Synthesis of 2,2'-Binaphthol-Type Biaryls under Mild Reaction Conditions.

Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non-C2 -symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity.

Kinetic buffers.

This paper proposes a new type of molecular device that is able to act as an inverse proton sponge to slowly decrease the pH inside a reaction vessel. This makes the automatic monitoring of the concentration of pH-sensitive systems possible. The device is a composite formed of an alkyl chloride, which kinetically produces acidity, and a buffer that thermodynamically modulates the variation in pH value.