Chiral phosphonium ion tagged and spiroindane-based organocatalysts

Abstract

The research on asymmetric organocatalysis has been intensifying since the

beginning of 2000. The growing interest in this research area is driven by the

importance of the chemical synthesis of enantiomerically pure products. While

the general field of asymmetric organocatalysis has been explored intensively, the

recyclability of organocatalysts has not really been considered.

The attachment of phosphonium ion phase tags to chiral binaphthyl-based

phosphoric acid catalyst and the use of these materials in a range of

organocatalytic asymmetric Friedel-Crafts reactions of indoles have been studied.

Placement of tags at the 3 and 3’ positions of the binaphthyl core, so that they

could serve as steric blocking groups, failed to produce an active catalyst.

However, moving the phosphonium ion groups to the 6 and 6’ positions produced

an efficient and enantioselective catalyst. Aided by the presence of the phase tags,

the chiral catalyst was easily recovered at the end of the reactions, and could be

reused several times, albeit with somewhat decreased efficiency and

enantioselectivity.

Furthermore, the synthesis of 1,1’-spirobiindane-7,7’-diol and their

spiroindane-based derivatives have been explored. The (R)-1,1’-spirobiindane-

7,7’-diamine was successfully applied in exo selective asymmetric Diels-Alder

reactions of -unsaturated aldehyde with cyclopentadiene. However, moderate

results aspire further studies in assay of (R)-1,1’-spirobiindane-7,7’-diamine

derivatives, which bear various bulky groups at the 6 and 6’ positions. Moreover,

the conversion of the SPINOL into a spiroindane ketone unfortunately failed,

which was caused by the sterically crowded structure of the SPINOL skeleton.