Enantioselective Cyclization by a Hexacoordinated Chiral Hydrogen Phosphate

Key words

chiral counteranion - phosphates - Pictet−Spengler-type cyclization

Significance

The Ooi group reports a Pictet− Spengler-type cyclization catalyzed by the Brøn­sted acid 1·H. The presented chiral hexacoordinated phosphate ion consists of two N,N,O-tridentate backbones, including 1,2-diphenylethylene-diamine as a readily available chiral source. The catalyst is prepared by deprotonation of a phenol followed by cation exchange. The authors obtained a single-crystal X-ray structure of 1·HNEt₃ which confirmed its octahedral P(V) core.

Comment

The authors demonstrate the catalytic activity of 1 as hydrogen phosphate. Although the substrate scope is limited, it is noteworthy that the hexacoordinated phosphate can indeed control the enantioselectivity. More mechanistic studies and control experiments would be highly appreciated to further understand and expand the presented transformation.