Stereoselective Cyclopropanation of Boron Dipyrromethene (BODIPY) Derivatives by an Organocascade Reaction

The synthesis of enantiopure chiral boron dipyrromethenes (BODIPYs) is of importance due the intrinsic properties of BODIPYs as fluorophores that could be used as probes for molecular sensing. The present study reports an asymmetric organocatalytic cascade reaction of meso-chloromethyl BODIPY derivatives with alpha,beta-unsaturated aldehydes catalyzed by a chiral secondary amine. The corresponding BODIPY-derived cyclopropanes were produced in isolated yields 66-98%, and with diastereomeric ratios 3/2->20/1, and 92-99% ee for major diastereomer. The synthetic utility of the protocol was exemplified on a set of additional transformations of the corresponding optically pure compounds. In addition, a study explaining the reaction mechanism (DFT computations) and photophysical characterization of all enantioenriched products were accomplished.

Automated summary

A new asymmetric organocatalytic cascade reaction was reported for the synthesis of enantiopure chiral boron dipyrromethenes (BODIPYs), with high isolated yields and enantiomeric excesses. The method showed synthetic versatility and was successfully applied to a series of additional transformations of the corresponding optically pure compounds.