Single electron transfer reactions and the synthesis of Chiral BODIPYs

Abstract

This thesis is divided into two parts. Part one covers single electron transfer reactions of electron deficient carbonyls and Grignard reagents whilst part two discusses our progress towards the synthesis of axially chiral BODIPYs.

Part 1: Reaction of 2,2,2-trichloro-1-arylethanones with PhMgBr resulted in a reduction to give 2,2-dichloro-1-arylethanones. We have shown through by-product analysis and EPR measurement that this reaction proceeds through a Single Electron Transfer (SET) mechanism with PhMgBr acting as the electron donor. Addition of electrophiles to the intermediate magnesium enolates, formed in the reaction, gave aldol, Claisen and aldol/Tishchenko products.

Scheme 1 Reaction of PhMgBr with 2,2,2-trichloro-1-arylethanones followed by addition of an electrophile Scheme 2 General route for the synthesis of axially chiral BODIPYs

Resolution of a racemic axially chiral BODIPY was performed by preparative chiral HPLC.

Scheme 3 Resolution of racemic-BODIPYs using HPLC

Electronic Circular Dichroism (ECD) spectroscopy and measurements showed

that the separated BODIPYs were enantiomeric. Comparison of measured and computational ECD spectra allowed assignment of the absolute stereochemistry.

Part 2: A number of BODIPYs have been synthesised which demonstrated axial chirality, based on the restricted rotation of ortho-aryl meso substituents