Ambient Pressure Hydroformylation – A Key Step to meso-alkyl BODIPYs

Herein, a highly efficient five-step reaction sequence to meso-alkyl BODIPYs is presented. In our previous work, the hydroformylation of terminal alkenes was used to generate an aldehyde from an alkene via rhodium catalysis to be employed in a subsequent tandem reaction to obtain BODIPY dyes. However, the use of higher pressures and therefore autoclaves as well as their necessary equipment might limit others to use this method. The refined approach in this work employs ambient pressure hydroformylation, done in a simple Schlenk tube and using a CO/H2 balloon, as key step towards an easier meso-alkyl BODIPY synthesis. Additionally, the use of MTBE instead of chloroform as reaction solvent results in a greener approach. Readily available and easily synthesizable alkenes as well as different pyrrole building blocks can be used to extend the range of known alkyl-BODIPYs. The synthesis of 23 derivatives with overall yields of up to 67% demonstrates the wide applicability and advantages of the refined method.