Point-to-helical chirality transfer in the diastereoselective synthesis of boron dipyrromethenes (BODIPYs) Aminah Almarshad 1,2 , Felicity Frank 1 , Julian Knight 1 and Michael Hall* 1 1 Newcastle University, UK, 2 Imam Abdulrahman Bin Faisal University, Saudi Arabia The boron dipyrromethenes (BODIPYs) are a class of fluorescent organic dyes that have found use in numerous applications such as biological imaging, solar cells, and photodynamic therapy. 1 Our research group is concerned with the design and investigation of new synthetic routes to produce helically chiral BODIPYs, which have the ability to emit circularly polarized luminescence (CPL), for future application in CPL imaging. The synthesis of helically chiral BODIPYs is challenging, and previous routes often rely on resolution of racemic mixtures by chiral HPLC. 2 Here we demonstrate the first use of enantiopure amino acid and amino alcohol substituents as chiral auxiliaries, capable of controlling the formation of helical chirality in the BODIPYs through a point-to-helical chirality transfer mechanism. Our synthetic strategy involves the introduction of enantiopure amino acid or amino alcohol chiral auxiliaries via S N Ar chemistry, followed by helicity creation through a boron chelation reaction. 3 Point-to-helical chirality transfer has been achieved with high diastereomeric excess (up to 84%), and with the relative stereochemistry of the products confirmed by single crystal X-ray diffraction (SCXRD). This novel synthetic strategy has allowed us to access a range of helically chiral BODIPYs for future chiroptical analysis.
References 1. Treibs and F. H. Kreuzer, Justus Liebigs Ann. Chem ., 1968, 718 , 208–223. 2. R. B. Alnoman, S. Rihn, D. C. O’Connor, F. A. Black, B. Costello, P. G. Waddell, W. Clegg, R. D. Peacock, W. Herrebout, J. G. Knight and M. J. Hall, Chem. Eur. J ., 2016, 22 , 93–96. 3. F. J. Frank, P. G. Waddell, M. J. Hall and J. G. Knight, Org. Lett ., 2021, 23 , 8595-8599.
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