Modular Synthesis of Organoboron Helically Chiral Compounds: Cutouts from Extended Helices

Two types of helically chiral compounds bearing one and two boron atoms were synthesized by a modular approach. Formation of the helical scaffolds was executed by the introduction of boron to flexible biaryl and triaryl derived from small achiral building blocks. All-ortho-fused azabora[7]helicenes feature exceptional configurational stability, blue or green fluorescence with quantum yields (phi(fl)) of 18-24 % in solution, green or yellow solid-state emission (phi(fl) up to 23 %), and strong chiroptical response with large dissymmetry factors of up to 1.12x10(-2). Azabora[9]helicenes consisting of angularly and linearly fused rings are blue emitters exhibiting phi(fl) of up to 47 % in CH2Cl2 and 25 % in the solid state. As revealed by the DFT calculations, their P-M interconversion pathway is more complex than that of H1. Single-crystal X-ray analysis shows clear differences in the packing arrangement of methyl and phenyl derivatives. These molecules are proposed as primary structures of extended helices.

Automated summary

Helically chiral compounds with one and two boron atoms were synthesized using a modular approach, showing exceptional configurational stability and fluorescence properties. The compounds are proposed as primary structures of extended helices, with potential applications in materials science.