Enantioselective de novo Construction of Pyran-2-one-fused Helicenoids via NHC Organocatalysis.

Helicenoids have attracted considerable interest in diverse research areas owing to their unique structural and electronic characteristics. However, catalytic asymmetric synthesis of helically chiral molecules has remained a formidable challenge. In particular, the organocatalytic enantioselective construction of heterohelicenoids has witnessed fairly limited progress, presumably due to the lack of rational design of competent substrates, the right choice of suitable reactions, and highly effective catalytic systems. In this study, we report the helicoselective and divergent synthesis of a new class of pyran-2-one-fused [5]helicenoids and [4]helicenoids through an NHC organocatalytic step-economical (3+3) annulation reaction. The protocol features broad substrate scope, ease of late-stage functionalization, and excellent stereo-control with enantioselectivities up to >99%. Moreover, the optical properties of the synthesized oxohelicenoids and their derivatives were characterized to explore their potential applications in material sciences.