Asymmetric systematic synthesis, structures, and (chir)optical properties of a series of dihetero[8]helicenes. Issue 8 (24th February 2021) - Yanagi, Tomoyuki
Abstract : A series of dihetero[8]helicenes have been synthesized in a stereoselective manner through an organosulfur-based synthetic strategy, which has enabled clarifying the effect of the endocyclic atoms on physical properties. Abstract : A series of dihetero[8]helicenes have been systematically synthesized in enantiomerically enriched forms by utilizing the characteristic transformations of the organosulfur functionality. The synthetic route begins with assembling a ternaphthyl common synthetic intermediate from 2-naphthol and bissulfinylnaphthalene through an extended Pummerer reaction followed by facile multi-gram-scale resolution. The subsequent cyclization reactions into dioxa- and dithia[8]helicenes take place with excellent axial-to-helical chirality conversion. Dithia[8]helicene is further transformed into the nitrogen and the carbon analogs by replacing the two endocyclic sulfur atoms via SN Ar-based skeletal reconstruction. The efficient systematic synthesis has enabled comprehensive evaluation of physical properties, which has clarified the effect of the endocyclic atoms on their structures and (chir)optical properties as well as the unexpected conformational stability of the common helical framework.