λ⁵‐Phospha[7]helicenes: Synthesis, Properties, and Columnar Aggregation with One‐Way Chirality

Abstract

Einbahnstraße: Eine neue Familie von λ5‐Phospha[7]helicenen, die eindimensionale säulenartige Stapel im festen Zustand bilden, wurde synthetisiert (siehe Schema). Benachbarte Stapel haben entgegengesetzte Dipolrichtungen. Im Fall des Helicens auf Basis von racemischem Phospholsulfid bestehen Säulen mit einer der beiden Dipolrichtungen aus dem einen Enantiomer, Säulen mit entgegengesetzter Dipolrichtung aus dem anderen.

Heterohelicenes with Embedded P‐Chiral 1H‐Phosphindole or Dibenzophosphole Units: Diastereoselective Photochemical Synthesis and Structural Characterization

“…Biological applications and the use of helicenes as chiral auxiliaries have also been envisioned. So far, synthetic strategies have been reported by the groups of Tanaka and Nozaki, which make use of Rh I /H 8 -BINAP-catalyzed (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) enantioselective [2+2+2] cyclization [4] and palladium-promoted intramolecular P-arylation [5] reactions as the key steps, respectively. Moreover, it opens up an even more extended range of properties and applications of these compounds, based on the potential coordination of the phosphorus atoms to a variety of transition metals.…”

ChemInform Abstract: Phosphathiahelicenes: Synthesis and Uses in Enantioselective Gold Catalysis.

“…[3c] The phosphines used in these processes display phosphorus functions grafted on helical scaffolds. Following to the pioneering work of Tanaka [5] and Nozaki, [6] we have introduced recently a new design for helical phosphorus ligands where a trivalent phosphorus function is embedded in the helical structure itself, as a phosphole unit. [7] In these series, the so-called HelPhos ligands (Figure 1) afforded excellent catalysts for gold-promoted enantioselective cycloisomerizations with ee values up to 86 % for the conversion of N-tethered 1,6-enynes into 3-azabicyclo[4.1.0]heptenes.…”

1H‐Phosphindoles as Structural Units in the Synthesis of Chiral Helicenes

“…Trivalent phosphorus functions and the related metal complexes are easily designed to tune the electronic and physicochemical properties of helicenes, [10] as well as to offer a wide range of potential uses in organometallic chemistry and catalysis. [13] We intend to disclose here: a) the first diastereo-and enantioselective access to [6]-and [7]helicenes in which the fused ring sequence ends with a phosphole unit; b) the structural and chiroptical properties of enantiomerically pure derivatives of this class; c) the enantiospecific self-assembly of columnar arrangements in the solid state; and d) the photochemical [2+2] annulations of phosphole-fused [6]helicenes into dimeric helical structures.When targeting helicenes where phosphorus is embedded within the helical framework itself, we envisioned 1Hphosphindole oxides as suitable building blocks and have adapted the classical helicene synthesis, based on the photochemical cyclization/dehydrogenation of diarylolefins, to these substrates. So far, most phosphorus derivatives having helical chirality display polyaromatic (or heteroaromatic) helical scaffolds with pendant phosphorus functions (phosphites, [2a, 6b, 11] trivalent phosphines and phosphine oxides, [6a, 12] phospholes, [10a,b] etc.).…”

“…Helicenes of this class are unknown to date, whereas phosphahelicenes, wherein phosphorus is embedded in the internal section of the helical framework, have been reported only recently by Tanaka and co-workers and Nozaki and co-workers. [13] We intend to disclose here: a) the first diastereo-and enantioselective access to [6]-and [7]helicenes in which the fused ring sequence ends with a phosphole unit; b) the structural and chiroptical properties of enantiomerically pure derivatives of this class; c) the enantiospecific self-assembly of columnar arrangements in the solid state; and d) the photochemical [2+2] annulations of phosphole-fused [6]helicenes into dimeric helical structures.When targeting helicenes where phosphorus is embedded within the helical framework itself, we envisioned 1Hphosphindole oxides as suitable building blocks and have adapted the classical helicene synthesis, based on the photochemical cyclization/dehydrogenation of diarylolefins, to these substrates. [14] Our starting materials are the olefins 5 which combine a 1H-phosphindole unit and a benzo[c]phenanthrene fragment.…”

“…Helicenes of this class are unknown to date, whereas phosphahelicenes, wherein phosphorus is embedded in the internal section of the helical framework, have been reported only recently by Tanaka and co-workers and Nozaki and co-workers. [13] We intend to disclose here: a) the first diastereo-and enantioselective access to [6]-and [7]helicenes in which the fused ring sequence ends with a phosphole unit; b) the structural and chiroptical properties of enantiomerically pure derivatives of this class; c) the enantiospecific self-assembly of columnar arrangements in the solid state; and d) the photochemical [2+2] annulations of phosphole-fused [6]helicenes into dimeric helical structures.…”