Enantiopure [6]helicene containing an embedded seven‐membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid‐promoted intramolecular alkyne annulations of doubly axial‐chiral cyclization precursors. The helical handedness of the [6]‐ and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial‐to‐helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six‐membered ring formation was followed by the kinetically controlled seven‐ or six‐membered ring formation with or without helix‐inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]‐ and [7]helicenes with opposite helicity.
A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile-induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative p-extension of the chrysene units and produced quadruple (QH-2), triple (TH-2), and double (DH-2) helicenes containing [4]-and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes' structures were determined by X-ray crystallography and/or density functional theory calculations. The multiple TH-2 and DH-2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH-2, which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH-2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality. File list (2) download file view on ChemRxiv Ikai_ChemRxiv.pdf (1.17 MiB) download file view on ChemRxiv IkaiSI_ChemRxiv.pdf (23.71 MiB)
Enantiopure [6]helicene containing an embedded seven‐membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid‐promoted intramolecular alkyne annulations of doubly axial‐chiral cyclization precursors. The helical handedness of the [6]‐ and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial‐to‐helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six‐membered ring formation was followed by the kinetically controlled seven‐ or six‐membered ring formation with or without helix‐inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]‐ and [7]helicenes with opposite helicity.
<p>A series of multiple
helicenes was simultaneously synthesized in one step by intramolecular
cyclization of a single chrysene derivative containing two
2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the
aryl pendants. The electrophile-induced double cyclization with or without aryl
migrations proceeded efficiently under acidic conditions to afford annulative p-extension
of the chrysene units and produced quadruple (QH-<b>2</b>), triple (TH-<b>2</b>),
and double (DH-<b>2</b>)
helicenes containing [4]- and/or [5]helicene frameworks with dynamic and/or
static helicene chirality in one step. Three multiple helicenes’ structures
were determined by X-ray crystallography and/or density functional theory
calculations. The multiple TH-<b>2</b>
and DH-<b>2</b> helicenes were
separated into enantiomers because of the stable one and two [5]helicene
moieties, respectively, and showed intense circular dichroism and circularly
polarized luminescence. Although QH-<b>2</b>,
which comprises four [4]helicene subunits, was not resolved into enantiomers,
the TH-<b>2</b> enantiomers were
further separated into a pair of diastereomers at low temperature resulting
from their substituted [4]helicene chirality.</p>
<p>A series of multiple
helicenes was simultaneously synthesized in one step by intramolecular
cyclization of a single chrysene derivative containing two
2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the
aryl pendants. The electrophile-induced double cyclization with or without aryl
migrations proceeded efficiently under acidic conditions to afford annulative p-extension
of the chrysene units and produced quadruple (QH-<b>2</b>), triple (TH-<b>2</b>),
and double (DH-<b>2</b>)
helicenes containing [4]- and/or [5]helicene frameworks with dynamic and/or
static helicene chirality in one step. Three multiple helicenes’ structures
were determined by X-ray crystallography and/or density functional theory
calculations. The multiple TH-<b>2</b>
and DH-<b>2</b> helicenes were
separated into enantiomers because of the stable one and two [5]helicene
moieties, respectively, and showed intense circular dichroism and circularly
polarized luminescence. Although QH-<b>2</b>,
which comprises four [4]helicene subunits, was not resolved into enantiomers,
the TH-<b>2</b> enantiomers were
further separated into a pair of diastereomers at low temperature resulting
from their substituted [4]helicene chirality.</p>
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