New Synthesis of Octahelicene Involving Non-Interconvertible<i>Dl</i>- Intermediates

Martin, Richard; Cosyn, J.P.

doi:10.1080/00397917108082706

Cited by 16 publications

(4 citation statements)

References 10 publications

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“…In a next step, alcohols ( P )‐(+)‐ 12 and ( M )‐(–)‐ 12 were oxidized with Dess–Martin periodinane to the corresponding aldehydes ( P )‐(+)‐ 13 and ( M )‐(–)‐ 13 , respectively, which were subsequently subjected to a Wittig reaction to give ( P )‐(+)‐ 2 and ( M )‐(–)‐ 2 , respectively. Helicene derivatives 11 – 13 (for their ECD spectra, see Section 2.4 in the Supporting Information) had previously been prepared by different, photocyclodehydrogenation‐based methodology 26,27. Olefin metathesis of ( P )‐(+)‐ 2 and ( M )‐(–)‐ 2 by using the sterically less‐demanding Stewart–Grubbs catalyst28 ( 14 ) afforded ( E )‐( P , P )‐(+)‐ 1 and ( E )‐( M , M )‐(–)‐ 1 , respectively, in 70 % yield.…”

Section: Resultsmentioning

confidence: 99%

“…( P )‐(+)‐[6]Helicene‐2‐ylmethanol [( P )‐(+)‐12] and ( M )‐(–)‐[6]Helicene‐2‐ylmethanol [( M )‐(–)12]: 26,27 LiAlH 4 (26 mg, 0.68 mmol) in Et 2 O (5 mL) was treated with a solution of racemic (±)‐ 11 (124 mg, 0.321 mmol) in benzene/Et 2 O (1:1, 3 mL) at 22 °C, and the mixture was stirred for 3 h at 40 °C. The mixture was cooled in an ice bath, a concentrated aqueous solution of Na 2 SO 4 (10 mL) was added dropwise, and stirring was continued for an additional 0.5 h at 22 °C.…”

Section: Methodsmentioning

confidence: 99%

“…Separation of the phases, washing the aqueous phase with CH 2 Cl 2 (3 × 10 mL), drying the combined organic phases (Na 2 SO 4 ), and evaporating the solvent gave pure (±)‐ 12 (110 mg, 96 %) as a racemic mixture, m.p. 134–136 °C {ref 26. 135–136 °C}.…”

Section: Methodsmentioning

confidence: 99%

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Electronically Connected [n]Helicenes: Synthesis and Chiroptical Properties of Enantiomerically Pure (E)‐1,2‐Di([6]helicen‐2‐yl)ethenes

et al. 2013

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We synthesized stilbenoid (E)‐(P,P)‐ and (E)‐(M,M)‐[6]helicene dimers in enantiomerically pure form as part of a program aimed at the exploration of new strategies for the synthesis of large helicenes. The [2+2+2] cyclotrimerization of suitable triynes, reported by Starý and co‐workers, was applied for the preparation of a racemic 2‐hydroxymethylated [6]helicene precursor, which was conveniently resolved by HPLC on a chiral stationary phase. Two optically active helicenes were subsequently connected to the stilbenoid dimer by olefin metathesis. Electronic circular dichroism (ECD) studies of the stilbenoid ethen‐1,2‐diyl‐linked dimer revealed bathochromically shifted ECD bands with exceptionally large Cotton effects relative to those of the monomeric [6]helicenes or to that of a dimeric [6]helicene with a saturated ethan‐1,2‐diyl linker. These comparative studies, complemented by computational investigations, show that the pronounced chiroptical properties of the stilbenoid dimer originate from π‐conjugation between the two [6]helicene moieties and from the rigidity that results from conjugation. All attempts to form (P)‐[13]helicene by photocyclodehydrogenation of the stilbenoid (P,P)‐dimer were unsuccessful.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Electronically Connected [n]Helicenes: Synthesis and Chiroptical Properties of Enantiomerically Pure (E)‐1,2‐Di([6]helicen‐2‐yl)ethenes

et al. 2013

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“…[1] Several synthetics trategies toward helicenes and their homologues have been developed to date, among which oxidative photocyclizations of stilbene-type (Ar-CH = CH-Ar')c ompounds that afford phenanthrene frameworks represent the most commonlye ncountered, mostly on account of their procedural simplicity. [2] For example, [16]helicene, which is currently the longest carbohelicene reported, was successfully synthesized by multiple photocyclizations. [3] However,t he same procedure cannot be applied to the synthesis of azahelicenes from imine-type precursors (Ar-CH = N-Ar'), [4] because such photocyclizations requireaZ geometry.…”

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Azahelicenes from the Oxidative Photocyclization of Boron Hydroxamate Complexes

Murase

Suto

Suzuki

2017

Chemistry An Asian Journal

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Aromatic hydroxamic acids (Ar-CO-NOH-Ar') were used as bidentate chelating ligands to generate the corresponding boron hydroxamate complexes, which were subsequently transformed into nitrogen-containing helicenes (azahelicenes) using an oxidative photocyclization method that is frequently used for stilbene-type (Ar-CH=CH-Ar') precursors of carbohelicenes. The nitrogen atom of the hydroxamate linker was thus directly embedded into the helicene core without using nitrogen-containing aromatic rings in the stilbene-type precursors. In a batch photoreaction, aza[4]helicenes were readily and efficiently prepared, but aza[6]helicenes underwent severe decomposition upon irradiation. Alternatively, a continuous flow photoreactor was employed to furnish an amide-type aza[6]helicene.

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Photocyclization of Stilbenes and Related Molecules

1984

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On irradiation in solution with ultraviolet (UV) light, cis ‐stilbene undergoes reversible photocyclization to give trans ‐4a,4b‐dihydrophenanthrene, an intermediate that can be trapped oxidatively with hydrogen acceptors such as iodine, oxygen, or tetracyanoethylene to give phenanthrene in high yield. This type of photoreaction occurs with a wide range of substituted stilbenes and related molecules, including various polycyclic and heterocyclic analogs; in addition, certain systems with a single heteroatom (nitrogen, oxygen, or sulfur) in place of the central π bond undergo photocyclization, creating a new five‐membered heterocyclic ring. In some of these photocyclizing systems, the transient dihydroaromatic intermediates are trapped without added oxidants by the elimination of suitable leaving groups or by various hydrogen shifts. Photocyclization is the preferred method for the synthesis of many different polynuclear aromatic systems. The discovery and early development of stilbene photocyclization has been surveyed, and several other general reviews have appeared.

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New Synthesis of Octahelicene Involving Non-InterconvertibleDl- Intermediates

Cited by 16 publications

References 10 publications

Electronically Connected [n]Helicenes: Synthesis and Chiroptical Properties of Enantiomerically Pure (E)‐1,2‐Di([6]helicen‐2‐yl)ethenes

Electronically Connected [n]Helicenes: Synthesis and Chiroptical Properties of Enantiomerically Pure (E)‐1,2‐Di([6]helicen‐2‐yl)ethenes

Azahelicenes from the Oxidative Photocyclization of Boron Hydroxamate Complexes

Photocyclization of Stilbenes and Related Molecules

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