Synthesis of Methoxy Substituted Centrally Chiral Triynes as Precursors of Functionalised Nonracemic Helicene-Like Compounds

Abstract

A modular synthesis of a series of methoxy substituted optically pure aromatic triynes (-)-(S)-5-9 and (-)-(R)-10 is presented. It relies on key operations such as substitution of benzylic bromine with an alkoxy group and aryl-alkyne coupling reaction to combine appropriate methoxy substituted benzene/naphthalene building blocks and chiral alkynol synthons such as (-)-(2S)-but-3-yn-2-ol and (-)-(1R)-1-phenylprop-2-yn-1-ol. The triyne molecules comprise a diphenylacetylene, 1-(phenylethynyl)naphthalene or 1,1'-ethyne-1,2-diyldinaphthalene core unit. They are intended to serve as [2+2+2] cyclisation precursors of methoxy substituted nonracemic helicene-like compounds with a penta-, hexa- and heptacyclic helical scaffold.

Helicenes: Synthesis and Applications

“…Recently, anthra[11]helicene 120 ,, was prepared in one step in nearly 40% yield by double cycloisomerization involving the building of six new rings (Scheme ) . This methodology is very practical not only because of the high efficiency (100% atom economy, good to excellent yields, rapid reaction) but also because of the modular assembly character whereby different functional groups can be introduced in the aromatic and alkyl moieties to afford nonsymmetric and multifunctionalized (tetrahydro)helicenes. Consequently, many substituted helicenes ,, and helicene-like molecules, such as Vollhardt’s heliphenes, Tanaka’s [9]helicene-like molecule, Teplý’s helquats, and Carbery’s helicenoidal DMAP catalyst, have been synthesized using this approach.…”

One hundred years of helicene chemistry. Part 1: non-stereoselective syntheses of carbohelicenes

“…We will also report the asymmetric versions of those methods and other diastereoselective reactions for producing non-racemic helicenes in Part 2 of our series of reviews on carbohelicenes. [185][186][187][188][189] To top it all off and by taking advantage of this elegant synthetic route, a fully conjugated [11]helicene was recently synthesized by Stary ´and coworkers from a double intramolecular [2p + 2p + 2p] cycloisomerization of a hexayne by using this non-photochemical route (Scheme 49). 190 Up to now, this is one of the longest, fully conjugated carbohelicene, synthesized without using an oxidative photocyclodehydrogenation reaction.…”

On the Origin of Diastereoselectivity in [2 + 2 + 2] Cycloisomerization of Chiral Triynes: Controlling Helicity of Helicene-like Compounds by Thermodynamic Factors

“…Synthesis of optically pure aromatic triynes ( S )-(−)- 1 − 5 and ( R )-(−)- 6 (Figure ) containing an asymmetric carbon atom of known absolute configuration was accomplished using the general methodology we published previously 1 Model triynes for diastereoselective [2 + 2 + 2] cycloisomerization. …”