Transition metal catalysed synthesis of tetrahydro derivatives of [5]-, [6]- and [7]helicene

Enantioselective Helicene Synthesis by Rhodium-Catalyzed [2+2+2] Cycloadditions

“…Interestingly, the desired intramolecular [2+2+2] cycloadditions of 1a and 1b proceeded by using not the biaryl bisphosphine but a nonbiaryl bisphosphine, (R,R)-Me-Duphos, as a ligand to give the corresponding [7]helicene-like molecules 2a and 2b in good yields and ee values (Scheme 3).…”

“…4 Among them, a [2+2+2] cycloaddition strategy is highly attractive because of its convenient operation and applicability to the enantioselective synthesis. 5,6 In 1999, Starý, Stará, and co-workers reported the enantioselective synthesis of [6]helicene-like molecules via the nickel(0)/axially chiral biaryl monophosphine complex-catalyzed [2+2+2] cycloaddition of triynes, while enantioselectivity was moderate and the enantioselective synthesis of sterically more demanding [7]helicene-like molecules did not succeed (Scheme 1). 7,8 On the other hand, our research group found that cationic rhodium(I)/biaryl bisphosphine complexes are highly active and selective catalysts for the [2+2+2] cycloaddition reactions.…”

“…5,6 In 1999, Starý, Stará, and co-workers reported the enantioselective synthesis of [6]helicene-like molecules via the nickel(0)/axially chiral biaryl monophosphine complex-catalyzed [2+2+2] cycloaddition of triynes, while enantioselectivity was moderate and the enantioselective synthesis of sterically more demanding [7]helicene-like molecules did not succeed (Scheme 1). 7,8 On the other hand, our research group found that cationic rhodium(I)/biaryl bisphosphine complexes are highly active and selective catalysts for the [2+2+2] cycloaddition reactions. 9,10 We then applied these complexes to chemo-, regio-, and enantioselective [2+2+2] cycloaddition reactions for the construction of axial, 11 planar, 12 and central chiralities.…”

“…The more sterically encumbered reaction, the rhodium-catalyzed enantioselective double intramolecular [2+2+2] cycloaddition of a 2-naphthol-linked hexayne, also proceeded to give a [11]helicene-like molecule with high ee value, although the product yield was low. Not only intramolecular cycloaddition reactions but also intermolecular ones were accomplished by combinations of electron-rich tetraynes and electron-poor diynes to give [7]-and [9]helicene-like molecules and [7]helicenes in varying yields and ee values. …”

“…The rhodium-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2-naphthol-linked triynes afforded [7]helicene-like molecules in good yields and ee values. The more sterically encumbered reaction, the rhodium-catalyzed enantioselective double intramolecular [2+2+2] cycloaddition of a 2-naphthol-linked hexayne, also proceeded to give a [11]helicene-like molecule with high ee value, although the product yield was low.…”