A HELIXOL‐Derived Bisphosphinite Ligand: Synthesis and Application in Gold‐Catalyzed Enynes Cycloisomerization

Abstract

The synthesis, optical resolution through derivatization, characterization, and utilization of a new helical bis(phosphinite gold) complex derived from HELIXOL are described. By using an efficient cobalt catalyst, neither irradiation nor high catalytic loading was required to access the helicene of interest. The latter was phosphorylated to afford a new chiral ligand that was studied. Especially, treatment with AuCl(SMe2) gives a dinuclear gold complex that was used in cycloisomerization reactions.

Gold-Catalyzed Synthesis of Small Rings

“…All in all, the 6- endo -dig cycloisomerizations of O - and N -tethered 1,6-enynes to products 134a , 134b , and 134c have become standard reactions to test the performance of new gold complexes, such as 135 , 397 136 , 398 137 , 399 and 138 ( 400 ) ( Scheme 38 ). Enantioselective variants have been achieved employing chiral mono- or dinuclear Au(I) complexes 139 , 401 402 140 , 403 , 404 141 , 405 142 , 406 143 , 407 144 , 408 145 , 409 146 , 410 and 147 ( 411 ) ( Scheme 39 ).…”

Helical Bisphosphinites in Asymmetric Tsuji‐Trost Allylation: a Remarkable P:Pd Ratio Effect

“…Saturated bismethoxyhelicene 6h (Scheme 2) was synthesized according to described literature procedures. [9,10] Synthesis of heterohelicene 6i began with the Sonogashira cross-coupling between alkyne 2i and iodide 3i to provide 4i. Cleavage of both methoxymethyl (MOM) protecting groups in 4i proved nontrivial as the free phenol function tends to cyclize and yield the corresponding benzofuran.…”

“…We attributed these very low enantiomeric excesses to the linear coordination of gold(I) together with the absence of aurophilic interactions in the active catalytic intermediate. [9] Therefore, we envisaged moving from linear coordination to a square planar complex, in order to maximize steric hindrance around the metal center and by consequence optimize the enantioinduction. Moreover, in order to increase the flexibility of the helicene and to tune the electronics of the template, we completed the study by synthesizing non-rearomatized helix 1h as well as an oxygenated analog 1i (Scheme 1).…”

C2-Symmetric P-Stereogenic Ferrocene Ligands with Heavier Chalcogenophosphinous Acid Ester Donor Sites

“…In general, chalcogeno phosphinous acid esters are prepared from diorganohalophosphanes by reaction with the corresponding metalchalcogenolate [ 1 , 4 ]. As an alternative, oxidative cleavage of a diphosphane with dichalcoganes (alias dichalcogenides) has also been reported [ 2 , 3 ].…”