The synthesis of substituted phosphathiahelicenes via regioselective bromination of a preformed helical scaffold: a new approach to modular ligands for enantioselective gold-catalysis

Abstract

Substituted phosphathiahelicenes have been prepared via a straightforward two-step procedure involving the regioselective bromination of a preformed helical scaffold, followed by palladium catalyzed coupling reactions. The new helicenes have been used as ligands in gold(i)-catalyzed [4+2] cyclizations of 1,6-enynes. The resulting dihydro-cyclopenta[b]naphthalene derivative was obtained in excellent yields and with up to 91% ee.

Gold-catalyzed enantioselective functionalization of indoles

“…Interestingly, the replacement of the unsubstituted catalyst (R= H) by an alkyne substitution (R=-C≡C-Ph) led to an increase of the enantioselectivities, as previously observed in other enantioselective gold-catalyzed processes. 54 The vinylgold key intermediate II is common to our work and Toste's report and traps the iminium function. Interestingly, the iminium is trapped here by the carbon bearing the gold atom, as opposed to previous work of Shi for which the similar intermediates evolved through the formation of a carbene and finally the generation of a five-membered ring (See Scheme 10, key step).…”

Recent Advances in the Development of Chiral Gold Complexes for Catalytic Asymmetric Catalysis

“…In 2014, Voituriez and Marinetti [33] firstly adopted phosphahelicenes as the chiral ligand of gold catalysts to achieve enantioselective cycloisomerization of enynes. In 2016, Voituriez and Marinetti [34] contributed another work featuring enantioselective [4+2] cycloaddition of hept‐6‐en‐1‐ynylbenzene derivatives. Employing modified phosphathiahelicenes as chiral ligands, the enantioselective cycloaddition afforded polycyclic dihydro‐cyclopenta[b]naphthalene derivatives in excellent yield (up to 99%) with high enantioselectivity (up to 91% ee) (Scheme 23).…”

Synthesis of [7]Helicene Enantiomers and Exploratory Study of Their Conversion into Helically Chiral Iodoarenes and Iodanes

“…Helicenes are polycyclic molecules composed of ortho-fused aromatic rings that confer an inherently chiral helical shape to their structures. [1][2][3][4] Owing to their uniques tructural, electronic and chiroptical properties, these compounds are the focus of considerable attention in variousf ields of research, [3][4][5] notably for their potential utility in asymmetricc atalysis, [6][7][8][9][10] molecular recognition, [11][12][13][14][15] supramolecular chemistry, [16][17][18] molecular machines design, [19][20][21][22][23] liquid crystal technology, [24][25][26][27] organic (opto)electronics, [28][29][30][31][32] as well as new materials. [33][34][35][36] Several of these applications necessitate access to optically pure helicenes.…”