Abstract:The first example of an enantioselective carbocyclization of an alkyne-containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2-hydroxynaphthyl substituent on the alkyne as ad irecting group constituted the key parameter enabling both efficient regioselective protonation of the carbon-carbon triple bond and chiral induction. The keyc ationici ntermediate could be depicted either as ac ationic vinylidene ortho-quinonem ethide or as tabilized vinyl cation. Atropoisomeric phenanthren… Show more
“…Thus, the use of chiral superacids, which are well established for numerous organocatalytic transformations, 78, 79 could be exploited to induce the electrophilic activation of the weakly basic alkyne function. The first example of an intramolecular enantioselective carbocyclization of an alkyne catalyzed by chiral Brønsted superacids was described in 2020 by Toullec et al 80 The key point was the use of o-biarylalkynes 253 as substrates, which possessed a 2-hydroxynaphtyl substituent as a directing group (Scheme 63). Indeed, this substituent induced (i) an increase of the basicity of the triple bond towards BA, (ii) a polarization of the alkyne that control the regioselectivity of the protonation during the formation of the vinyl cation, and (iii) the creation of a chiral environment between the substrate and the catalyst by Hbonding, which was mandatory to achieve high levels of enantioinduction.…”
Section: Enantioselectives Ba-catalyzed Cycloisomerization Of Aryl-al...mentioning
This review focuses on the carbocyclization reactions of alkyne-containing substrates catalyzed by Brønsted acids. The electrophilic activation occurs either by direct protonation of the alkyne or by formation of an intermediate cation that further reacts with the alkyne to give the vinyl cation key intermediate. A specific highlight will be put on the selectivity of the various methodologies described herein and on the mechanistic rationale.
“…Thus, the use of chiral superacids, which are well established for numerous organocatalytic transformations, 78, 79 could be exploited to induce the electrophilic activation of the weakly basic alkyne function. The first example of an intramolecular enantioselective carbocyclization of an alkyne catalyzed by chiral Brønsted superacids was described in 2020 by Toullec et al 80 The key point was the use of o-biarylalkynes 253 as substrates, which possessed a 2-hydroxynaphtyl substituent as a directing group (Scheme 63). Indeed, this substituent induced (i) an increase of the basicity of the triple bond towards BA, (ii) a polarization of the alkyne that control the regioselectivity of the protonation during the formation of the vinyl cation, and (iii) the creation of a chiral environment between the substrate and the catalyst by Hbonding, which was mandatory to achieve high levels of enantioinduction.…”
Section: Enantioselectives Ba-catalyzed Cycloisomerization Of Aryl-al...mentioning
This review focuses on the carbocyclization reactions of alkyne-containing substrates catalyzed by Brønsted acids. The electrophilic activation occurs either by direct protonation of the alkyne or by formation of an intermediate cation that further reacts with the alkyne to give the vinyl cation key intermediate. A specific highlight will be put on the selectivity of the various methodologies described herein and on the mechanistic rationale.
“…Stará and Starý 19 , 20 developed a Ni-catalysed enantioselective [2 + 2 + 2] cycloisomerisation of aromatic triynes to obtain the helicene derivatives. Toullec 3 , Yan 4 , Irie 5 , and Sparr 7 – 9 independently demonstrated efficient organocatalytic enantioselective cyclization of aryl-alkynes to construct valuable molecules containing axial or axial and helical stereogenic elements. Fig.…”
The simultaneous construction of two different chiralities via a simple operation poses considerable challenge. Herein a cationic gold-catalyzed asymmetric hydroarylation of ortho-alkynylaryl ferrocenes derivatives is developed, which enable the simultaneous construction of axial and planar chirality. The here identified TY-Phos derived gold complex is responsible for the high yield, good diastereoselectivity (>20:1 dr), high enantioselectivities (up to 99% ee) and mild conditions. The catalyst system also shows potential application in the synthesis of chiral biaryl compounds. The cause of high enantioselectivity of this hydroarylation is investigated with density functional theory caculation.
“…The development of atom-economical reaction with a nontoxic, affordable catalyst and universal functional group compatibility is thus highly desirable. 8 Recently, metal-free reactions, as an environmentally friendly and unique alternative to metal-mediated processes, have attracted much attention. Our research group has successively developed the metal-free annulations of ynamides with nitriles, 1,2-diazines, alkyne-nitriles and anthranils.…”
An efficient metal-free intramolecular hydroarylation reaction of alkynes is described here. A series of aryl and N-group attached alkynes generated the intramolecular hydroarylation products in high yields. In addition to...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
