ABSTRACT
A novel asymmetric (4 + 3) cycloaddition of indole-2,3-quinodimethanes in situ generated from 3-methyl-2-indolylmethanols with 3-indolylmethanols via chiral phosphoric acid catalysis has been established. The cycloaddition reaction exhibits a broad substrate scope affording the diverse enantioenriched cyclohepta fused diindoles in high yields with good enantioselectivities. Significantly, this work represents the first application of 3-methyl-2-indolylmethanols as 4C synthons instead of the commonly reported three-atom synthons in cycloaddition reactions.
ABSTRACT
A refined strategy has been developed to control the regioselective asymmetric (4+3) cyclization of α-(3-isoindolinonyl) propargylic alcohols with 2-indolylmethanols, utilizing chiral phosphoric acid catalysis. This innovative organocatalytic cyclization yields spiro isoindolinone-oxepine-fused indoles featuring a spiro-quaternary stereocenter in high yields and enantioselectivities, facilitated by the solvent of 1,1-dichloro-1-fluoroethane and the additive of hexafluoroisopropanol. Additionally, the photophysical properties of product 3k are examined, revealing bright fluorescence both in the solution and the solid state.
ABSTRACT
A novel chiral phosphoric acid-catalyzed tandem regioselective 1,6-addition/double intramolecular nucleophilic addition annulation of the propargylic 3-methyleneindoles in situ generated from α-indolyl propargylic alcohols with 2-indolylmethanols has been developed. The methodology afforded the new chiral trifluoromethyl pentalenobisindoles bearing an all-carbon quaternary stereogenic center in generally good yields with excellent enantioselectivities.
ABSTRACT
Rh(i) complex catalyzed dimerization of ene-vinylidenecyclopropanes took place smoothly to construct a series of products containing spiro[4,5]decane skeletons featuring a simple operation procedure, mild reaction conditions, and good functional group tolerance. In this paper, the combination of experimental and computational studies reveals a counterion-assisted Rh(i)-Rh(iii)-Rh(v)-Rh(iii)-Rh(i) catalytic cycle involving tandem oxidative cyclometallation/reductive elimination/selective oxidative addition/selective reductive elimination/reductive elimination steps; in addition, a pentavalent spiro-rhodium intermediate is identified as the key intermediate in this dimerization reaction upon DFT calculation.
ABSTRACT
A rhodium/silver synergistic catalysis has been established, enabling cycloisomerization/cross coupling of keto-vinylidenecyclopropanes (VDCPs) with terminal alkynes toward the regio- and enantioselective formation of diversified tetrahydropyridin-3-ol tethered 1,4-enynes in good yields and high ee values. In this synergistic catalysis, Rh(I) and Ag(I) catalysts selectively activate keto-VDCP substrates and terminal alkynes to generate the π-allyl Rh(III) complex of oxa-rhodacyclic intermediate and Ag alkynyl intermediate, respectively. The rapid transmetalation of alkynyl groups from Ag to Rh is proposed to play a key role in realizing the regioselective cleavage of the distal bond of the three-membered ring in this transformation.