An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Since 2004, chiral phosphoric acids (CPAs) have emerged as highyl efficient organocatalysts, providing excellent results in a wide reaction scope. In this review, the applications of CPA for enantioselective additions to CO and CN bonds are covered.

Advances in organocatalytic asymmetric reactions of vinylindoles: powerful access to enantioenriched indole derivatives

This review summarizes advances in vinylindole-based organocatalytic asymmetric reactions since 2008 and includes the applications of some methodologies in the total synthesis of natural products, points out remaining challenges in this research area.

Construction of chiral chroman scaffolds via catalytic asymmetric (4 + 2) cyclizations of para-quinone methide derivatives with 3-vinylindoles

The title reaction has been established in the presence of chiral phosphoric acid, affording chiral chroman derivatives bearing an indole moiety in high yields and with moderate to good stereoselectivities.

H-bonding vs Protonation of Alkynes in Regioselective Hydroamination Reactions: A Glimpse into the Reactivity of Arylogous Ynolethers and Ynamines

In this paper is described the competition and transition between hydrogen bonding and protonation of alkynes connected, on one side, to various aromatic rings and to chiral amino ester appendages on the other side. While the first mode of activation induced the cyclization into pyrrolidines, the protonation of the alkyne led preferentially to tetrahydropyridines due to the higher level of the highest occupied molecular orbital (HOMO) of the considered arylogous ynolethers and ynamines. The transition between H-bonding and protonation was observed with the alkyne substituted with 2-methoxyphenyl, for which the cyclization delivered either five- or six-membered rings depending on the temperature of the experiment. From there, the cyclization of dialkoxy- and trialkoxyphenyl-substituted alkynes into six-membered rings, i.e., tetrahydropyridines, was developed. When next applied to alkynylindoles, the same pattern of cyclization provided six-membered rings as an illustration of the reactivity of arylogous ynamines. Thanks to the high reactivity of the intermediate cationic species, weak nucleophiles such as NH-oxazolidinone participated efficiently in the hydroamination reaction of alkynylindoles. Pyrrolidines, tetrahydropyridines, and piperidines decorated with various aromatics and substituents were thus prepared in enantio- and stereoselective manner. Capitalizing on the enamine moiety of the azaheterocycles, the molecular diversity was extended through stereoselective oxidation and ring contraction processes.

Enantioselective synthesis of α-amino esters through Petasis borono-Mannich multicomponent reaction of potassium trifluoroborate salts

Enantioselective synthesis of α-amino esters have been achieved through the Petasis borono-Mannich multicomponent reaction using ( R)-BINOL-derived catalysts with stable heteroaryl and alkenyl trifluoroborate salts under mild conditions. The reaction provides direct access to optically active α-amino esters with moderate to good yields and enantioselectivities.

Palladium-catalyzed oxidative cyclization of aniline-tethered alkylidenecyclopropanes with O2: a facile protocol to selectively synthesize 2- and 3-vinylindoles

A facile and versatile palladium catalyzed oxidative cyclization of aniline-tethered alkylidenecyclopropanes with O₂ to selectively construct important synthetic intermediates 2- and 3-vinylindoles in moderate to good yields has been developed.

Highly enantioselective construction of carbazole derivatives via [4+2] cycloaddition of silyloxyvinylindoles and β,γ-unsaturated α-ketoesters

A highly enantioselective [4+2] cycloaddition between silyloxyvinylindoles and β,γ-unsaturated α-ketoesters was realized by an avaliable chiral N,N′-dioxide/yttrium triflate complex.

Highly efficient nitrogen chelated ruthenium carbene metathesis catalysts

Highly efficient nitrogen chelated ruthenium carbene metathesis catalysts containing an N-heterocyclic carbene (NHC) and a carbonyl group have been developed.

Asymmetric synthesis of highly functionalized tetrahydropyrans via a one-pot organocatalytic Michael/Henry/ketalization sequence

A diastereo- and enantioselective Michael/Henry/ketalization sequence to functionalized tetrahydropyrans is described. The multicomponent cascade reaction uses acetylacetone or β-keto esters, β-nitrostyrenes, and alkynyl aldehydes as substrates affording tetrahydropyrans with five contiguous stereocenters. Employing a bifunctional quinine-based squaramide organocatalyst, the title compounds are obtained in moderate to good yields (27-80%), excellent enantiomeric excesses (93-99% ee), and high diastereomeric ratios (dr > 20:1) after one crystallization.