Asymmetric Cascade Dearomatization-Cyclization Reaction of Tryptamines with ß,γ-Alkynyl-α-imino Esters: Access to Hexahydropyrrolo[2,3-b]indole-Containing Tetrasubstituted α-Amino Allenoates.

An organocatalytic enantio- and diastereoselective synthesis of hexahydropyrrolo[2,3-b]indole-containing tetrasubstituted α-amino allenoates, exhibiting both axial and central chirality, has been accomplished via cascade dearomatization-cyclization reaction. The γ-addition to ß,γ-alkynyl-α-imino esters provides a library of densely substituted highly enantioenriched allenes in high yields and excellent stereoselectivities. In addition, the scope of this methodology has been extended to tryptophol as well. A scale-up reaction and synthetic transformations of the products were performed to demonstrate the practical usefulness of this approach.

Enantioselective Aminative Dearomatization of Indoles via Electrophilic 1,6-Addition of p-Quinone Diimides (p-QDIs).

Herein we report the first use of p-quinone diimide for the aminative dearomatization of 2,3-disubstituted indoles to furnish C3 aza-quaternary chiral indolenines. This approach, which proceeds via an electrophilic 1,6-addition of p-quinone diimide, allows the synthesis of an array of optically active aza-quaternary indolenines with high yields and excellent enantioselectivities. A one-pot approach of the same has also been established to further improve the synthetic accessibility of this protocol.

Organocatalytic Asymmetric Cascade Michael-Acyl Transfer Reaction between 2-Fluoro-1,3-diketones and 2-Hydroxynitrostyrenes.

An organocatalytic asymmetric cascade Michael-acyl transfer reaction of 2-hydroxynitrostyrenes and monofluorinated ß-diketones has been developed employing a cooperative catalytic system. A combination of quinine-derived bifunctional squaramide catalyst and achiral hydrogen bond donor cocatalyst was found to be the most effective for this reaction and provided the fluorinated acyl transfer products in high yields with good diastereo- and excellent enantioselectivities. Synthetic transformations have been demonstrated, including the synthesis of functionalized 2,3-dihydrobenzofurans and 1-pyrroline.

A Brønsted acid-catalyzed thioacid addition to in situ-generated aldimine for the synthesis of isoindolinones with the N,S-acetal framework.

A facile methodology was demonstrated for the synthesis of isoindolinones containing the N,S-acetal framework by employing a Brønsted acid catalyst with a three-component reaction. The reaction proceeded via the addition of thioacid to in situ-generated aldimine followed by lactamization, which involved the formation of one C-S bond and two C-N bonds under easily controlled and ambient reaction conditions. A variety of substituted isoindolinones were synthesized with up to 99% yields. Furthermore, the importance of this methodology was also justified by a gram-scale synthesis and demonstration of some interesting synthetic transformations.

Photoredox-Mediated Synthesis of Functionalized Sulfoxides from Terminal Alkynes.

A photoredox-mediated protocol for the synthesis of α-alkoxy-ß-ketosulfoxides and α,ß-dialkoxysulfoxides using alkynes, thiol, and alcohols is reported. This work presents a rare single-step synthesis of α-substituted sulfoxides, involving tandem introduction of a thiol and alcohol as a key enabling advancement. Furthermore, the method can be easily employed to access vinyl sulfoxides and ß-ketosulfoxides.