Enantioselective Organocatalytic Three-Component Vinylogous Michael/Aldol Tandem Reaction among 3-Alkylidene oxindoles, Methyleneindolinones, and Aldehydes

Highly regio- and stereoselective (3 + 2) annulation reaction of allenoates with 3-methyleneindolin-2-ones catalyzed by a planar chiral [2.2]paracyclophane-based bifunctional phosphine-phenol catalyst

A planar chiral [2.2]paracyclophane-based phosphine-phenol catalyst catalyzed the (3 + 2) annulation reaction of ethyl 2,3-butadienoate with 3-methyleneindolin-2-ones to produce 2,5-disubstituted cyclopentene-fused C3-spirooxindoles in high yields with high regio-, diastereo-, and enantioselectivities. This catalyst was suitable for reactions of not only benzylideneindolinones but also alkylideneindolinones, the chiral phosphine-catalyzed reactions of which have not yet been reported. Density functional theory calculations suggested that the formation of hydrogen bonds between the phenolic OH group of the catalyst and the allenoate carbonyl group, rather than between the OH group and the carbonyl group of indolinone, contributed to the formation of an efficient reaction space at the enantiodetermining step.

Metal-Free Regioselective Oxa-Michael Approach to Access Spirooxindole-Fused Tetrahydrofuran/Tetrahydropyran through [3 + 2]/ [4 + 2] Spirocyclization of Methyleneindolinones with Haloalcohols

An efficient one-pot metal-free, base-catalyzed method has been developed for the regioselective [3 + 2]/[4 + 2] annulation reactions of electrophilic methyleneindolinones with haloalcohols to furnish spirooxindole derivatives under mild reaction conditions. This reaction afforded the corresponding products with two contiguous stereocenters including a quaternary center in good to excellent yield (up to 95%) with moderate to good diastereoselectivities (up to 12.5:1 dr) with complete regioselectivity.

Asymmetric (3 + 3) and (4 + 2) Annulation Reactions of 2,3-Dioxopyrrolidines with 3-Alkylidene Oxindoles to Construct Diverse Chiral Heterocyclic Frameworks

Two substrate-controlled regiodivergent annulation protocols for 2,3-dioxopyrrolidines with 3-alkylidene oxindoles have been developed, which furnished a series of fused dihydropyrrolidone derivatives in high yields with excellent stereoselectivities. Plausible mechanistic pathways for both annulation reactions are proposed that [3 + 3] annulation reaction involves vinylogous Michael addition followed by intramolecular aldol cyclization, while [4 + 2] annulation reaction occurs through a vinylogous Michael addition and a subsequent intramolecular oxa-Michael cyclization.

Enantioselective Synthesis of Thiazolopyran Derivatives via a Direct Vinylogous Michael-oxa-Michael Sequence

An efficient diastereo- and enantioselective direct vinylogous Michael-oxa-Michael sequence between 5-alkenyl thiazolones and isopropylidene oxindoles has been developed. The reaction is catalyzed by a bifunctional squaramide catalyst that allows to access a wide range of densely substituted thiazolopyran derivatives containing a quaternary stereocenter. This protocol is flexible toward different sterically and electronically tuned substrates and is amenable to gram-scale synthesis and several synthetic transformations.

Regioselectivity Switch between Enantioselective 1,2- and 1,4-Addition of Allyl Aryl Ketones with 2,3-Dioxopyrrolidines

A vinylogous addition reaction of allyl aryl ketones with good yields and excellent regioselectivity catalyzed by squaramide catalysts has been developed. A series of chiral tertiary alcohols and bicyclic pyrrolidones could be synthesized in good to excellent yields, enantioselectivities, and diaseteroselectivities. Both experimental results and DFT calculations indicate that 1,2-addition reaction is favorable when the reaction is employed at a lower temperature, while the 1,4-addition/cyclization pathway is favorable when the reaction is employed at a higher temperature. Furthermore, the formation of compound 4 can potentially arise from either the 1,4-addition/cyclization pathway or retro-aldol reaction of compound 3, followed by subsequent 1,4-addition/cyclization.