Cyclodextrin host as a supramolecular catalyst in nonpolar solvents: stereoselective synthesis of (E)-3-alkylideneoxindoles

InCl3/TfOH-Mediated Convenient Synthesis of 3-Alkylideneoxindoles from 2-Oxindoles with 1,3-Diones, Ketones, or Aldehydes

Two efficient and convenient methods for the synthesis of 3-alkylideneoxindoles are described in this paper. The InCl3/TfOH-mediated tandem Knoevenagel condensation-deacylation sequence of various 2-oxindoles with 1,3-diones or acetoacetate furnished 3-alkylideneoxindoles in satisfactory to excellent yields (up to >99% yield). Employing the reaction system, the condensation of 2-oxindoles with ketones or aldehydes also proceeded smoothly to produce 3-alkylideneoxindoles. This protocol can be amenable to scale up. The effect of acids on this condensation reaction and intermolecular competition experiments were investigated to understand the aspect of the reaction.

Non-Palladium-Catalyzed Approach to the Synthesis of (E)-3-(1,3-Diarylallylidene)Oxindoles

Two novel synthetic approaches for synthesizing (E)-3-(1,3-diarylallylidene)oxindoles from oxindole were developed. All previously reported methods for synthesizing 3-(1,3-diarylallylidene)oxindoles utilized palladium-catalyzed reactions as a key step to form this unique skeleton. Despite high efficiency, palladium-catalyzed reactions have limitations in terms of substrate scope. Especially, an iodoaryl moiety cannot be introduced by the previous methods due to its high reactivity toward the palladium catalyst. Our Knoevenagel/allylic oxidation/Wittig and Knoevenagel/aldol/dehydration strategies complement each other and show broad substrate scope, including substrates with iodoaryl groups. The current methods utilized acetophenones, benzylidene phosphonium ylides, and benzaldehydes that are commercially available or easily accessible. Thus, the current synthetic approaches to (E)-3-(1,3-diarylallyldiene)oxindoles are readily amendable for variety of oxindole derivatives.

A transition-metal-free, base-promoted annulation/ring-cleavage/ring-reconstruction cascade reaction: a facile access to N-protection free indole-indenones

An unprecedented base-promoted reaction of 2-halogenated arylglyoxals with 2-oxindoles is accomplished under metal-free conditions, furnishing a wide range of biologically important (NH)-indeno[2,1-b]indol-6(5H)-ones in useful to good yields.

Indium triflate catalysed 3-aza-Cope rearrangement of amino acid derived α,β-unsaturated esters to alkylidene oxindoles

The first examples of amino acid derived α,β-unsaturated esters to Z-alkylidene oxindoles via 3-aza-Cope rearrangement using In(OTf)₃ are reported.

Synthesis of Functionalized 6-Hydroxy-2-oxindole Derivatives by Phenoxide Cyclization

An apparent intramolecular cross-dehydrogenative coupling of N-(3-hydroxy)monoanilide of maleic esters comprising base promoted phenoxide cyclization and subsequent base-mediated aerobic oxidation was developed to synthesize a variety of 2-(6-hydroxy-2-oxoindolin-3-ylidene)acetate derivatives. The isolation of intermediate cyclized products during the large scale reactions and their ready dehydrogenation with 1 equiv of base support this proposed two-step path.