Reductive coupling of isatins with ketones and aldehydes by low-valent titanium

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.

Enantioselective Construction of C4-Quaternary Quinolinones via Copper(II)-Catalyzed Asymmetric [1,3] O-to-C Rearrangement

An efficient asymmetric [1,3] O-to-C rearrangement of quinolin-2(1H)-ones enabled by a chiral bisoxazoline/copper complex has been developed. This strategy tolerated a wide range of substrates to provide a series of 1,4-dihydroquinoline-2,3-diones containing a quaternary stereocenter. A further cyclization of the [1,3] O-to-C rearrangement products was also realized, which led to various optically active 3,4-dihydroquinolin-2-ones with broad substrate scope.

Pd-Catalyzed Direct C-H Activation for the C5-Olefination of Methyleneindolinones

The direct C-H activation without directing groups can realize the para-selectivity, which is a powerful and concise approach for functionalization of arenes. Utilizing the strategy, a C5-olefination of methyleneindolinones has been successfully developed by palladium-catalyzed direct C-H activation, which provides an expeditious access to 5-vinylindolin-2-ones with high regioselectivity. The protocol is distinguished by a mild reaction system avoiding ligand and high temperature. The kinetic isotope experiments indicate that the C-H bond cleavage is the rate-limiting step.

Total Synthesis of (±)-11-O-Debenzoyltashironin via Palladium-Catalyzed 5-endo Ene-yne Cyclization Enabled trans-5-6 Ring Fusion

Illicium sesquiterpenes are a synthetically fascinating family of polycyclic natural products owing to their diversified pharmacological activities and structural complexity. Our cumulative efforts on developing a universal reductive coupling strategy toward stereoselective assembly of illicium sesquiterpenes recently resulted in a total synthesis of 11-O-debenzoyltashironin, a rare illicium sesquiterpene with a unique allo-cedrane carbon skeleton exhibiting prominent neurotropic activity, with complete stereochemical control. Our key tactics involved an unprecedented Pd(II)-catalyzed 5-endo ene-yne cyclization that directly allowed strained trans-5-6 ring fusion and a late-stage transannular McMurry coupling that furnished the compacted tetracyclic carbon skeleton rapidly.

One-pot synthesis of 3-hydroxy-2-oxindoles via acyloin rearrangements of 2-hydroxy-indolin-3-ones generated in situ from 2-alkynyl arylazides

A novel one-pot method to prepare 3-hydroxy-2-oxindoles via acyloin rearrangements of 2-hydroxy-indolin-3-ones generated in situ from 2-alkynyl arylazides has been described.

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.