Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO2 catalyst

Is It Possible to Obtain a Product of the Desired Configuration from a Single Knoevenagel Condensation? Isomerization vs. Stereodefined Synthesis

“…As for 3-benzylidene oxindole derivatives, there are attempts to develop stereoselective Knoevenagel protocols. It was found that CeO 2 can be an efficient catalyst for selective synthesis of (E)-3-alkenyl-oxindoles from oxindole and aldehydes, suggesting the heterogeneous catalytic C3-selective alkenylation reaction of oxindole for both aromatic and aliphatic aldehydes [31]. The use of a biocatalyst such as porcine pancreas lipase (PPL) in the Knoevenagel condensation of oxindole and various aromatic aldehydes allows one to perform the reaction with high selectivity towards the E configuration [32].…”

A Continuous‐Flow Method for the Transformation from Amides to Nitriles Catalyzed by CeO2 in Acetonitrile

“…The catalytic activities for the transformation from amides to nitriles were also higher when the calcination temperature was higher (400–600 °C). The catalytic activities of CeO 2 ‐700 °C and 800 °C were lower than that of CeO 2 ‐600 °C because the number of oxygen defect sites on the surface of CeO 2 decreased at calcination temperatures higher than 800 °C [9g] . For the efficient transformation from amides to nitriles, a balance between the crystallinity of CeO 2 and the number of oxygen defect sites on it may be important.…”

“…Generally, a higher calcination temperature leads to a larger crystal size and smaller surface area of CeO 2 . In particular, the number of oxygen defect sites in CeO 2 (low‐coordinated Ce sites) decreased significantly at calcination temperatures above 800 °C [9g] . We evaluated the effects of different calcination temperatures (400, 500, 600, 700, and 800 °C) on the transformation of 1 a under continuous‐flow conditions (Table 3).…”

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

“…Indeed, based on the methods developed, the condensation reaction of 2-oxindoles with ketones always adopted >100 °C, even up to 160 °C. 16,18,22 Recently, Siddiki and coworkers 23 reported a heterogeneous CeO 2 -catalyzed C3-selective alkenylation of 2-oxindole with aldehydes under solvent-free conditions. However, this catalytic method is only applicable to aldehydes.…”

“…Another approach is based on the installation of C3-alkenyl via Knoevenagel condensation reaction of 2-oxindoles with ketone substrates in the presence of abundant bases, such as pyridine, − piperidine, 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU), benzylamine (BnNH 2 ), solid base (KF/Al 2 O 3 ), and potassium hydroxide (KOH) (Scheme , eq 3). Indeed, based on the methods developed, the condensation reaction of 2-oxindoles with ketones always adopted >100 °C, even up to 160 °C. ,, Recently, Siddiki and coworkers reported a heterogeneous CeO 2 -catalyzed C3-selective alkenylation of 2-oxindole with aldehydes under solvent-free conditions. However, this catalytic method is only applicable to aldehydes.…”