Palladium‐Catalyzed Construction of Spirooxindoles by Arylative Cyclization of 3‐(γ,δ‐Disubstituted)allylidene‐2‐Oxindoles

Abstract

The palladium-catalyzed, one-pot arylative cyclization of 3-(g,d-disubstituted)allylidene-2oxindoles afforded spirodihydronaphthalene-2-oxindole frameworks via an oxidative Heck arylation (Fujiwara-Moritani reaction), an allylic palladium migration, and an aryl C À H bond functionalization/ arylation cascade of reactions. This is a first example of the palladium-catalyzed oxidative arylation and an aryl C À H bond functionalization/arylation cascade reaction which involves an electrophilic arylative quenching of a p-allylpalladium intermediate and a regio-controlled aryl C À H bond activation assisted by a weak palladium-arene interaction.

Diastereoselective Synthesis of Six‐Membered Carbocyclic Spirooxindoles via 6π‐Electrocyclization of 3‐Dienylidene‐2‐ oxindoles

“…The starting material 3a ‐ ZEE was required in order to obtain the other stereoisomer 5a ; however, 3a ‐ ZEE could not be isolated as mentioned above. In our previous paper, we observed a palladium‐catalyzed isomerization of the C α C β double bond of 3‐(γ,δ‐disubstituted)allylidene‐2‐oxindoles 5. Thus, we assumed that the C α C β double bond of 3a ‐ EEE could also be isomerized in the presence of a catalytic amount (5 mol%) of Pd(OAc) 2 at elevated temperature to furnish 3a ‐ ZEE .…”

“…The synthesis of starting material was carried out by the Wittig reaction between isatin and the phosphorus ylide generated from the corresponding Morita–Baylis–Hillman (MBH) bromide of cinnamaldehydes,5–8 as shown in Scheme . The triene 3a ‐ EEE was isolated in good yield (79%) as a major product 6.…”

“…To our delight, compound 5a was isolated as a major product (73%) along with a low yield of 4a (19%). Compound 5a could be formed most likely by a thermal 6π‐electrocyclization of 3a ‐ ZEE which is formed in‐situ by a palladium‐catalyzed isomerization process via the intermediate I 5,11. During the whole reaction progress the formation of 3a ‐ ZEE was not observed on TLC, although 5a was a major product.…”

“…syn ‐Carbopalladation of 5a with phenylpalladium species afforded the intermediate II , and a subsequent syn β‐H elimination produced 6a in good yield (81%). The stereo‐ and regioselective formation of II might be ascribed to the stabilization of palladium center by chelation with the carbonyl group of oxindole moiety 5,14f. In addition, the product 6a could be obtained from 3a ‐ EEE directly in good yield (75%) via the sequential palladium‐catalyzed isomerization of 3a ‐ EEE to 3a ‐ ZEE ( vide supra ), 6π‐electrocyclization to form 5a , and the final palladium‐catalyzed oxidative phenylation to 6a .…”

“…Very recently, we reported the palladium‐catalyzed construction of spirooxindoles by arylative cyclization of 3‐(γ,δ‐disubstituted)allylidene‐2‐oxindoles 5. A sequential palladium‐catalyzed oxidative arylation, allylic palladium migration, and an aryl CH bond functionalization/arylation cascade reaction provided an interesting spirodihydronaphthalene‐2‐oxindole [Scheme , Eq.…”