Asymmetric [4 + 3] Annulations for Constructing Divergent Oxepane Frameworks via Cooperative Tertiary Amine/Transition Metal Catalysis

Abstract

We report asymmetric [4 + 3] annulations between isatin-derived Morita–Baylis–Hillman carbonates and two types of vinyl carbonates synergistically catalyzed by tertiary amines and transition metals, through chemoselective assemblies of in situ formed allylic ylides and metal-containing 1,4-dipoles. A range of oxepane frameworks are generally constructed in moderate to good yields with high stereocontrol. Moreover, all four diastereomers for the products bearing vicinal stereocenters are accessible by tuning tertiary amine and metal catalysts.

Construction of Hydrodibenzo[b,d]furan Frameworks from Morita–Baylis–Hillman Carbonates of Isatins and o-Hydroxy Enones via Palladium and Brønsted Base Relay Catalysis

“…In addition, the MBH carbonates from isatins are allylic alcohol derivatives, which are inherently and possibly converted to π-allylmetal species under palladium or iridium catalysis; nevertheless, our recent work demonstrated that they would not be affected by transition metals in the presence of simple allylic carbonates, thus enabling successful cooperative activations of Lewis base and transition metal catalysts (Scheme b) . Although similar phenomena were further observed between the isatin-derived MBH carbonates and other allylic derivatives, here we disclosed that the corresponding π-allylpalladium intermediate III indeed could be generated from the MBH carbonate 1a under Pd(0) catalysis in the absence of other allylic derivatives, rendering the regioselective Tsuji–Trost allylation with suitable nucleophiles, such as o -hydroxybenzylideneacetone 2a . More importantly, the resultant O -allylation intermediate 3a with multiple functionalities could undertake a cascade reaction process under relay Brønsted base catalysis, straightforwardly delivering the complex 1,2,3,4-tetrahydrodibenzo­[ b , d ]­furan architecture 4a incorporating another oxindole pharmacophore motif.…”

Dearomatization of 3-Nitroindoles Enabled Using Palladium-Catalyzed Decarboxylative [4 + 2] Cycloaddition of 2-Alkylidenetrimethylene Carbonates

“…On the basis of our experimental observation and the related literature studies, ,, a plausible mechanism was proposed to illustrate the catalytic cycle (Scheme ). Coordination of a palladium(0) catalyst to 2-alkylidenetrimethylene carbonates 2 or (2-(hydroxymethyl)-3-arylallyl) carbonates 6 gives π-allylpalladium intermediates A-2 or A-6 .…”

“…However, in this aspect, the vast majority of the transformations are confined to the [3 + 2] cycloaddition with diverse π-allyl palladium 1,3-dipoles for the generation of indoline-fused five-membered ring compounds (Scheme a). − In addition, there are only two examples of the [4 + 2] cycloaddition with π-allyl palladium 1,4-[ N , C ]-dipoles for the construction of indoline-fused tetrahydroquinolines via palladium-catalyzed decarboxylation of vinyl benzoxazinanones (Scheme b) . On the other hand, 2-alkylidenetrimethylene carbonates have proved to be a type of π-allyl palladium 1,4-[ O , C ]-dipole precursors, which were used in diverse palladium-catalyzed decarboxylative cycloaddition reactions . However, to the best of our knowledge, the possible involvement of π-allyl palladium 1,4-[ O , C ]-dipoles in the dearomative cycloaddition of electron-deficient heteroarenes has not been exploited.…”

High-order dipolar annulations with metal-containing reactive dipoles

“…Furthermore, Chen and Du proved the generality of a cooperative catalytic strategy in reactions of HODAs with vinyl carbonates (Scheme 16). 52 In the presence of a chiral Pd catalyst and DABCO, vinyl carbonate 74 smoothly reacted with oxindole-derived carbonates 75 to afford spiro-cycloether product 76 in high yields and good enantiocontrols. In the presence of a chiral Ir catalyst and pyridine catalyst, similar medium-sized cyclic products were synthesized from vinyl carbonates 77 and oxindole-derived carbonates 75 .…”