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

Abstract

A cascade assembly between isatin-derived Morita−Baylis−Hillman carbonates and o-hydroxybenzylideneacetones has been developed under the relay catalysis of Pd(PPh 3 ) 4 and DBU, affording a spectrum of 1,2,3,4-tetrahydrodibenzo[b,d]furan architectures incorporating a spirooxindole motif in moderate to good yields with excellent diastereoselectivity. The fused indole analogues were similarly furnished by employing the benzylideneacetones having an o-TsNH group.Letter pubs.acs.org/OrgLett

An Access to Highly Functionalized Dihydrobenzofuran Spirooxindole Scaffolds

“…For explaining the formation of the polycyclic compounds, a plausible reaction mechanism was proposed on the bases of the present results and the previous works (Scheme ). First, ortho -hydroxychalcone 1 was deprotonated by base to give a phenolate ( A ).…”

Expeditious entry into carbocyclic and heterocyclic spirooxindoles

“…A domino reaction between isatin-derived Morita–Baylis–Hillman carbonates 132 and ortho -hydroxy enones 133 would furnish 1,2,3,4-tetrahydrodibenzo[ b,d ]furan incorporating spirooxindole 134 using a relay catalyst combining Pd(PPh 3 ) 4 and DBU (Scheme 79a). 66 o -Hydroxycinnamaldehyde 133a under the same reaction conditions yields a pair of diastereoisomers 134b and 134c (Scheme 79b). Moreover, on treating 133b with benzylideneacetone, 135 with an o -TsNH group forms 2,3-disubstituted indole 136 which can be further treated with a catalytic amount of DBU at high temperature furnishing indole-fused analogs 137 (Scheme 79c).…”

Convenient Synthetic Protocols for Diverse Functionalized Dihydrobenzofuran-Fused Spiro-indanedione-oxindole Scaffolds

“…For this purpose, some elegant synthetic protocols have been developed in the past years for the construction of spiro-indanone-oxindole systems . Recently, the multifunctional Morita–Baylis–Hillman (MBH) carbonates of isatins have been recognized as powerful synthons in many transformation and annulation reactions, which could be employed for convenient synthesis of various functionalized spirooxindoles. , In this respect, MBH carbonates of isatins have been also employed to construct mixed spiro-indanone-oxindole motifs . For example, Ouyang and Chen first developed a chiral catalyst-controlled switchable chemo- and diastereodivergent annulation reaction of MBH carbonates of isatins and 2-arylidene-1,3-indanediones for enantioselective construction of polycyclic spiro-indanone-oxindoles (eq 1 in Scheme ).…”