Palladium‐Catalyzed Tandem Reaction of Alkyne‐Based Aryl Iodides and Salicyl N‐Tosylhydrazones to Construct the Spiro[benzofuran‐3,2′‐chromene] Skeleton

Abstract

Ac onvenientp alladium-catalyzed tandem reactiono fa ryl iodides and salicyl N-tosylhydrazones has been achieved to afford as eries of compoundsc ontainingt he novels piro[benzofuran-3,2'-chromene] scaffold in moderate to good yields. This efficientc atalytic reaction, which tolerates various functional groups,c ombines alkyne-based 5exo-dig cyclization, palladium(II)c arbenem igratory insertion and intramolecular cyclization, generating three new bonds in one reaction.

Accessing Medicinally Relevant O‐Benzofused Heterocycles through C−X Activation: Recent Trends

“…[37] Lui's group disclosed a novel ligand-free approach to prepare spiro[benzofuran-3,2'-chromene] structures in a one-pot manner using 5 mol % Pd(PPh 3 ) 4 and K 2 CO 3 as a base (Scheme 12). [38] Arylhalide substrates and salicyl N-tosyl-hydrazone derivatives were employed as suitable precursors for this transformation leading to the desired structures in high yields. The reaction showed broad tolerance for various functional groups, particularly for electron rich substituents in the para position relative to the hydroxy group on the N-tosylhydrazone precursores.…”

Recent Advances in Transition‐Metal‐Catalyzed Reactions of N‐Tosylhydrazones

“…The first access to the novel spiro[benzofuran-3,2'chromene] scaffold by a palladium-catalyzed tandem reaction involving N-tosylhydrazones was published by the group of Liu in 2016 (Scheme 72). [97] The reaction of alkyne-based aryl iodides with salicylic Ntosylhydrazones proceeded via a sequence of alkynylbased 5-exo-dig cyclization, palladium(II) carbene To emphasize the potential of sequential intra-or intermolecular bond formations before the final βhydride elimination step, a regioselective synthesis of naphtho-fused heterocycles was realized by the group of Langer (Scheme 74). [98] The reaction proceeds through a palladium-catalyzed tandem reaction of Ntosylhydrazones, derived from ketones, with dibromide compounds.…”

“…The first access to the novel spiro[benzofuran‐3,2’‐chromene] scaffold by a palladium‐catalyzed tandem reaction involving N ‐tosylhydrazones was published by the group of Liu in 2016 (Scheme 72). [97] The reaction of alkyne‐based aryl iodides with salicylic N ‐tosylhydrazones proceeded via a sequence of alkynyl‐based 5‐ exo‐dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization to form three new bonds in one step. Moreover, the group further studied the application of N ‐tosylhydrazones in the synthesis of related spiro compounds.…”

Dictating the Reactivity of η3-Oxoallyl Pd-Intermediate toward 5-exo-trig Cyclization: Access to Indano-spirooxindoles

“…N -Tosylhydrazone, a nucleophilic coupling partner, was well-appreciated as carbene precursor in various transition-metal-catalyzed reactions owing to their in situ origin of unstable diazo compounds. − Quite a lot of reactions have been combined with the carbene migratory insertions in a pre- or postmanner to set a novel tactic in modern organic synthesis . For instance, carbonylation, carbopalladation, Sonogashira reaction, and capture by C-, N-, and O-nucleophiles − were successfully merged in a domino fashion. Further, our recent study toward uniting the carbene process with Heck-type cyclization and conjugated addition uncovered some novel transformations wherein the reaction of iodochalcone with aryl tosylhydrazone afforded the 3-aryl-1-indanone derivatives by 5- exo-trig cyclization of η 3 -benzyl-Pd intermediate .…”