Cyclization of η³-Benzylpalladium Intermediates Derived from Carbene Insertion

Abstract

Migratory insertion of benzylidene carbene ligands into arylpalladium(II) species generates η(3)-benzylpalladium intermediates that can cyclize to generate five- and six-membered rings with new sp(3) centers. The reaction tolerates a range of arene functional groups and stabilized enolates. The products generated through this reaction are 1-arylindanes and 1-aryltetralins that are common to a range of natural products.

Transition-Metal-Catalyzed Cross-Coupling with Ketones or Aldehydes via N-Tosylhydrazones

“…Mechanistically, a migratory insertion of α,β-unsaturated carbene generates an allylic palladium species, which undergoes an intramolecular substitution with the tethered carbon nucleo­phile (Scheme a). Later, Van Vranken and co-workers disclosed that simple aryl aldehyde derived N -tosyl­hydrazone can also participate in such kind of transformation, in which an η 3 -benzyl palladium species is involved in the substitution process . Both indane and tetraline derivatives can be synthesized using this transformation, in which a 5-exo-trig or 6-exo-trig cyclization is involved in the formation of the second C–C bond, respectively (Scheme b).…”

“…Later, Van Vranken and co-workers disclosed that simple aryl aldehyde derived N-tosylhydrazone can also participate in such kind of transformation, in which an η 3 -benzyl palladium species is involved in the substitution process. 103 Both indane and tetraline derivatives can be synthesized using this transformation, in which a 5-exo-trig or 6-exo-trig cyclization is involved in the formation of the second C−C bond, respectively (Scheme 25b). When the substitution occurs at the other side of the allylic moiety, two C−C bonds can be constructed, but not on the same carbon.…”

Production of Csp3–Csp3 Bonds through Palladium‐Catalyzed Tsuji–Trost‐Type Reactions of (Hetero)Benzylic Substrates

“…[47] This one-pot reaction oc- curred even with a highly hindered benzylidene group [Equation (57)] but the cyclization step did not proceed with a butylidene instead of a benzylidene group [Equation (59)]. This difference indicates that the η 3 -benzylpalladium unit is formed from the terminal aryl group and not from the internal aryl moiety, as depicted in Scheme 12.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…A mechanistically similar process was involved in the synthesis of indanes using palladium/base catalyzed coupling of iodobenzene-malonates and tosylhydrazones [1153]. Other processes emanating from tosylhydrazones that likely involve carbene complex intermediates include: (1) arylative dearomatization of furancarboxaldehyde tosylhydrazones containing pendant alcohol groups [1154]; (2) N-vinylation of indoles and carbazoles through palladium catalyzed coupling of the N-H compounds with diazo compounds [1155]; (3) a DFT study of palladium-catalyzed preparation of 1,2,4-trienes from propargylic carboxylates and tosylhydrazones [1156]; and (4) enantioselective intramolecular C-H insertions using hydrazone-derived copper carbenoids [1157].…”