Scheme 12. Three-component reactiono fa-halo-N-tosylhydrazones,indoles and arylboronic acids.Scheme 13. Total synthesis of avrainvilleol.Scheme14. Synthesis of dienes from allenylboronic acids.Scheme 55. ClassicF ischer indole reaction with N-tosylhydrazones.Scheme56. Synthesis of 1H-indazoles via ab enzyne intermediate.Scheme57. Proposed mechanism for the synthesis of 1H-indazoles.
A domino process that converges the migratory insertion of carbene with a Heck reaction has been established as a versatile tool for the synthesis of 2-arylidene-3-aryl-1-indanones from very stable and easily accessible N-tosylhydrazones and 2'-iodochalcones. The reaction selectively proceeds through 5-exo-trig cyclization and delivers the products selectively with the E configuration of the double bond in excellent yields. The one-pot synthesis of 2-arylidene-3-aryl-1-indanones involving in situ synthesis of both 2'-iodochalcones and N-tosylhydrazones has also been demonstrated.
Transition metal free Brønsted acid mediated synthesis of biologically important pyrido[1,2-a]indole scaffolds through aza-Nazarov type cyclization of readily available diaryl(2-pyridyl)methanol using formic acid has been developed. This methodology has been successfully extended to synthesize atropisomers.
An efficient diastereoselective synthesis of α-tetralone-fused spirooxindoles is reported. The Pd-catalyzed domino reaction proceeds through a carbene migratory insertion followed by a 6-endo-trig mode of conjugate addition sequence from easily accessible isatin-derived N-tosylhydrazones and 2'-iodochalcones. The versatility of the protocol has been showcased by high functional group tolerance, broad substrate scope, and extension to an expedient synthesis of spiroacenaphthylenes. NMR reaction profiling and deuterium-labeling investigations provide insight into the mechanistic pathway.
The carbene migratory insertion involving a domino reaction by highly stable, reusable, and binaphthyl-stabilized Pd-nanoparticles (Pd-BNP) is disclosed. The reaction was catalyzed by 2 mol % of a heterogeneous Pd-BNP catalyst under external ligand-free conditions, and it afforded 3-aryl-substituted indanone derivatives in up to a 90% yield with exclusive E-selectivity. Furthermore, a one-pot reaction and derivatization of indanone derivatives were also successfully demonstrated.
A transition-metal-free and base-mediated carbene insertion across sulfur-sulfur and selenium-selenium bonds has been developed by employing N-tosylhydrazone as a stable and safe carbene precursor. The ylide formation from carbene followed by Stevens rearrangement are considered to be the key steps. This thiol and selenolfree protocol delivers thioacetals and selenoacetals in good to excellent yields in short reaction time with good functional group tolerance. A one-pot synthesis involving in situ generation of tosylhydrazone has also been demonstrated.
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