Switching between the [2π+2σ] and Hetero-[4π+2σ] Cycloaddition Reactivity of Bicyclobutanes with Lewis Acid Catalysts Enables the Synthesis of Spirocycles and Bridged Heterocycles.
Angew Chem Int Ed Engl
; 63(29): e202405222, 2024 Jul 15.
Article
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| MEDLINE
| ID: mdl-38729920
ABSTRACT
The exploration of the complex chemical diversity of bicyclo[n.1.1]alkanes and their use as benzene bioisosteres has garnered significant attention over the past two decades. Regiodivergent syntheses of thiabicyclo[4.1.1]octanes (S-BCOs) and highly substituted bicyclo[2.1.1]hexanes (BCHs) using a Lewis acid-catalyzed formal cycloaddition of bicyclobutanes (BCBs) and 3-benzylideneindoline-2-thione derivatives have been established. The first hetero-(4+3) cycloaddition of BCBs, catalyzed by Zn(OTf)2, was achieved with a broad substrate scope under mild conditions. In contrast, the less electrophilic BCB ester undergoes a Sc(OTf)3-catalyzed [2π+2σ] reaction with 1,1,2-trisubstituted alkenes, yielding BCHs with a spirocyclic quaternary carbon center. Control experiments and preliminary theoretical calculations suggest that the diastereoselective [2π+2σ] product formation may involve a concerted cycloaddition between a zwitterionic intermediate and E-1,1,2-trisubstituted alkenes. Additionally, the hetero-(4+3) cycloaddition may involve a concerted nucleophilic ring-opening mechanism.
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Colección:
01-internacional
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MEDLINE
Idioma:
En
Revista:
Angew Chem Int Ed Engl
Año:
2024
Tipo del documento:
Article
Pais de publicación:
Alemania