Ni-Catalyzed 1,5-Sigmatropic Ester Shift on Cyclopentadiene Rings: Regioselective Conversion of 5,5-Disubstituted Cyclopentadienes to CH₂–Cyclopentadienes

Abstract

Described herein is a nickel(II)-catalyzed regioselective rearrangement of 5,5-disubstituted cyclopentadienes to fully functionalized CH 2 −cyclopentadienes via successive 1,5-sigmatropic shifts of the ester group on the quaternary carbon and hydrogen under mild basic conditions. The obtained CH 2 −cyclopentadienes were also readily applied in the preparation of highly functionalized dibenzo-[e,g]azulene derivatives in two steps.

Cobalt-Catalyzed (3 + 2) Cycloaddition of Cyclopropene-Tethered Alkynes: Versatile Access to Bicyclic Cyclopentadienyl Systems and Their CpM Complexes

“…Finally, we also tested the cycloaddition of precursors equipped with two substituents at the cyclopropene sp 3 carbon (R ″ ≠ H, Scheme ). A substrate bearing a phenyl and a carboxylic ester at this center led to a cyclopentadienyl adduct, 2zb‴ , in which the carboxy ester experienced a formal 1,3-shift. , On the other hand, a precursor bearing two methyl groups at the CPE (R″ and E = Me) led to the expected bicyclic adduct 2zc″ (26% yield), together with a formal dehydro Diels–Alder product ( 4zc , 52% yield) …”

Temperature-Dependent Divergent Cyclopentadiene Synthesis through Cobalt-Catalyzed C–C Activation of Cyclopropenes

“…Since the methylene group in cyclopentadienes is important for further manipulation and application, it is highly valuable if 1,2,3,4-tetrasubstituted cyclopentadienes with methylene can be efficiently prepared by this ring expansion strategy. During the preparation of the manuscript, a nickel-catalyzed 1,5-ester shift reaction of 5,5-disubstituted cyclopentadienes to prepare methylene-containing cyclopentadienes was reported by the Wang group . Inspired by the putative 1,5-sigmatropic ester shift observed from the reaction of 1c and 2a ( vide supra ), we systematically optimized the reaction conditions to improve the efficiency (Table ; for details, see SI).…”