Methods for the Synthesis of Functionalized Pentacarboxycyclopentadienes

Abstract

Protocols for the synthesis of diverse PCCPs are described. Starting from readily available pentacarbomethoxycyclopentadiene, transesterification offers single-step access to aliphatic ester derivatives, while treatment with amines produces mono- or diamides. For less nucleophilic alcohols, an alternative procedure involving the in situ generation and esterification of a putative cyclopentadiene penta-acid chloride has been developed.

Synthetic Routes towards Multifunctional Cyclopentadienes

“…These were recently found to be very efficient Bronsted acid catalysts when derivatized with chiral substituents . In a subsequent report, Lambert and co‐workers described the preparation of a series of differently substituted PCCPs (Scheme B), expanding the scope of their original work significantly …”

“…[42] In as ubsequentr eport, Lambert andc o-workersd escribed the preparation of as eries of differently substituted PCCPs (Scheme 11 B), expanding the scope of their originalwork significantly. [43] An interestingp rospectt hat the anionic Cps open up is their potentials olubility in water.B eing able to preparep olysubstituted and water-soluble Cps and metal complexes would be desirable from agreen-chemistry point of view.Additionally, for some groups it is also favorable for the preparation of 99m Tc complexes,w hichf requently feature Cp-ligands and all reactions need to be conducted in water because the product is directly used for radioimaging in patients. For this application, the water soluble 1,2-and 1,3-substituted sodium cyclopentadienyl ligands (64 and 65)r eported by Sabatino andc o-workers are of great interest (Scheme 12).…”

Chiral Pentacarboxycyclopentadiene-Based Brønsted Acid-Catalyzed Enantioselective Desymmetrization of Meso-Epoxides by 2-Mercaptobenzothiazoles

“…The PCCP catalysts 1 and 2 were prepared according to the reported literature procedures. 20 Pentacarbomethoxycyclopentadiene (307 mg, 0.86 mmol), (1 R ,2 S ,5 R )-(−)-8-phenylmenthol (2.00 g, 8.61 mmol, 97%), and N -methylimidazole (0.412 mL, 5.16 mmol) were dissolved in 8.6 mL of toluene (0.1 M) in a two-neck flask. A steady flow of dry N 2 was allowed for the removal of methanol.…”

Synthesis of 1,2,3,4,5‐Penta(methoxycarbonyl)cyclopentadienides through Electrocyclic Ring Closure and Ring Contraction Reactions

“…Much attention was paid to penta(methoxycarbonyl)cyclopentadienyl potassium 1a (PMCP) within the chemistry of metallocenes, since its first discovery by Diels . Recently, Lambert et al developed a novel highly efficient type of chiral Brønsted acid catalyst, which is easily derived from PMCP. Although the new platform first showed efficiency for specific examples of Mukaiyama–Mannich and oxocarbenium aldol reactions (the substrates must have a 2‐hydroxyphenyl substituent for good association with it) it was later extended to asymmetric Diels–Alder cycloaddition reactions and synthesis of chiral cyclic aminals .…”