Pt-Catalyzed Enantioselective Cycloisomerization for the Synthesis of Planar-Chiral Ferrocene Derivatives

Abstract

Enantioselective cycloisomerization of 2-ethynyl-1-ferrocenylbenzene derivatives proceeded by using a chiral cationic platinum catalyst at room temperature. The intramolecular reaction gave planar-chiral naphthalene- and anthracene-fused ferrocene derivatives with high to excellent ee.

Simultaneous construction of axial and planar chirality by gold/TY-Phos-catalyzed asymmetric hydroarylation

“…However, to the best of our knowledge, simultaneous construction of multiple chiralities by asymmetric gold catalysis has not been reported so far, this hypothesis faced considerable challenges: (1) the universal and efficient asymmetric intramolecular desymmetric cyclization for the construction of planar ferrocene derivatives was not well developed (In the work of refs. 11 , 12 , 10–20 mol% catalytic loading was used), (2) on the other hand, simultaneous construction of axial and planar chiral molecules via asymmetric catalysis has rarely been reported 52 , 53 and innate reluctance to undergo a related asymmetric desymmetric aromatization, and (3) the inherent difficulties to asymmetric gold catalysis, which stem from its linear coordination geometry and the outer-sphere nature of Au(I)-catalysis 44 – 50 . To test our hypothesis, our investigation began with the cyclization of ortho-alkynylaryl ferrocene derivative 1aa .…”

“…S3 ). Unfortunately, catalysts used by Urbano-Carreño 11 , Shibata 12 , or Uemura 10 all failed to give the desired cyclization product (Fig. 2 , entries 1–3).…”

“…1a ). Later, Shibata et al 12 reported the similar reaction enabled by a Pt-catalysis. Meanwhile, the capacity of intramolecular hydroarylation is impressively complemented by various other versatile stereocontrolled methodologies.…”

Asymmetric C–H Bond Functionalization of Ferrocenes: New Opportunities and Challenges

“…This process is the first example that planar chirality is constructed by using gold catalysis. Soon after this work, Shibata and coworkers developed a similar reaction to synthesize planar chiral ferrocenes, utilizing Pt/(S, S)-Ph-BPE as the catalytic system (Figure 5B) [92]. Simultaneously, a plausible catalytic cycle was proposed.…”

Stereoselective arene formation

“…Similar naphthalene and anthracene-merged ferrocene products were obtained by a related desymmetrising aromatization method reported by Shibata (Scheme 14). 32 In a cationic Pt-catalyzed cycloisomerisation using a chiral BPE ligand, excellent yields and enantioselectivities were achieved. Preliminary mechanistic studies suggest activation of the alkyne moiety followed by an arene-forming 6-endo-dig cyclisation giving the fully aromatic planar chiral ferrocenes.…”