Catalytic Intramolecular Cyclization of Alkynyl Cyclic Acetals via Chemoselective Activation Leading to a Phenanthrene Core

Abstract

An intramolecular cyclization reaction of alkynyl cyclic acetals to synthesize various phenanthrene derivatives in the presence of silver triflate (AgOTf) or boron trifluoride etherate (BF3·OEt2) as catalysts has been developed. By using AgOTf or BF3·OEt2 appropriately depending on the substituents various alkynyl cyclic acetals were converted to the corresponding phenanthrene derivatives. Investigations of reaction mechanisms, X-ray structure of the product, and computational density functional theory (DFT) study suggested that the reaction proceeds via alkyne activation (π-activation) or acetal activation (σ-activation) pathways based on π- or σ-Lewis acidities.

Advances in gold catalyzed synthesis of quinoid heteroaryls

“…XPhosAu(CH 3 CN)NTf 2 exhibited lower reactivity at room temperature (50% conversion), requiring 80 °C to achieve comparable reactivity (58% yield of 2h ) with byproduct contamination. Drawing from prior studies and relevant literature sources, 90–92 a plausible mechanism is proposed in Scheme 7. Initially, 6- endo -dig cyclization of the gold-activated alkyne group with the tethered azide moiety produces the adduct A , which then yields the crucial α-imino gold carbene species B upon N 2 extrusion.…”

Gold‐Catalyzed Synthesis of Ortho‐Quinone Methide Analogues as Reactive Synthetic Precursors

“…[18] We previously developed a gold(I)-catalyzed intermolecular cyclization of 2-alkynyl cyclic acetals to synthesize various fused cyclic compounds via alkyne activation. [19] The gold-catalyzed intramolecular cyclization of 2-(2-amino)phenyl-2-substituted alkynyl ketone (α,β-ynone) derivatives proceeded selectively, affording six-membered rings via 6-endo-dig cyclization (Scheme 1, Related Reaction); [20] however, this reaction is limited to disubstituted alkynes. In addition, the 5-exo-dig cyclization would be less favorable for generating thermodynamically unstable exomethylene structures compared with the 6-endo-dig cyclized quinolone nucleus.…”