Sequential Gold‐Catalyzed Carbene Transfer/Ring Closure: Oxidative Cyclization of β‐(2‐Alkynylphenyl)‐α,β‐ynones to Indenofuranones

Abstract

b-(2-Alkynylphenyl)-a,b-ynones undergo a gold-catalyzed oxidative two-fold cyclization in the presence of N-oxides to give 1,3-disubstituted-8H-indeno[1,2-c]furan-8-ones in good yields. This cascade process is triggered by a selective oxygen transfer from an N-oxide onto the gold-activated alkynone to generate a a-dioxocarbene intermediate which, via carbene transfer across the remaining alkyne moiety and subsequent cyclization through nucleophilic attack by a carbonyl oxygen, achieves the construction of 1,3disubstituted fused polycyclic furans.

Nitrene Transfer and Carbene Transfer in Gold Catalysis

“…Besides 1,6-carbene transfer followed by 1,2-alkyl or -aryl migration and C−H insertion, such a 1,6-carbene transfer followed by direct cyclization via nucleophilic attack by a carbonyl oxygen was also achieved by the same group in 2018 (Scheme 172). 194 t BuXPhosAuCl (5 mol %) and NaBAr F 4 (7.5 mol %), furnishing the pyranone-fused bridged [3.2.1] skeletons 391 in 40−70% yields with good diasteroselectivities (Scheme 174). 196 On the basis of the control experiments and previous studies on the related donor-/ acceptor-substituted gold carbenes, which possess little tendency for C−H insertion, the authors speculated that it is more likely that the C−H insertion in this case is achieved by the vinyl cation intermediates.…”

“…Besides 1,6-carbene transfer followed by 1,2-alkyl or -aryl migration and C–H insertion, such a 1,6-carbene transfer followed by direct cyclization via nucleophilic attack by a carbonyl oxygen was also achieved by the same group in 2018 (Scheme ). Treatment of β-(2-alkynylphenyl)-α,β-ynones 386 with 5 mol % IPrAuCl/AgNTf as the catalyst and 1.5 equiv of 3,5-dichloropyridine N -oxide as the oxidant in DCE at room temperature could lead to efficient formation of a range of fused polycyclic furans 387 in 60–94% yields. The reaction presumably involves the generation of α-diketo gold carbene species 386-A and carbene/cation intermediates 386-B/386-B′ via 1,6-carbene transfer followed by an intramolecular cyclization, affording the final products 387 .…”

Gold Catalysis and Furans: A Powerful Match for Synthetic Connections

“…In both cases, a final cyclization step affords indenofuran-8-ones 51. 28 Almost at the same time, a related methodology was proposed for the synthesis of furans fused with a heterocyclic ring. 29…”

Synthesis of Heteroarene‐Fused Cyclopentadienes and Related Compounds Suitable for Metallocene Preparation

“…[169] A number of 8H-indeno[1,2-c]furan-8-ones were also obtained in good yields via the catalytic cyclization of β-(2-alkynylphenyl)-α,β-ynones using 3,5dichloropyridine N-oxide as an oxidizing agent; a simple Au(I) phosphine complex and AgNTf 2 were used as the catalytic system (Scheme 39C). [170]…”