1,6-Carbene Transfer: Gold-Catalyzed Oxidative Diyne Cyclizations

Abstract

In the presence of a gold catalyst an unprecedented oxidative cyclization of diynes takes place. The reaction cascade is initiated by an oxygen transfer from a N-oxide onto a gold-activated alkyne. The formed α-oxo carbene is transferred across the second alkyne yielding a stabilized vinyl carbene/cation. Alkyl migration or sp(3)-CH insertion then terminates the catalytic cycle by formation of highly substituted functionalized indenones. A 1,6-carbene shift could be supported by the oxidation of the vinyl carbene. This protocol represents an attractive alternative to procedures which are based on the metal-catalyzed decomposition of hazardous, not easily accessible, diazo compounds.

Gold‐Catalyzed Annulations of N‐Propargyl Ynamides with Anthranils with Two Distinct Chemoselectivities

“…Hashmi reported that α‐oxo gold carbenes could react with tethered alkynes to yield alkenyl metal carbenes through a 1,6‐carbene transfer [Scheme , Eq. (1)] . Such a 1,6‐carbene transfer was noted also for rhodium catalysts and for the generation of several gold carbenes that were generated from 1,3‐acyloxy shifts of propargyl acetates .…”

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

“…For the mechanism we suggest the following pathway: oxidation of 1 with the N ‐oxide in the presence of the gold catalyst generates the α,α‐diketo gold carbene II . Then, a cation/carbene intermediate III might be formed through 1,6 carbene transfer …”

“…Recently, a gold‐catalyzed oxidative cyclization of aryl ortho ‐diynes 1 was reported. In the presence of N ‐oxides, a 1,6‐carbene transfer initiated a reaction cascade that delivered functionalized indenones (Scheme a) after the trapping of the final carbene/cation intermediate through a 1,2‐alkyl shift . A related reactivity pattern was observed with aromatic diynes bearing one terminal propargylic acetate as carbene precursor .…”

Gold‐Catalyzed Intermolecular Oxidative Diyne Cyclizations via 1,6‐Carbene Transfer

“…In 2013, we found an unexpected reaction pathway to obtain gold carbene by using N-oxides in diyne systems. [9] N-oxides can be used instead of diazo compounds to access α-oxo gold carbene, too. [3a,d,10] Our group reported on a 1,6-carbene shift of a initially formed α-oxo gold carbene generated by oxygen transfer from N-oxides which was transferred over a tethered alkyne.…”

“…According to our previous work and the work of Zhang, [14,9] a proposed reaction mechanism [15] is shown in Scheme 3. The first step starts with π-activation of COMMUNICATIONS asc.wiley-vch.de the terminal alkyne in the presence of the gold catalysts.…”