Gold-Catalyzed Nitrene Transfer to Activated Alkynes: Formation of α,β-Unsaturated Amidines

Abstract

A gold-catalyzed intermolecular nitrene transfer to alkynes was developed for the first time, revealing a new mode of nitrene transfer and providing a novel access to versatile α-imino metal carbenes. Various mild nitrene-transfer reagents were examined, and iminopyridium ylides especially those based on 3,5-dichloropyridine turned out to be highly effective. With activated alkynes such as N-alkynyloxazolidinones as substrates, α, β-unsaturated amidines were formed in mostly good yields.

Intermolecular and Selective Synthesis of 2,4,5‐Trisubstituted Oxazoles by a Gold‐Catalyzed Formal [3+2] Cycloaddition

“…(1), B-D, Ts = toluene-4-sulfonyl] have very recently been accessed by intermolecular attack of an O-or Nnucleophilic oxidant [4] or nitrene equivalent [5] to an electrophilically activated p system [Eq. The intermediates are quenched by the reaction with a functionality contained within the alkyne starting material (at R or R 1 ), [4,5] a [3 + 3] sigmatropic rearrangement at B, [6] or by further reaction with a nucleophilic oxidant [4c, 7] or nitrile [8] in the absence of faster intramolecular processes. The intermediates are quenched by the reaction with a functionality contained within the alkyne starting material (at R or R 1 ), [4,5] a [3 + 3] sigmatropic rearrangement at B, [6] or by further reaction with a nucleophilic oxidant [4c, 7] or nitrile [8] in the absence of faster intramolecular processes.…”

“…[16] Similarly convergent one-step or one-pot methods to prepare functionalized 1,3oxazoles are rare, [8] and often require the use of highly reactive species with consequent structural limitations. Cationic gold(I) complexes and gold tribromide (Table 1, entries [3][4][5] were similarly effective to [Au-I], though sodium tetrachloroaurate was slightly less active (Table 1, entry 6). Bn = benzyl, brsm = based on recovered starting material, Ms = methanesulfonyl.…”

Synthesis of Cyclobutanones via Gold‐Catalyzed Oxidative Rearrangement of Homopropargylic Ethers

“…[10] Due to the p-acid and electron-donor dual reactivity of gold catalysts, alkynes can be used as precursor of a gold carbenoid, albeit with several exceptions. [11] Leaving group-bearing nucleophiles such as sulfoxide, [12] pyridine/quinoline N-oxide, [13] nitrone, [14] nitro, [15] azide, [16] pyridine N-aminide, [17] sulfur ylide, [18] epoxide [19] and iminopyridium ylide [20] can be used to obtain a carbene intermediate. Many unconventional and efficient transformations to access molecules which are not easily available through traditional organic reactions have been realized.…”

Umpolung Reactivity of Indole through Gold Catalysis

“…Lately we extended this strategy to the use of nitrene precursors as oxidants, providing access to reactive α-imino gold carbenes (Scheme 1A); [9] however, the chemistry has so far been limited to ynamides, [10] which are activated alkynes. In our effort to expand the scope of this type of gold-catalyzed nitrene transfer, [11] we decided to use an azido group as a nitrene precursor, which was inspired by previous studies of gold- [12] and platinum-catalyzed [13] pyrrole synthesis.…”