Gold- and Iodine-Mediated Internal Oxygen Transfer of Nitrone- and Sulfoxide-Functionalized Alkynes

Abstract

Intramolecular oxygen transfer of nitrone– and sulfoxide–alkynes was achieved using a catalytic amount of Au(I) and a stoichiometric amount of iodine. The Au(I)-catalyzed cyclization of a nitrone–terminal alkyne afforded a cyclic iminoester, while cyclization of analogous nitrone–internal alkynes yielded aldehyde–enones. The I2-mediated cyclization of nitrone–alkynes afforded iodinated γ-lactams and the I2-mediated internal redox of the closely related sulfoxide–alkynes gave diketones functionalized with a thoiether.

Recent Developments in the Cyclization of Alkynes and Nitrogen Compounds for the Synthesis of Indole Derivatives

“…[234] Iodo-induced cyclization of ortho-alkynylnitrones gave iodinated isoindolinones 162 via a formal 1,2oxygen transfer from the NÀ O bond to the nitrone carbon (Table 6, entry 4). [235] A remarkable competition between 5-exo, 6-endo and 6-exo-dig cyclization was carried out in the anionic cyclization of ortho-alkynyl hydrazides. In these studies, the paths were influenced by the external factors and the substituents at the alkyne, whereas isoindoline derivatives 163 were formed when aryl groups are directly bonded to the alkyne (Table 6, entry 5).…”

Gold-Catalyzed Complementary Nitroalkyne Internal Redox Process: A DFT Study

“…An interesting class of gold-catalyzed reactions that needs a mention in this context are the catalytic internal redox cyclisation's (Xiao and Li, 2011;Zhang, 2014;Yeom and Shin, 2014). The oxygen atom transfer to alkynes catalyzed by gold complexes is a well-known addition−elimination process employing nucleophilic oxygen atom donors such as nitro (Asao et al, 2003;Li et al, 2005;Ramana et al, 2010), amine-/pyridine N-oxides (Cui et al, 2009;Nosel et al, 2013), nitrone (Heom et al, 2008;Pati and Liu, 2009;Chen et al, 2011), sulfoxides (Shapiro and Toste, 2007;Lu et al, 2013), and epoxides (Hashmi et al, 2008;Lin et al, 2008), reacting with the activated alkynes.…”

The Outer‐Sphere Mechanism of Nitrene Transfer onto Gold(I) Alkyne Complexes

“…[13][14][15][16][17] It is well known that a-oxo metal carbene/carbenoids are powerful intermediates in organict ransformationss uch as CÀHa ctivation, ylide formation,a nd cyclopropanation reactions. [18,19] However,aclassic approacht ot hese compounds involves diazo carbonyl compounds,w hich requirec omplicated manipulation.S ignificant efforth as therefore been directed toward the development of novel and safer synthetic methods to generate, for instance, a-oxo gold carbenes by using oxidant reagents that promote intra- [20][21][22][23] or intermolecular [24,25] oxygen transfer to alkynes, which thus avoids the undesired diazo compounds. [26][27][28] Access to difficult-to-obtain and synthetically versatile aimino carbenes was recently realized by using an approach that mimics that of oxo derivatives.…”

“…However, a classic approach to these compounds involves diazo carbonyl compounds, which require complicated manipulation. Significant effort has therefore been directed toward the development of novel and safer synthetic methods to generate, for instance, α‐oxo gold carbenes by using oxidant reagents that promote intra‐ or intermolecular oxygen transfer to alkynes, which thus avoids the undesired diazo compounds …”