Gold-catalyzed spiro-N,O-ketal synthesis

Abstract

An efficient method for the synthesis of spiro-N,O-ketals with 5- and 6-membered rings was developed via a gold-catalyzed spiroamidoketalization of alkynyl amidoalcohols under mild conditions. This methodology has been successfully applied to the synthesis of a spiro-N,O-ketal analogue of marineosin A.

Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity

“… 134 Alkynyl amidoalcohols undergo a gold(I)-catalyzed spiroamidoketalization giving rise to spiro- N , O -ketals with 5- and 6-membered rings presumably via tandem intramolecular 5- exo -dig hydroamidation/intramolecular oxycyclization. 135 …”

“…Spiro- N,O -ketals with 5- and 6-membered rings have been recently synthesized under mild conditions via gold(I)-catalyzed spiroamidoketalization of alkynyl amidoalcohols. 149 The analogous intramolecular hydroamidation of the corresponding alkynylamide leading to a seven-membered ring was not successful.…”

Asymmetric synthesis of optically active spiroacetals from alkynyl glycols catalyzed by gold complex/Brønsted acid binary system

“…11 More recently, Sarli groups also reported the synthesed of Spiro-N、O-ketals by the using chiral gold(I) complex. 12 Inspired by this finding and the previous work, 5,6 we proposed that the spiroacetals would accessed by cascade intramolecular hydroalkoxylation/ asymmetric At the outset of our study, we investigated a reaction of alkynyl glycols 1a in the presence of 5 mol% PPh 3 AuNTf and 15 mol% of chiral binol-derived phosphoric acid 4a in toluene at room temperature (Table 1, entry 1). To our delight, two different spiroacetal products 2a and 3a were afforded in a total yield of 78% and the ratio of 2:3 was 9:1.…”

An Apparent Umpolung Reactivity of Indole through [Au]‐Catalysed Cyclisation and Lewis‐Acid‐Mediated Allylation

“…Regarding the mechanism,w ith the information available from the control experiments and considering the previous reports, [15] we propose the following tentative mechanism (Scheme 5). The catalytic cycle starts with the formation of the active catalyst[ Au(PPh 3 )OTf] and subsequent 5-endo-dig alkynol cycloisomerisation followed by protodemetallationl eading to the intermediate dihydrofuran B.…”