Alkene‐Directed N‐Attack Chemoselectivity in the Gold‐Catalyzed [2+2+1]‐Annulations of 1,6‐Enynes with N‐Hydroxyanilines

Abstract

Kinetically unstable nitrones are generated from gold-catalyzed reactions of 1,6-enynes with N-hydroxyanilines, and subsequently trapped by tethered alkenes to furnish [2+2+1]-annulations. Our experimental data reveal that such nitrones arise from atypical N-attack chemoselectivity that is triggered by tethered alkenes to facilitate the key protodeauration reaction.

Development and Application of a Sensor Based on Carbonaceous Materials and Cobalt Phthalocyanine Composite for Electrochemical Determination of Uric Acid

“…In the preceding reactions (Scheme ), the N‐attack of N ‐hydroxyanilines at terminal arylalkynes generally afforded hydration products because the corresponding ketone‐like nitrone intermediates are generally unstable and easily hydrolyzed;41,43 only aldehyde‐derived nitrones are applicable in dipolar [3+2] cycloadditions with alkenes. Nevertheless, in the case of 1,6‐enynes, their gold‐catalyzed reactions with N ‐hydroxyanilines enable [2+2+1]‐annulations with N ‐hydroxyanilines;44 P( t‐ Bu) 2 ( o ‐biphenyl)AuNTf 2 proved to an efficient catalyst (Scheme ). The scope is broad and applicable to not only acyclic O‐ and N‐linked enynes but also to alkene‐ and benzene‐bridged analogues.…”

Gold‐catalyzed Intermolecular Oxidations of 2‐Ketonyl‐1‐ethynyl Benzenes with N‐Hydoxyanilines to Yield 2‐Aminoindenones via Gold Carbene Intermediates

“…We prepared the alkenylketone substrates 5 l – n , which afforded the desired products 6 l – n in 62–90 % yields (entries 12–14). Herein the byproduct 7 l was obtained in a minor proportion (20 %) because of a N‐attack of the hydroxyaniline on 5 l (entry 12) . An electron‐rich heteroaryl group avoids this byproduct because the oxomium intermediate III forms rapidly [Eq.…”

Berichtigung: Alkene‐Directed N‐Attack Chemoselectivity in the Gold‐Catalyzed [2+2+1]‐Annulations of 1,6‐Enynes with N‐Hydroxyanilines

“…Alkoxy-derived 1,6-enynes 7d and 7e yielded 8d and 8e,8e' ' (entries 4, 5). [7] Theenhanced yields (78-85 %) of resulting 8d and 8e relative to that of their unsubstituted analogue 8a reflected the Ingold-Thorpe effect. [8] X-ray diffraction of annulations were applicable to cycloalkenebridged 1,6-enynes 7fand 7g,yielding the expected products 8fand 8gin 54 %and 89 %yields,respectively.The data from Tables 2and 4clearly indicate that 1,6-enynes 1h, 1i, 7c,and 7f bearing electron-rich alkenes are less efficient substrates; this reaction trend matches well with the well-known cycloadditions between nitrones and alkenes.…”

“…This stereochemistry is in accordance with starting transconfigured 1,6-enyne 1a.T he molecular framework of compound 3a was confirmed by X-ray diffraction of its NTsbridged analogue 3c (Table 2, entry 2). [7] Table 2assesses the scope of the annulation reactions with various acyclic O-a nd N-linked 1,6-enynes 1b-1e bearing various mono-and 1,2-disubstituted alkenes,yielding bicyclic products 3b-3e in 72-92 %yields (entries 1-4), together with hydration product 1b-H and indole species 4c in am inor proportion (13-17 %). X-ray diffraction of the 3c cycloadduct confirmed the molecular structure with the nitrogen linked to the CMe carbon and the oxygen linked to the CPh carbon.…”

“…X-ray diffraction of the 3c cycloadduct confirmed the molecular structure with the nitrogen linked to the CMe carbon and the oxygen linked to the CPh carbon. [7] We prepared C(3)-phenyl substituted 1,6-enynes 1fand 1g to test the stereocontrol of the reaction. Gratifyingly,t heir resulting products 3f and 3g were obtained with single diastereomers (d.r.…”