Gold‐Catalyzed Cyclizations of cis‐Enediynes: Insights into the Nature of Gold–Aryne Interactions

Abstract

Golden aryne? Gold aryne complexes are inferred as transition states in dual gold‐catalyzed cyclizations of cis‐enediynes (see scheme; DCE=1,2‐dichloroethane). They are better described as ortho‐aurophenyl cations, which react with weak nucleophiles and undergo facile intramolecular insertions into C(sp3)H bonds. Indanes, fused heteroarenes, and phenol derivatives are readily prepared using this method.

New Pathways for the Dual Gold‐Catalyzed Cyclization of Diynes

“…Depending on the connecting tether between the two alkyne moieties, either 5‐ or 6‐ endo cyclization reactions are possible. The activation of diynes based on a benzene backbone, as well as 3,4‐diethynylthiophenes, lead to 5‐ endo cyclization to form gold vinylidenes (Scheme , top), whereas 2,3‐diethynylthiophenes and vinyl‐tethered diynes undergo 6‐ endo cyclization (Scheme , bottom). The 6‐ endo cyclization reaction is also possible in the case of benzene‐tethered diynes when followed by the addition of an external nucleophile ,.…”

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

“…An α‐oxo gold carbene II is then generated through oxygen transfer under selective oxidation of the alkynes by the N ‐oxides. It is worth noting that N ‐oxides do not play the role of base like in the case of the dual activation reactions . Subsequently, the α‐oxo gold carbene II can undergo an intramolecular cyclopropenation to form intermediate III .…”

Au‐ and Pt‐Catalyzed CH Activation/Functionalizations for the Synthesis of Heterocycles

“…Two regioisomeric ortho-auroaryl cation intermediates 96 and 98 were proposed via dual gold-catalyzed 6-endo-dig cyclization model, which can be mutual isomerization via aryne-coordinated gold complex 97. Ortho-aurophenyl cation intermediates 98 could be trapped by a tethered hydroxy or sulfonamide group to deliver the seven-membered O-or N-heterocycles 99 (Scheme 12.45) [48].…”