A Comparative Study of Confining Ligands Derived from Methylated Cyclodextrins in Gold‐Catalyzed Cycloisomerization of 1,6‐Enynes

Abstract

Gold(I) complexes containing monodentate PIII‐ligands built upon methylated α‐cyclodextrins have been synthesized and assessed in the cycloisomerization of 1,6‐enynes, two of the reactions studied involving prochiral substrates. Their performance was compared with that of previously reported mononuclear and dinuclear α‐ and β‐cyclodextrin‐based AuI complexes. Enantiodiscrimination was found to be strongly dependent on the ability of the ligand to position metal‐coordinated substrates inside the cyclodextrin core.

Tetranuclear Dicationic Aurophilic Gold(I) Catalysts in Enyne Cycloisomerization: Cooperativity for a Dramatic Shift in Selectivity

“…With the gold catalyst, various 1,6‐enynes were converted into five‐membered dienes (type I , Figure 1) at rt; this completed the known reactivity of palladium, platinum, and ruthenium, previously identified for such cyclopentenes formation [47–49] . Following this milestone work, mononuclear cationic gold complexes have been shown to promote mostly the formation of either five and/or six‐membered dienes (type I – III , Figure 1), sometimes with a troublesome selectivity [23,50–61] . Au(I) catalytic systems are occasionally able to form bicyclic strained structures such as bicyclo[4.1.0]hept‐4‐enes (type IV , Figure 1) and cyclobutenes (type V – VI , Figure 1).…”

“…[47][48][49] Following this milestone work, mononuclear cationic gold complexes have been shown to promote mostly the formation of either five and/or six-membered dienes (type I-III, Figure 1), sometimes with a troublesome selectivity. [23,[50][51][52][53][54][55][56][57][58][59][60][61] Au(I) catalytic systems are occasionally able to form bicyclic strained structures such as bicyclo[4.1.0]hept-4-enes (type IV, Figure 1) and cyclobutenes (type V-VI, Figure 1). In these cycloisomerization reactions using 1,6-enyne substrates, a high substrate-dependence is observed for the final selectivity.…”

Cavity-shaped ligands for asymmetric metal catalysis

“…These designs have seen a tremendous development over the last decades. Despite these achievements, only one of these assemblies (53) [69] has so far been used as ligand in asymmetric metal catalysis. It consists of a rigid triangular coordination oligomer built from enantiopure 4,4'-bis(alkynyl)-1,1'-binaphthalene units coordinated to cis-(PEt 3 ) 2 Pt corners (Scheme 34).…”

Synthetic Application of Cyclodextrins in Combination with Metal Ions, Complexes, and Metal Particles

“…They collected additional information applying a range of methylated gold complexes ( 88 , Table 25). [166] The highest reactivity was exhibited by benzimidazole‐tagged 88 f (entries 9, 10), whereas most phosphorous‐based catalysts required higher reaction temperature (70 °C vs 25 °C). Complex 88 g provided the highest enantioselectivity (entry 11), but NHC‐capped complexes 88 c and 88 d (entries 3 and 5) also gave reasonably good values.…”