Lewis acids, carbophilic

Ferrocen-l,l -diylbismetallacycles are conceptually attractive for the development of bimetal-catalyzed processes for one particular reason the distance between the reactive centers in a coordinated electrophile and a coordinated nucleophile is self-adjustable for specific tasks, because the activation energy for Cp ligand rotation is very low. In 2008, Peters and Jautze reported the application of the bis-palladacycle complex 56a to the enantioselective conjugate addition of a-cyanoacetates to enones (Fig. 31) [74—76] based on the idea that a soft bimetallic complex capable of simultaneously activating both Michael donor and acceptor would not only lead to superior catalytic activity, but also to an enhanced level of stereocontrol due to a highly organized transition state [77]. An a-cyanoacetate should be activated by enolization promoted by coordination of the nitrile moiety to one Pd(II)-center, while the enone should be activated as an electrophile by coordination of the olefinic double bond to the carbophilic Lewis acid [78],... 

Also in the activation of alkynes for nucleophilic attack, gold salts prove to be soft, exceptionally carbophilic Lewis acids, as confirmed by the examples shown in Scheme 3 [10]. According to Utimoto and Fukuda both the addition of water as well as of amines to alkynes are catalyzed by gold(III) salts, in particular by sodium tetrachloroaurate ketones such as 8 and imines such as the ant toxin 10 are obtained as products in excellent yields [10a-e]. In the cyclization reaction giving the 1,4-dioxane 12 developed by Teles et al.,... 

Constructing molecular complexity firom alkynol derivatives A journey firom Fischer carbene complexes to tandem catalysis with gold and other carbophilic Lewis acids 13SL1757. 

Larock developed a powerful approach to isoquinolines which involves copper-catalyzed hydroamination of A -ferf-butyl-2-(l-alkynyl)benzaldimine accompanied by elimination of ferf-butyl group (Eq. 4) [55-59]. Asao and Yamamoto reported a novel synthesis of 1,2,3-trisubstituted isoquinolines through attack of a carbon nucleophile to the carbon-nitrogen double bond of iV-alkyl-2-(l-alky-nyl)benzaldimine and simultaneous hydroamination catalyzed by transition metal [60]. They also achieved isoquinoline synthesis by transition metal-free three-component coupling (Eq. 5) [61]. Takemoto and Yanada reported a related isoquinoline formation by a catalysis of carbophilic Lewis acids such as indium(III), Ni(II), or Au(I)/Ag(I) [62, 63]. Oikawa succeeded in palladium-catalyzed three-component... 

Zhang and coworkers reported two divergent redoxisomerization pathways for yne-enones 151 to afford ring-fused tetrahydroquinolines and tetrahy-droazepines. Product selectivity depends on whether a carbophilic or oxophilic Lewis acid was used. Ring-fused tetrahydroazepines 152 could be obtained in moderate to excellent yields via the carbophihc gold(I)-catalyzed domino reaction under the mild conditions (Scheme 12.66) [70]. 

The activation of alkenes by carbophilic Lewis acids is another way to induce cycloisomerization of dienes through a cation cyclization mechanism, provided that undesirable... 

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