Gold carbenoids cyclization

The solvent effect on the regioselectivity of the AuCls-catalyzed cycloisomerization of a bromoallenyl ketone was evaluated by density functional theory calculations. Upon the generation of the gold carbenoid intermediate from cyclization of the aUene precursor, the tetrahydrofiiran solvent can act as a proton shuttle to assist the 1,2-H migration to afford the 2-bromofuran product (14S2149). 

A gold-catalysed transformation of a-(2-indolyl) propargylic alcohols with imines in the presence of the oxidant 8-isopropylquinoline A-oxide gives dihydro-y-carbolines by intermolecular trapping of an a-carbonyl gold carbenoid intermediate, followed by cyclization and a gold-assisted 1,2-acyl migration (Scheme 129). ... 

Yeom et al. demonstrated that the gold-catalyzed redox cyclization reaction of (Z)-isomer of o-alkynylaryl ketoximes (Z)-95 produced isoindole 96 (Scheme 27.34) [43]. The reaction proceeds through N—O bond redox reaction to form gold carbenoid intermediate 98 and subsequent cyclization and elimination of the gold catalyst, furnishing the isoindole 96. In contrast, reaction of the -isomer (E)-95 afforded isoqunoline oxide 100 [44],... 

In gold catalyzed transformations, the carbenoid intermediates such as 31 arising from a 5-exo-dig cyclization can also be either oxidized in the presence of Ph2SO leading to carbaldehyde 32 or trapped by an alkene to give bis-cyclopropanic derivatives 33 (Scheme 5.12) [55-57]. 

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