Gold tandem cyclization

Representative procedure for the gold-catalyzed tandem cyclization/pinacol rarrangement of 3-silyloxy-l,5-enynes. 3a,4,5.6,7,7a-Hexahydro-l-phenyl-3H-indene-3a-carbaldehyde ° ... 

Alkynylaziridines carrying an aryl group have been reported to give spiro [isochroman-4,2 -pyrrolines] with gold salts as catalysts and involve a Friedel-Crafts-type intramolecular reaction followed by cyclization of the aminoaUene intermediate, both initiated by the dual a and n Lewis acidities of gold. Tandem Au(in)-catalysed heterocyclization/Nazarov cyclizations leading to substituted carbocycle fused fiirans have been reported and computational studies support the function of solvent (Scheme 114). ° ... 

Shin has described the gold(I)-catalyzed tandem cyclization/acetoxylation of the tert-butyl carbonate derivatives of l-hexen-5-yn-3-ols to form 4-cydohexene-l,2-diol derivatives [131]. As a representative example, treatment of 90 with a catalytic 1 1 mixture of [P(t-Bu)20-biphenyl] AuCl and AgSbFg led to isolation of cyclohexene 91 in 87% yield as an 8 1 mixture of diastereomers (Eq. (12.49)). 

Krause and Belting studied a tandem catalyzed reaction, in this case intramolecular cyclization and intermolecular hydroalkoxylation. The substrates were various homo-propargylic alcohols in the presence of non-tertiary alcohols and a dual catalyst system consisting of Br( >nsted acids and a gold precatalyst (Equation 8.43). 

An efficient gold-catalyzed tandem protocol for the synthesis of 4-fluo-roisoxazole derivatives 2 has been described from (Z)-2-alkynone O-methyl oximes 1 via cyclization and fluorination.The reactions proceeded smoothly affording compounds 2 with high yields and selectivity (14JOC6444). 

The synthesis of benzo[f ][l,4]diazepines 66 by a tandem hydroamination-cychzation sequence was carried out using a gold(I)-N-hetereocyclic car-bene catalyst (14JOM438). The authors utilized readily available N-alkyl o-phenylenediamines 63 and arylacetylenes 64 as starting materials. They proposed that the reaction proceeds by amination of a gold-activated alkyne with subsequent cyclization of intermediate 65. 

Whereas these transformations require stoichiometric gold compounds, catalytic amounts of both gold and palladium are sufficient for the cycloisomerization of allyl allenoates to allyl-substituted butenolides. Blum and co-workers reported this tandem C-O/C-C bond formation, which is initiated by activation of the distal allenic double bond with PhaPAuOTf (Scheme 4-107). This induces cyclization to an allyl oxonium intermediate, which undergoes deallylation in the presence of Pd2dba3. Nucleophilic attack of the resulting a-vinylgold intermediate at the ti-allylpalladium species and reductive elimination furnish the allylated butenolide and regenerate both catalysts. 

A hydroamination/N-sulfonyliminium cyclization cascade was carried out enantioselectively with gold and BINOL-phosphoric acid catalysts to generate fused indole 188. The method can also be extended to furnish lactams with up to 93% ee (13OL4330). Polycyclic indoline 189 was prepared via an indium/TFA-catalyzed tandem cycloannulation of P-oxodithioesters with tryptamine in yields up to 92% (130L1974). Dixon and colleagues utilized an enantioselective Michael addition/iminium ion cyclization of trypt-amine-derived ureas in the synthesis of tetracyclic indole 190 (22 examples, up to 78% yield and 96% ee) (130L2946). 

So, M., Liu, Y, Ho, C., et al. (2011). Silica-Supported Gold Nanoparticles Catalyzed One-Pot, Tandem Aerobic Oxidative Cyclization Reaction for Nitrogen-Containing Polyheterocyclic Compounds, Chemcatchem, 3, pp. 386-393. 

This reaction was believed to proceed via a tandem sequence consisting of gold-catalyzed C(sp )-H/C(sp)-H cross-coupling/cyclization/oxidative alkynylation. 

Moreover, in a subsequent paper, a reaction based on a gold- or platinum-catalyzed tandem process that involves an intramolecular hydroalkoxylation of a triple bond followed by a Prins-type cyclization has been reported for the synthesis of [3.3.1]bicyclic compounds starting from easily available alkynol derivatives [152] (Scheme 89). 

---