Heck-type cyclisation

A standard Heck reaction, as shown in the example below, involves the palladium-catalysed reaction of a halide with an alkene, most commonly an electron-deficient aUcene such as an acrylate, but other types can also be used. Heck-type cyclisation onto olefins is a useful reaction for ring synthesis. 

Intramolecular Heck-type reactions can be used to synthesise indoles,but it is not clear whether the palladium-mediated cyclisations of anilino-acrylates and related sytems operate by this mechanism or via an electrophilic pallada-tion. 

There are also excellent total syntheses of spirotryprostatins which do not apply intermolecular functionalisation of the indole 3-position with a C5 prenyl-type precursor and are, therefore, not discussed in detail. Carreira and co-workers started from 3-diazo-2-oxindole, which was used in a Rh(I)-catalysed cyclopropanation of 1,3-pentadiene. The resulting cyclopropane was subjected to Mgl2-catalysed ring expansion and added to an imine affording the spiro[5.5] partial structure [130, 131]. Overman and Rosen built up the indole system by intramolecular Heck reaction of a functionalised iodoaniline [132,133]. In a model study building up the indole system, Cacchi and co-workers synthesised 3-prenylindoles via Pd-catalysed cyclisation of orf/io-alkynyltrifluoroacetanilides with prenyl esters [134]. 

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