Cyclopropanes intramolecular Heck reaction

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]. 

A ir,o domino-Heck reaction under concomitant rearrangement of the tetracyclic allylcyclopropane endo,exo-bishomobarrelene has been reported 138 the stereoselective reaction proceeds via an intramolecular insertion of a primarily formed carbopallada-tion intermediate into a strained cyclopropane C-C cr-bond (Scheme 96). 

In the above-mentioned Heck-type cascade tetracyclizations, substituents in the acycUc precursors can play a major role and cause the sequential reaction to proceed in an unprecedented direction. A particularly striking example is presented in Schone 39. The acycUc precursors differ from those that undergoe the other type of cascade tetracyclization (see above Scheme 33) only by the propargylic methoxy (silyloxy) group, yet yield—under the typical conditions—an unprecedented tetracyclic system, the structure of which has been proved by X-ray analysis. This cascade reaction may involve an unusual -/ hydride elimination as the last step, or an unprecedented dehydrobromination on an alkylpalladium bromide intermediate to yield a palladiumcarbene species that subsequently undergoes an intramolecular cheletropic addition across the distal double bond to yield the cyclopropane ring. 

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