Palladium-catalyzed domino assembly

The palladium-catalyzed domino assembly of norbornene (53), the cw-alkenyl iodide 54, and a terminal alkyne or cyanide reported by Torii, Okumoto et al. [169], provides an... 

The palladium-catalyzed domino assembly of norbornene (65), the ds-alkenyl iodide 66, and a terminal alkyne or cyanide reported by Torii, Okumoto et al. [315] provides an example for a sequence of oxidative addition, intermolecular double bond insertion, and interception of a copper acetylide or potassium cyanide. These reactions with acetylenes have been performed in good yields in the presence of diethylamine, tetra-n-butylammonium chloride, and catalytic amounts of palladium acetate, triphenylphosphine, and copper] I) iodide. Remarkably, they are characterized by complete inversion of the cis configuration of the alkenyl iodide and a high degree of discrimination for the enantiotopic ends of the double bond in norbornene. To account for that, intermediate formation of a cyclopropylcarbinyl-palladium species by a 3-exo-trig cyclization in 67 and subsequent cycloreversion to a new homoallylpalladium intermediate as the direct precursor to 68 and 69 has been assumed. Thus, the products 68 and 69 are formed virtually with complete stereoselectivity (Scheme 8.17). 

As an extension of the Heck reaction, Pd-catalyzed hydroarylation of alkynes and alkenes continnes to attract high level of research interest in simple couphng processes and in cyclization reactions. The use of this type of transformation as part of a domino reaction will be of increasing interest. The research in the field of domino reactions is attracting considerable attention in synthetic organic chemistry since it enables the rapid assembly of complex molecirles in one-pot processes. Very elegant examples of palladium-catalyzed cascade processes where a single catalytic cycle entails several sequential bond transformations have been recently reported [la, b, 2a, b, c]. 

A domino total synthesis of spirotryprostatin B (2) and three of its isomers has been published by Overman and Rosen, who apply two sequential palladium-catalyzed reactions (one-pot) to assemble the two spiro-fused rings [10] (Scheme 3). This work again makes it clear that complex heterocyclic systems may represent a harder challenge to synthetic... 

In essence, these domino-coupling reactions form cyclohexadiene fragments from three two-carbon fragments. The 1 2 coupling of norbomene and iodobenzene discovered by Catellani and Chiusoli can also be adopted to couple norbomene with /3-bro-mostyrene.f hi an attempt to apply this Pd-catalyzed [2+2 + 2] assembly for an alternative and more productive access to Hopf s trifoliaphane, a 1 2 mixture of [2.2]paracyclophan-l-ene and l-bromo[2.2]paracyclophan-l-ene was tfeated with palladium acetate under Jeffery conditions. The main product was the hydrocarbon consisting of three [2.2]paracyclophane units linked by a common bicyclo[3.3.0]octene unit (Scheme Apparently, the key intermediate formed via a palladacycle preferen-... 

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