Norbornene reductive coupling with

Three-component coupling with vinylstannane. norbornene (80). and bro-mobenzene affords the product 91 via oxidative addition, insertion, transme-tallation, and reductive elimination[85]. Asymmetric multipoint control in the formation of 94 and 95 in a ratio of 10 1 was achieved by diastereo-differ-entiative assembly of norbornene (80), the (5 )-(Z)-3-siloxyvinyl iodide 92 and the alkyne 93, showing that the control of four chiralities in 94 is possible by use of the single chirality of the iodide 92. The double bond in 92 should be Z no selectivity was observed with E form[86]. 

One of the first examples of ruthenium-catalyzed C-C bond formation afforded the synthesis of cyclobutenes, from norbornene derivatives with dimethyl acetylenedicarboxylate, and was reported by Mitsudo and coworkers [45, 46] by using various catalysts such as RuH2(CO)[P(p-C6H4F)3]3 or RuH2(PPh3)4. More recently, the complex Cp RuCl(COD) has shown to be an excellent catalyst for the [2+2] cycloaddition of norbornenes with various internal alkynes [45] (Eq. 33) and with a variety of substituted norbornenes and norbornadienes [47]. The ruthenacycle intermediate, formed by oxidative coupling, cannot undergo /1-hydride elimination and leads to cyclobutene via a reductive elimination. 

Chromans and isochromans can be obtained by the reductive Pd-catalysed Heck cyclisation of 4-(2-bromophenoxy)-2-methylbut-l-ene and 3-(2-bromobenzyloxy)-2-methylpropene respectively <07TL2307>. Bromopropyl derivatives of 3,5-dihydroxy-iodobenzene and of 3,5-dihydroxymethyliodobenzene undergo sequential intramolecular alkylations and an intermolecular Heck coupling on treatment with an acrylate under microwave irradiation and Pd-catalysis mediated by norbornene. The products are 5-alkenyl derivatives of pyrano[3,2-g]benzo-2/7-1 -pyrans and pyrano[4,3-/]bcnzo-l77-2-pyrans (Scheme 13) <07JOC775>. 

Domino coupling reactions of aryl halides with norbornene and its derivatives provide a simple route to PAHs. In a four component sequence, norbornene (73) is arylated with an excess of iodobenzene to the terphenyl 74, that can be converted to the benz[e]pyrenes 75 and 76 by classical aromatic conversion reactions [131]. The domino sequence is a consequence of the fact that the five-membered intermediate palladacycle 77 a is able to add a second molecule of iodobenzene (77a —> 77b), and the intermediate arylpalladium halide resulting from reductive elimination in 77 b can even add a third molecule of iodobenzene before the final elimination of the Pd(0) complex PdL2 occurs (see Scheme 38). 

---