Domino norbornene derivative

RRM processes can also be coupled with an additional CM event Such a scenario is depicted for a norbornene derivative in Scheme 2.18 [12a]. Domino ROM/RCM of 45 with the first-generation Gmbbs catalyst 1 in the presence of terminal olefin 46 yielded the bicyclic enone 47 as a 2 1 mixture of separable ( )- and (Z)-diastereomers. Subsequently, (E -47 was successfully advanced to the cytotoxic macrolactam (-l-)-cylindramide A in a straightforward manner. The enantiopure norbornene 45 was also used in a domino RRM/CM approach to the bicyclo[3.3.0]octene core of the macrolactam geodin A [12b]. 

Norbornene derivatives are common substrates for ring-rearrangement domino processes. Because of their highly strained structure, equilibrium is strongly shifted to the product and, owing to the highly stereocontroUed norbornene synthesis, it is granted easy access to new architectures which otherwise would be diflBcult to synthesize (Scheme 11.18). 

Another unprecedented domino cycloaddition process of a chromium complex, namely a [2+2+l]/[2+l] cycloaddition, was observed by Barluenga and coworkers [316]. These authors treated norbornene 6/4-137 with the Fischer alkynyl Cr car-bene 6/4-138 and obtained, as the main product, not the expected cyclopropane derivative 6/4-139, but compound 6/4-140 (Scheme 6/4.35). 

Formally the reaction combines the ring opening of norbornene, RCM with the terminal double bond and CM with a second alkene. The domino metathesis involving an allylsilyl derivative has been used as a step in the synthesis of (-)-halosaline [69] and (-)-indolizidine [90]. 

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). 

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