Cycloaddition of Diynes with Monoynes

SCHEME 21.8 Co-catalyzed [2+2+2] cycloaddition of diyne with monoyne for synthesis of //-estrone. 

TRANSITION METAL-MEDIATED AROMATIC RING CONSTRUCTION 

SCHEME 21.9 Ru-catalyzed [2-i-2-1-2] cycloaddition of chloro-diyne with monoyne for synthesis of sporolide B. 

SCHEME 21.10 Rh-catalyzed [2-h2-h2] cycloaddition of tosylamide-Unked diynes with alkynes. 

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The chemo- and regioselectivity problems can be solved by the [2+2+2] cycloaddition of diynes with monoynes, although the accessible products are limited to bicyclic compounds. The [2+2+2] cycloaddition of diynes with monoynes has been applied to the synthesis of biologically active molecules and functional materials. The first application in the natural product synthesis was the dl-estrone synthesis using CpCo(CO)j as a catalyst. The [2+2+2] cycloaddition followed by the benzocyclobutane to ort/jo-quinodimethane rearrangement and intramolecular Diels-Alder reaction afforded a dZ-estrone precursor (Scheme 21.8) [11]. 

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