Benz-annulation reaction

The benzannulation reaction with small alkynes such as 1-pentyne may generate a two-alkyne annulation product. In this case the original [3+2+l]-benz-annulation is changed to a [2+2+1+1]-benzannulation. After CO dissociation and insertion of the first alkyne, the coordinated a,/J-unsaturated moiety in the vinylcarbene complex is supposed to be replaced by the second alkyne. The subsequent reaction steps give the phenol 112 (Scheme 50). 

Brominated boronic acid 179 also served as a reagent for cross-coupling/direct arylation cascade annulation. The palladium-catalyzed reaction of 179 with 1,4-dibromonaphthalene (180) provided doubly annulated product 181 in 51% yield along with monoannulated and debrominated product 175 in 35% yield (Scheme 22.42) [65b]. Use of 1,8-dibromophenanthrene (182) as the coupling partner resulted in the production of a 1 1 mixture of benz[c]indeno[l,2,3-/tijacephenanthrylene (183) and benz[e]acephenanthrylene (184). 

---