Gold- and Copper-Catalyzed Cycloisomerizations towards the Synthesis of Thujopsanone-Like Compounds

In the search for a new access to thujopsanone related compounds by cycloisomerization reactions of unsaturated propargylic alcohols and acetates, we found several interesting reaction types and demonstrated the complementarity of Au, Pt, and Cu catalysts. Thus, 6-en-1-yn-3-ol 10 a underwent clean cyclization/ether formation to 16, in particular using Au catalysts (76-98%) or a newly prepared Cu-I-triflimidate-catalyst (94%). The corresponding acetate 11 a underwent either the cycloisomerization with concomitant [1,2]-acyl shift (to 12: 78% using AuCl3) or an unprecedented rearrangement-cycloaddition leading to 20 (43% using [(tBuXPhos)AuNTf2]), a strained fused tricyclic ring system containing a [2.2.0] bicyclic subunit.