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

Abstract

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 10a 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 AuCl(3)) or an unprecedented rearrangement-cycloaddition leading to 20 (43% using [(tBuXPhos)AuNTf(2)]), a strained fused tricyclic ring system containing a [2.2.0] bicyclic subunit.

Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

“…Gold-catalyzed isomerization has been also employed in the search of an appropriate route to (−)-thujopsanone, a derivative of the natural terpene (−)-thujopsene, widely employed in cosmetics [ 16 ]. Although the first aim of the authors remained unachieved, and the obtained compound 9 did not exhibit the appreciated properties of the initial target [ 17 ], the chemistry developed merits further consideration ( Scheme 4 ) [ 18 ]. Thus, it was observed that enynol 10 provided the unexpected ether 11 in the presence of different gold catalysts, in amounts similar to those produced by some other metal salts such as copper or platinum complexes.…”

Natural sesquiterpenoids

“…123 Total syntheses of the racemic sesquiterpenes 144, 145 and majusculone 146 have been reported. 125 9 Carotane, acorane, cedrane, zizaane and prezizaane 84 A goldand copper-catalyzed cycloisomerization has been used in the synthesis of thujopsane-like compounds.…”

Enantioselective Cycloisomerization of 1,5‐Enynes Promoted by Cyclometalated NHC–PtII–Monophos Catalysts

“…Notably, 1,5‐enynes bearing an oxygenated function at the propargylic position have been widely used as suitable precursors for the bicyclic and polycyclic scaffolds of terpenoid derivatives. Relevant examples are the syntheses of sabinol,2 sabina ketone,3 cubebol,4 carenes,4b,5cedrene,6 and others,7 by gold‐ or platinum‐catalyzed rearrangements of enynes of this class. The highly desirable access to these and analogous bicyclic scaffolds in enantiomerically enriched form has been envisioned so far by either diastereoselective cyclizations or chirality transfer from enantiomerically enriched substrates 2,4.…”