Synlett 2012(7): 990-1006  
DOI: 10.1055/s-0031-1290657
ACCOUNT
© Georg Thieme Verlag Stuttgart ˙ New York

Copper-Catalyzed Cycloisomerizations of Enynols and Their Esters

Charles Fehr*
Firmenich SA, Corporate R&D Division, P. O. Box 239, 1211 Geneva 8, Switzerland
Fax: +41(22)7803334; e-Mail: charles.fehr@firmenich.com; e-Mail: cgfehr@bluewin.ch;
Further Information

Publication History

Received 11 September 2011
Publication Date:
05 April 2012 (online)

Abstract

We have discovered that several platinum- or gold-catalyzed cycloisomerization reactions can also be catalyzed by copper. This Account discusses our new findings, the complementarity of copper-catalysis, and its application to the synthesis of (-)-cubebol, (-)-β-santalol, and other fragrance compounds.

1 Introduction

2 Cycloisomerization of 5-en-1-yn-3-ols: The Cyclopropanation Pathway

3 Cycloisomerization of 5-En-1-yn-3-ol-Derived Esters and Synthesis of (-)-Cubebol

4 Cycloisomerization of a 6-En-1-yn-3-ol and Its Corresponding Acetate towards the Synthesis of Thujopsanone-Like Compounds

5 Cyclization-Fragmentations of 5-En-1-yn-3-ols

6 Synthesis of (-)-β-Santalol by Cyclization-Fragmentation of a 5-En-1-yn-3-ol

7 Reactivity of 6-En-1-yn-4-ols: Cyclization-Fragmentation vs. Metathesis Reaction

8 Conclusions and Outlook

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Surprisingly, 90 and to a larger extent 91 showed a diminished ee as compared to 88 and 89, although the dr remained the same. Possibly, 90 and 91 undergo a thermal 1,2-H shift.

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Migration of the cyclopropane C-C bond opposite to the C-C=M bond in 99b (Scheme  [²7] ) and 105b (Scheme  [²8] ) leads to the same metathesis product. These reactions proceed via nonclassical cations, but for clarity we prefer not to draw partial bonds.

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Kindly performed by Professor M. Santelli (University of Aix-Marseille, France).