5-En-1-yn-3-ol substrates bearing a free hydroxyl group or an acyl group are highly versatile partners for PtCl2-catalyzed cycloisomerizations. Electrophilic activation of the alkyne moiety triggers at wish a hydride or an O-acyl migration yielding at the end to regioisomeric keto derivatives. The efficient preparation of Sabina ketone, an important monoterpene precursor, has been worked out.
A Gold-Catalyzed Entry into the Sesquisabinene and Sesquithujene Families of Terpenoids and Formal Total Syntheses of Cedrene and Cedrol
作者:Alois Fürstner、Andreas Schlecker
DOI:10.1002/chem.200801382
日期:2008.10.20
into the bicyclic cyclopropyl ketone derivatives 5 and 6 by way of a gold-catalyzed Ohloff-Rautenstrauch-type enynecycloisomerization is described. The required substrates were prepared by an asymmetric addition of the branched allylzinc reagent 21 to the alkynyl aldehyde 17 mediated by the deprotonated bisoxazoline (BOX) ligand 22. Compounds 5 and 6 were then converted into a host of different members
1,5-Enynes are highly reactive under PtCl2 catalysis and give a range of [3.1.0] bicyclic skeletons. The scope and limitations of this process are presented. Regioisomeric keto derivatives are obtained depending upon the nature of the oxygenated substituent at the propargylic position of the starting substrate.