Rearrangement Approaches to Cyclic Skeletons. IX. Stereoselective Total Synthesis of (±)-Camphorenone Based on a Ring-Contraction of Bicyclo[3.2.1]oct-6-en-2-one. Reliable One-Step Diazo Transfer Followed by a Wolff Rearrangement

A direct diazo transfer reaction to bicyclo[3.2.1]oct-6-en-2-ones and related compounds was accomplished by treatments with 2,4,6-triisopropylbenzenesulfonyl azide and potassium t-butoxide at −78 °C in THF. A Wolff rearrangement of the resulting α-diazoketones in the presence of water gave ring-contraction products, bicyclo[2.2.1]heptenecarboxylic acids. Using these two transformations the total synthesis of (±)-camphorenone was achieved stereoselectively, starting from 1-methoxybicyclo[2.2.2]oct-5-en-2-one.