Sequential Diels-Alder reaction/rearrangement sequence: synthesis of functionalized bicyclo[2.2.1]heptane derivatives and revision of their relative configuration.

Abstract

A sequential Diels-Alder reaction/rearrangement sequence was developed for the synthesis of diverse functionalized bicyclo[2.2.1]heptanes as novel floral and woody odorants. The outcome of the rearrangement depended on the substitution pattern of the dienes. 2D NMR analysis has established the correct relative configuration of the bicyclo[2.2.1]heptanone, which was originally misassigned. Furthermore, when the initiating DA reaction was catalyzed by a chiral Lewis acid, the bicyclo[2.2.1]heptane derivatives including (+)-herbanone can be obtained in an enantiomeric ratio (er) up to 96.5:3.5.