Dialkoxycarbenes in (4 + 1) Cycloadditions: Application to the Synthesis of Carotol.

Dialkoxycarbenes are more reactive than NHCs and participate in many reactions including a formal (4 + 1) cycloaddition with electron-deficient dienes. We have learned to control the relative stereochemistry of the newly created chiral carbons in this process and now report that, combined with a chiral auxiliary, it has been used successfully in a short and efficient synthesis of the sesquiterpene carotol.