Intramolecular [4 + 3] cycloadditions – Stereochemical issues in the cycloaddition reactions of cyclopentenyl cations – A synthesis of (+)-dactylol

Five cyclopentanones were prepared for the purpose of examining the effects of stereogenic centers on the course of the intramolecular [4 + 3] cycloaddition reactions of cyclopentenyl cations. One substrate reacted with very high levels of diastereoselectivity and was converted to (+)-dactylol. The cyclopentenone without stereogenic centers on the tether or the five-membered ring gave two cycloadducts, the endo isomer being only slightly favored over the exo. Other substrates reacted with generally good to poor stereoselectivity. An epimer of the substrate leading to (+)-dactylol afforded all possible isomers of the cycloadduct with relatively poor stereoselectivity.Key words: cycloaddition, total synthesis, dactylol.