Stereoselective nitrile oxide cycloadditions to chiral allyl ethers and alcohols. The inside alkoxy effect

We have studied the stereoselectivities of nitrile oxide cycloadditions to a variety of alkenes substituted by chiral allylic ether and alcohol units.²⁻⁸ The experimental results, combined with theoretical studies, lead us to propose that allylic ethers adopt the inside position and alkyl substituents prefer the sterically less crowded anti conformation in transition states for these electrophilic cycloadditions. This “inside alkoxy” effect is useful for predicting stereoselectivities of a host of electrophilic reactions with chiral allylic ethers.