Reaction of hydrazonoyl chlorides to trimethylsilyl homoallyl ethers

Title reaction gave mainly 4,5-dihydropyrazole derivatives due to nitrilimine cycloaddition onto the ethylenic bond. Cycloaddition regioselectivity was good despite the electronic demands of the substituents placed to the ethylenic dipolarophile are quite similar. Metalated transition states have been proposed in order to account the observed regioselectivity. Highly substituted cyclopropanes were also formed due to the electrophilic attack of a nitrilium-like carbocation to the ethylenic bond.