Samarium Diiodide-Promoted Intramolecular Radical Cyclization of (η⁴-Diene)Fe(CO)₃ Complexes Bearing Keto Side Chains

Abstract

Reaction of samarium diiodide with (η 4 -cyclohexadiene)Fe(CO) 3 complexes bearing keto side chains in THF/HMPA/ t -BuOH gives fused bicyclo[4.3.0]nonenol derivatives, whereas (η 4 -cycloheptadiene)Fe(CO) 3 analogues produce a bicyclo[5.3.0]decenol ring skeleton. The iron-mediated intramolecular radical addition allows for the direct stereocontrol of three contiguous stereogenic centers of these fused bicyclic skeletons. Under the same reaction conditions, intramolecular ketyl radical cyclization of acyclic (η 4 -1,3-butadiene)Fe(CO) 3 complexes with keto side chains at the terminal position of the diene ligands furnishes disubstituted cyclopentanol and cyclohexanol derivatives with excellent diastereoselectivity.