ChemInform Abstract: Regiocontrol of Radical Cyclization by Lewis Acids. Efficient Synthesis of Optically Active Functionalized Cyclopentanes and Cyclohexanes.
Abstract
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ChemInform Abstract
Optically active α-alkylidenelactones (I) undergo a regioselective 5-exo radical cyclization by treatment with Bu3SnH and a catalytic amount of Et3B to give cyclopentane products (II) predominantly or exclusively. If the reaction is performed in the presence of Et2AlCl, only the alkyl-substituted lactones undergo a regioselective 6-endo cyclization to give cyclohexane derivatives (III) predominantly, whereas the reaction of lactones (Ic) and (Id) results in reduction of the olefin and iodo moieties and no cyclohexane derivatives are isolated. In addition, the use of product (IIIa) as starting compound for some carbocycles is demonstrated.
