Oxidative radical cyclization of (ω-iodoalkyl)indoles and pyrroles. Synthesis of (-)-monomorine and three diastereomers

Article abstract of DOI:10.1021/jo00088a029

Addition of excess hydrogen peroxide (10 equiv) to a sonicated solution of FeSO₄:7H₂O (1 equiv) in DMSO containing the N-(ω-iodoalkyl)indoles 4, 5, 11, and 13 effected oxidative radical cyclization to 6, 7, 14, and 15, respectively. The (ω-iodoalkyl)pyrroles 21, 22, 27, 38, and 49 underwent analogous cyclization reactions to 23, 24, 28, 39, and 50, respectively. The regiochemistry of these radical cyclization reactions was correctly predicted by FMO calculations in all cases but one. For compound 38, FMO calculations indicated that radical attack should take place at both C-3 and C-5. Only the product of cyclization at C-5, i.e., 39, was observed. The enantiomerically pure bicyclic ketone 42, prepared by the above technique from the iodide 53, was converted into 55 which, on catalytic reduction (H₂/Rh-Al₂O₃), gave a mixture of (-)-monomorine (40) and three of its diastereomers 56-58.