Total Synthesis of Dimethyl Glolosiphone A via α‐Carbonyl Radical Spiro‐Cyclization

A general approach toward spiro[4.4]nonane structure based on the α‐carbonyl radical cyclization has been developed. Efficient total synthesis of dimethyl gloiosiphone A ( 2 ) was achieved. Thus, alkylation of the anion of dimethylhydrazone of cyclopentanone with 5‐iodopent‐1‐yne followed by hydrolysis gave ketone 4 . Iodination of 4 via its TMS‐enol ether yielded iodo ketone 7 . Radical spiro‐cyclization of 7 gave spiro ketone 10 . Iodination of 10 afford iodo spiro ketone 23 . Oxidation and iodination of 23 gave compound 24 . Methylation of 24 furnished methoxy iodo enone 25 . Substitution of iodide in 25 with methoxide produced dimethoxy enone 26 . Allylic oxidation of 26 gave diketone 27 . Treatment of 27 with OsO 4 and N ‐methylmorpholine N ‐oxide gave dihydroxy ketone 28 . Methylation of the primary alcohol group in 28 afforded dimethyl gloiosiphone A ( 2 ).