Total synthesis of dimethyl gloiosiphone A via alpha-carbonyl radical spiro-cyclization

A general approach toward spiro[4.4]nonane structure based on the cr-carbon yl radical cyclization has been developed. Efficient total synthesis of dim ethyl gloiosiphone A (2) was achieved. Thus, alkylation of the anion of dim ethylhydrazone of cyclopentanone with 5-iodopent-1-yne followed by hydrolys is gave ketone 4. Iodination of 4 via its TMS-enol ether yielded iodo keton e 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 2 4. Methylation of 24 furnished methoxy iodo enone 25. Substitution of iodid e in 25 with methoxide produced dimethoxy enone 26. Allylic oxidation of 26 gave diketone 27. Treatment of 27 with OsO4, and N-methylmorpholine N-oxid e gave dihydroxy ketone 28. Methylation of the primary alcohol group in 28 afforded dimethyl gloiosiphone A (2).