Concise Synthesis of Xyloketal C Analogues

The synthesis of xyloketal C analogues 12-methylxyloketal C(8) and 12-dehydroxylxyloketal C(11) have been accomplished in three steps, which featured the radical cyclisation as the key step. This is the shortest approach to construct the B C ring systems of the type of ketal skeleton reported to date. The structures of title compounds were elucidated by spectroscopic data and X-ray structure analysis. The final radical cyclisations give mainly the cis-fused anti-substituted stereoisomers.