Novel formation of a bridged bicyclic furan by rearrangement of a tetrahydroxydecalinone

In the course of a synthetic approach to the arisugacins, we prepared the tetrahydroxydecalinone 8a (which exists as the hydroxytetrahydrofuran 8b) by a straightforward route from hydroxy-β-ionone. On treatment with mesyl chloride and base, the desired mesylate 9 was not formed but rather 8ab underwent a novel rearrangement to produce the bridged bicyclic furan 10 in excellent yield. A reasonable mechanism for the rearrangement is presented involving a retro-aldol reaction, a base-catalyzed β-elimination, and final furan formation from a β-hydroxymethyl enone.