Chemo- and regioselective hydroboration of Δ14,15 in certain cephalostatin analogue

The symmetrical diketone II, which can be synthesized in gram scale using a well established method, was used as a starting material to prepare the 11α-methoxy ketomethylene VI. This is in continuation of our study aiming at the synthesis of multi-hydroxylated cephalostatin analogues, as for example cephalostatin 1 I, a potent anti-tumor natural product. Compound VI underwent chemo- and regioselective hydroboration reaction at only one of Δ14,15 double bonds furnishing compound IX as a major product in a fair yield.