TiCl4-Mediated Reduction of 1,3-Diketones with BH3−Pyridine Complex: A Highly Diastereoselective Method for the Synthesis of syn-1,3-Diols

(formula presented) 1,3-Diketones can be reduced in high yields and with excellent diastereoselectivity to the corresponding syn-1,3-diols by carrying out the reaction with BH3-pyridine complex in CH2Cl2 at -78°C in the presence of an equivalent of TiCl4 and 0.1 equiv of pyridine. This protocol shows a general character: excellent results are obtained when the groups bound to the carbonylic functions are linear or branched carbon chains and aromatic or benzylic frameworks as well.