Stereoselective synthesis of syn,syn-2-methyl-1,3-diols through one-pot aldol–reduction sequence

Chx2BCl-mediated syn-aldol reaction of the α-OTBS lactate-derived ketone 1 followed by in situ reduction of the resulting boron aldolate with LiBH4 lead to complete stereoselectivity for the boronates 2 in 80–95% yields. Then, a very mild oxidative work-up of 2 (H2O2/NaOAc in THF–H2O) allows isolation of syn,syn-2-methyl-1,3-diols 3 in yields up to 95% without migration of the TBS group.