Synthesis of the C-13 Side Chain Precursors of the 9-Dihydrotaxane Analogue ABT-271

N-Boc-l-Leucinol was converted to two C-13 side chain precursors of the 9-dihydrotaxane analogue ABT-271. The trans-oxazolidine acid 4 and the cis-Boc-lactam 2b were prepared in 44% and 40% overall yield, respectively, and with excellent (>98%) stereochemical purity.