Stereoselective Hydride Reduction of Tetronic Acid Derivatives. Synthesis of Branched-Chain TetrofuranosesSummary The 3-methoxymethyl derivatives of 2-methyl-~, L-threofuranose (10a) and 2-deoxy-2-methyl-~, L-erythrofuranose (1 1 a) are prepared starting from 2-methyltetronic acid (1). The key step is the stereoselective reduction of the 3-0x0-function of 2-chloro-2-methyl-3-oxo-y-butyrolacton (2) by sodiumborohydride, which proceeds predominantly anti with respect to the C, C1-bond. The configuration of the reduction products has been established by 'H-and '3C-NMR.-spectroscopy.