The reduction of 6-hydroxy-/l-ketoesters 1 was investigated with three different reducing agents. In several instances, high selectivity in favor of syn-1.3-diols was observed.Stereoselective preparation of the 1,3-diol function has great utility in synthetic organic chemistry due to the occurrence of these fragments in several natural products. In connection with our work on compactin analogues [l], we needed an efficient and general method for preparing syn-l,3-diols.Towards this objective, we have prepared [2] a series of 6-hydroxy-P-ketoesters 1 (Scheme I ) by the addition of acetoacetate dianion to the respective aldehydes and investigated their reductions with different agents.Stereoselective reductions of 8-hydroxy-ketones utilizing metal-chelation control have recently been reported in the literature. The boron-chelate method [3], which gives excellent selectivity in favor of the syn -dials, invokes cyclic complexes 3 for explaining the stereochemical outcome of the reduction. In the alternative Zn(BH,), method [4], the setup for the reduction is presumed to be 4. At the outset of our investigations with 6-hydroxy-P-ketoesters, we were intrigued by the possibility that a simple H-bond as shown in 5 may provide a sufficiently strong bridge for achieving the desired syn-selectivity . Accordingly, we examined the hydrogenation of la2) using 5 % Pt/C (room temperature, 50 psi) in MeOH. Under these condi-') ') Present address: Ciba-Geigy AG, CH-4002 Basel. All the hydroxy-ketoesters la-k described are derived from the addition of acetoacetate dianion to the corresponding aldehydes, following [2].

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