Chloro(cyclopentadienyl)bis( 1,2 : 5.6-di-0 -isopropylidene-cc -~-glucofuranos-3-0 -yl)titanium (1) is used for the transmetallation of Li-enolates obtained from propionyl derivatives. While such Ti-enolates of ketones and hydrazones appear to be unreactive, the (E)-enolate 13 of 2.6-dimethylphenyl propionate (1 1) adds to the re-side of aldehydes, affording various s-vn-aldols 14 with high dia-and enantioselectivity (92-97% ds, 91-97% ee, cJ Scheme 2 and Table 1). Racemic syn-aldols (f)-14 are obtained analogously from the achiral bis(2-propyloxy)-Tienolate 15 (Scheme 2 and Table 2). In contrast to the unstable Li-enolatc 10, the Ti-enolates 13 and 15 isomerize at -30", presumably to the thermodynamically more stable (L)-enolates (Scheme 4 ) . While the diastereoselectivity of the achirdl enolate 15 is lost upon this equilibration, the chiral (Z)-enolate 27 quite unexpectedly affords unti-aldols 12 of high optical purity (94~-98 % ee) and, in most cases, with acceptable-to-good diastereoselectivity (82-90% ds). Notable exceptions are branched unsaturated and aromatic aldehydes which form a greater proportion of sy-epimers of moderate optical purity (Scheme 5 and Table 3). Consistent with these findings, re-facialand anti-selective aldol-addition is also exhibited by the (Z)-configurated Ti-enolate 22 of N-propionyl-oxazolidinone 19 (Scheme 3). 1.Introduction. -In previous communications [l], we have described the synthesis of chloro(cyclopentadienyl)bis( 1,2 : 5,6-di-0 -isopropylidene-a -~-glucofuranos-3-0 -yl)-titanate (1) from [TiCpCl,] (2) and diacetoneglucose (DAGOH) 3. The novel complex 1, whose structure was studied by X-ray diffraction analysis, 'H-, and "C-NMR [ld], proved to be a potent chiral template for enantioselective reactions. Exchange of the C1-atom in 1 for ally1 (+ 4) or ester-enolates (+ 5 or 6) and reaction with aldehydes gives homoallyl alcohols 7 [la], /I-hydroxy-esters 8 [ 1 b], and threo-& hydroxy-a -amino acids 9 [lc], respectively, with high enantio-and diastereoselectivity (Scheme I ) . This accomplishment led to the experiments with propionyl-enolates described below.The stereocontrolled aldol addition of propionyl-enolates is one of the most important reactions for the construction of complex acyclic or macrocyclic natural products of propionate/acetate biogenesis 121. While excellent methods are known for the enantioselective synthesis of syn -aldols (cf.

The syn products, e.g. (III), of the title reaction are most likely formed via the E Ti‐enolate of the starting compound (I).