Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Chloro(cyclopentadienyl)bis(1,2:5,6‐di‐<jats:italic>O</jats:italic>‐isopropylidene‐α‐<jats:sc>D</jats:sc>‐glucofuranos‐3‐<jats:italic>O</jats:italic>‐yl)titanium (<jats:bold>1</jats:bold>) 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 (<jats:italic>E</jats:italic>)enolate<jats:bold>13</jats:bold>of 2,6‐dimethylphenyl propionate (<jats:bold>11</jats:bold>) adds to the<jats:italic>re</jats:italic>‐side of aldehydes, affording various<jats:italic>syn</jats:italic>‐aldols<jats:bold>14</jats:bold>with high dia‐ and enantioselectivity (92–97% ds, 91–97% ee,<jats:italic>cf</jats:italic>.<jats:italic>Scheme 2</jats:italic>and<jats:italic>Table 1</jats:italic>). Racemic<jats:italic>syn</jats:italic>‐aldols (±)‐<jats:bold>14</jats:bold>are obtained analogously from the achiral bis(2‐propyloxy)‐Ti‐enolate<jats:bold>15</jats:bold>(<jats:italic>Scheme 2</jats:italic>and<jats:italic>Table 2</jats:italic>). In contrast to the unstable Li‐enolate<jats:bold>10</jats:bold>, the Ti‐enolates<jats:bold>13</jats:bold>and<jats:bold>15</jats:bold>isomerize at −30°, presumably to the thermodynamically more stable (<jats:italic>Z</jats:italic>)‐enolates (<jats:italic>Scheme 4</jats:italic>), While the diastereoselectivity of the achiral enolate<jats:bold>15</jats:bold>is lost upon this equilibration, the chiral (<jats:italic>Z</jats:italic>)‐enolate<jats:bold>27</jats:bold>quite unexpectedly affords<jats:italic>anti</jats:italic>‐aldols<jats:bold>12</jats:bold>of high optical purity (94–98% ec) 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 synepimers of moderate optical purity (<jats:italic>Scheme 5 and Table 3).</jats:italic>Consistent with these findings, re‐facial‐and ami ‐selective aldol‐addition is also exhibited by the (<jats:italic>Z</jats:italic>)‐configurated Ti‐enolate<jats:bold>22</jats:bold>of<jats:italic>N</jats:italic>‐propionyl‐oxazolidi‐none<jats:bold>19</jats:bold>(<jats:italic>Scheme 3</jats:italic>).</jats:p>