Stereoselective Aldol Addition to Rhenium(I) Complexes and Reversible Dimerization with Epimerization of the Metal Center

Herein, we report several examples of stereoselective aldol additions of aldehydes or ketones to ReI tricarbonyl complexes to form monomeric derivatives in good yields. The metal‐centered chirality defines the final stereochemistry of the carbon atom of the monomeric ReI complex after the addition. However, it cannot control the resulting stereochemistry of the enolate part, and thus, if the α‐carbon atom of the reagent is prochiral, a mixture of diastereoisomers is obtained. On the other hand, all of the monomeric complexes can be reversibly dimerized in basic media to form cis dimers, for which an epimerization of the metal‐centered chirality is required in order to avoid steric congestion. All of these results are supported by exhaustive crystallographic analysis.This research was supported by the Spanish Ministerio de Ciencia e Innovación (CTQ2009‐12111) and Junta de Castilla y León (VA070 A08 and GR Excelencia 125). R.G.‐R. and C.M.A. wish to acknowledge an MEC‐FPU grant and a Ramón y Cajal contract.Peer Reviewe