Effective 1,4-asymmetric C-C/C-O stereoinduction in indium-promoted coupling reactions of aldehydes to protected and unprotected [1-(bromomethyl)vinyl] alkanols. The status of intramolecular chelation within functionalized allylindium reagents

The stereochemistry of the coupling reactions of oxygen-substituted bromides 8-10 with isobutyraldehyde, benzaldehyde, and cyclohexanecarboxaldehyde in water is described. The examples involving the O-silylated derivatives 8 exhibit moderate anti stereoselectivity. In contrast, rather high (most often in excess of 80:20) syn diastereofacial bias is observed when hydroxy bromides 10 are involved. Consequently, stereocontrolled 1,4-asymmetric induction under aqueous conditions can be realized in either direction on demand. These results are considered to reflect the fact that the siloxy systems enter into C-C bond formation via conventional Felkin-Anh transition state arrangements. The crossover observed for the unprotected analogues is believed to be a consequence of the preferred adoption of chelated transition states, these interactions likely being fundamental to aqueous organometallic chemistry.