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Highly enantioselective intermolecular hydroamination of allylic amines with chiral aldehydes as tethering catalysts.

Asymmetric catalysis is of enormous academic and industrial importance as a highly efficient approach to enantioenriched organic molecules. Enzymes and bifunctional catalysts are among the most efficient systems available to perform difficult intermolecular reactions with nearly perfect stereocontrol. This efficiency stems from their ability to perform substrate activation while favoring substrate preassociation and preorganization. However, highly efficient asymmetric catalysis does not require both activation methods. Many asymmetric catalysts achieve high enantioselectivities by performing substrate activation in a chiral environment alone. In contrast, and despite the possibility of accelerating intermolecular reactions by a factor of 10 to 10 through substrate preassociation, catalytic reactions relying exclusively on temporary intramolecularity are rare, and highly efficient examples of such asymmetric catalysis have not been reported. Herein, we show that chiral aldehydes are capable tethering asymmetric catalysts, leading to highly enantioenriched vicinal diamine motifs through temporary intramolecularity alone. Recently, we reported that aldehydes catalyze intermolecular Cope-type hydroaminations of allylic amines via the formation of a temporary tether [(Eq. (1)]. In contrast to common tethering strategies, which rely on the stepwise assembly and cleavage of a tether, this approach uses aldehydes as catalysts to access a transient mixed aminal in situ and thus allow a facile “intramolecular” hydroamination. Although encouraging enantioselectivities suggested that transfer of stereochemical information from chiral aldehydes was possible (4 examples, 47–87 % ee), initial efforts were thwarted by catalyst epimerization and reproducibility issues. Seeking to develop an enantioselective hydroamination approach to synthetically useful vicinal diamines and to establish that highly efficient stereoinduction is possible by means of tethering catalysis, we embarked on a systematic survey of chiral aldehyde catalysts and reaction conditions (selected data shown in Table 1). In a previous communication, we had shown that commercially available (R)-glyceraldehyde acetonide (1 a) led to