Diastereoselective Addition of Prochiral Nucleophilic Alkenes to a-Chiral N-Sulfonyl Imines

The Lewis acid catalyzed addition of prochiral E and Z allyl nucleophiles to chiral -alkoxy N-tosyl imines is described. Alkene geometry is selectively transferred to the newly formed carbon-carbon bond, resulting in stereochemical control of C2, C3, and C4 of the resulting 2-alkoxy-3-N-tosyl-4-alkyl-5-hexenes. The C3 and C4 diastereoselectivity (dr) is influenced by the geometry of the alkene, size of N-sulfonyl substituent, and steric bulk of the substituted -alkoxy ether group. This work demonstrates that three of the four possible diastereomers can be synthesized in high diastereoselectivity and high yields using the current methods. A mechanistic computational analysis to elucidate the high selectivity is also presented.