1,3-Asymmetric Induction in Diastereoselective Allylations of Chiral N-Tosyl Imines

Abstract

Lewis acid mediated allylations of β-alkoxy N-tosyl imines using allyltrimethylsilane lead to 3-alkoxy homoallylic N-tosyl amines with anti-selectivity. Two methods of Cu­(OTf)2-mediated allylations are reported herein, demonstrating that diastereoselectivity can be achieved through 1,3 acyclic stereocontrol of β-chiral aldimines. Observed selectivity trends and computational evidence suggest selectivity arises through the formation of a six-membered ring chelate. The product ratios of these allylations are dependent on conformational preferences of the chelate and steric effects in the transition-state structures.

Diastereoselective Substitution Reactions of Acyclic β-Alkoxy Acetals via Electrostatically Stabilized Oxocarbenium Ion Intermediates

“…Substitution reactions of acetals bearing β-alkoxy groups proceeded with high diastereoselectivities (diasteromeric ratio (dr) of >90:10) in many cases (eq ). The products would be the same as those expected from chelation-controlled additions to β-alkoxy, α-substituted aldehydes, − but such intermediates cannot be invoked in the case of acetal substitution reactions. The alkoxy groups appear to stabilize the oxocarbenium ion intermediates by electrostatic interactions to form four-membered-ring structures resembling 2.…”

“…The alkoxy groups appear to stabilize the oxocarbenium ion intermediates by electrostatic interactions to form four-membered-ring structures resembling 2. This participation defines the conformation of the intermediate and thus establishes which face of the oxocarbenium ion is attacked. − …”