Organocatalytic Asymmetric [4 + 2] Cyclization of Azadienes with Azlactones: Access to Chiral 3-Amino-δ-Lactams Derivatives

Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions

“…[16b] In the desired transformation, product 10 a is obtained by first cyclizing 8 a to the azaortho-quinone methides intermediate under the Ph 3 PAuBF 4 catalyst, followed by the Lewis base-catalyzed (4 + 2) cycloaddition with esters 9 a. [17] However, the presence of cationic gold catalyst largely prohibits the activity of Lewis base Table 1: Substrate Scope with Respect to the Imine. [a] [a] Reaction conditions: 1 a (0.15 mmol), NEt 3 (0.20 mmol), TsCl (0.18 mmol), THF (1 mL) 0 °C; then 2 (0.10 mmol), (Ra,S,S)-AxBTM-6 (2.5 mol %), NEt 3 (0.20 mmol).…”

Stereoselective skeletal modification of tryptanthrins to install chiral piperidine-2-ones enabled by Brønsted acid catalysis

“…In particular, azlactones could readily participate in various asymmetric [ n + 2] annulations under CPA catalysis. 14 Based on these considerations, we herein describe an asymmetric formal [4 + 2] cyclisation between aza-dienes derived from simple tryptanthrins and azlactones, enabled by the catalysis of a chiral BINOL-derived phosphoric acid. This catalytic protocol shows excellent reactivity toward the tryptanthrin-derived substrates, and various novel piperidine-2-one-fused tryptanthrins can be rapidly accessed under mild reaction conditions (Scheme 1c).…”