1‑Hydroxybenzotriazole-Assisted, N‑Heterocyclic Carbene Catalyzed β‑Functionalization of Saturated Carboxylic Esters: Access to Spirooxindole Lactones

A 1-hydroxybenzotriazole-assisted, N-heterocyclic carbene catalyzed direct β-functionalization of saturated carboxylic esters is disclosed. This formal [3 + 2] annulation reaction of carboxylic esters with isatins affords optically pure spirooxindole lactones (on gram scale) bearing two vicinal stereogenic centers. A dual role of HOBt is proposed based on controlled experiments to rationalize the enhancement of diastereoselectivity and enantioselectivity

Oxidative Asymmetric [2 + 3] Annulation of Aldehydes with Azomethine Imines Enabled by <i>N</i>‑Heterocyclic Carbene Catalysis

An efficient asymmetric [2 + 3] annulation of simple aldehydes with <i>N</i>,<i>N</i>′-cyclic azomethine imines via oxidative <i>N</i>-heterocyclic carbene (NHC) catalysis is disclosed, affording bicyclic pyrazolidinones bearing two vicinal tertiary stereogenic centers with moderate to good yields (56–84% for 19 examples), good to excellent diastereoselectivities (>20:1 for 17 examples), and good to excellent enantioselectivities (66–98% for 19 examples). This direct α-carbon functionalization reaction of aldehyde can be readily performed on gram scale under mild conditions, and a five-membered transition state is proposed to rationalize the stereochemical outcome

Oxidative Asymmetric [2 + 3] Annulation of Aldehydes with Azomethine Imines Enabled by <i>N</i>‑Heterocyclic Carbene Catalysis

An efficient asymmetric [2 + 3] annulation of simple aldehydes with <i>N</i>,<i>N</i>′-cyclic azomethine imines via oxidative <i>N</i>-heterocyclic carbene (NHC) catalysis is disclosed, affording bicyclic pyrazolidinones bearing two vicinal tertiary stereogenic centers with moderate to good yields (56–84% for 19 examples), good to excellent diastereoselectivities (>20:1 for 17 examples), and good to excellent enantioselectivities (66–98% for 19 examples). This direct α-carbon functionalization reaction of aldehyde can be readily performed on gram scale under mild conditions, and a five-membered transition state is proposed to rationalize the stereochemical outcome