N‐Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals and o‐Quinone Methides: Highly Enantioselective Synthesis of Benzo‐ε‐Lactones

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

“…Ye reported an enantioselective formal [3+4] annulation between enals and o -quinone methides in 2013. 153 While both aryl and aliphatic enals participate in the reaction, the scope was limited to dioxolane-fused o -quinone methides bearing an aryl substituent off the exo-olefin. This protocol addresses the potential [3+2] side reaction by taking advantage of the driving force of rearomatization from the [3+4] reaction.…”

Formal Asymmetric Catalytic Thiolation with a Bifunctional Catalyst at a Water–Oil Interface: Synthesis of Benzyl Thiols

“…[2] However,d espite their broad synthetic utility,o nly very few catalytic systems have been reported to date on the enantioselective addition to o-QMs (Scheme 1). [3] Chiral organocatalysts,i ncluding quaternary ammonium salts, [4] N-heterocyclic carbenes, [5] and chiral BINOL, [6] have been employed to activate various nucleophiles for the [4+ +2] cycloaddition, the [4+ +3] cycloaddition, and the conjugated addition to o-QMs,r espectively (Scheme 1). [3] Chiral organocatalysts,i ncluding quaternary ammonium salts, [4] N-heterocyclic carbenes, [5] and chiral BINOL, [6] have been employed to activate various nucleophiles for the [4+ +2] cycloaddition, the [4+ +3] cycloaddition, and the conjugated addition to o-QMs,r espectively (Scheme 1).…”

N‐Heterocyclic‐Carbene‐Catalyzed Synthesis of 2‐Aryl Indoles

“…Ultimately, the success of our approach would rely on concomitant generation of the Ao-QM and the NHC catalyst using a single Brønsted base species along with balancing the concentrations of each reactive intermediate during the course of the reaction (i.e., 1b and 1c ). [19] Additionally, it was undetermined if the Lewis basic NHC catalyst would directly trap a reactive electrophile 1c . Initial experiments with benzyl chloride 2 and benzaldehyde in the presence of precatalysts A or B with DBU yielded the desired ketone 3 in moderate to low yield (Table 1, entry 1-2).…”