Hydrogen-bond (HB)-donor catalysts that bear a 2-aminoquinazolin-4-(1H)-one or a 3-aminobenzothiadiazine-1,1-dioxide skeleton have been developed, and it has been shown that these catalyst motifs act similarly to other HB-donor catalysts such as thioureas. The highly enantioselective hydrazination of 1,3-dicarbonyl compounds was realized even at room temperature with up to 96% ee for 2-aminoquinazolin-4-(1H)-one-type catalysts, which were more effective than the corresponding urea and thiourea catalysts. In addition, benzothiadiazine-1,1-dioxide-type catalysts were shown to promote the isomerization of alkynoates to allenoates with high enantioselectivity. To overcome the problem that the products were obtained as mixtures with the starting alkynoates, we developed the tandem isomerization and cycloaddition of alkynoates for the synthesis of advanced chiral compounds such as bicyclo[2.2.1]heptenes and 3-alkylidene pyrrolidine without a significant loss of enantioselectivity.

The NHC-catalyzed thioesterification of aromatic or aliphatic aldehydes with a range of thiols was developed in the presence of a stoichiometric amount of an organic oxidant. Among the oxidants examined, phenazine was shown to give the best results in terms of chemical yield and compatibility with thiols.

SummaryAn efficient catalytic synthesis of α-amino-β-keto esters has been newly developed. Cross-coupling of various aldehydes with α-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to α-amino-β-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the α-amino-β-keto esters are formed under thermodynamic control.

A chiral bifunctional thiourea-catalyzed Mannich reaction of diethyl 2-isocyanatomalonate with N-sulfonylimines was described. The tandem cyclization proceeded smoothly after Mannch reaction, directly furnishing chiral 2-imidazolidinones in 72-99% yields with 83-98% ees. Sterically demanding sulfonyl group was crucial for aliphatic imines to afford the corresponding product in high enantioselectivity.