Catalytic enantioselective synthesis of α-aryl α-hydrazino esters and amides

Asymmetric 1,2-addition of aryl boronic acids to N-carbamoyl (Cbz and Fmoc) protected glyoxylate-derived hydrazones affords α-aryl α-hydrazino esters/amides, key building blocks en route to artificial peptides.

Catalytic enantioselective ene-type reactions of vinylogous hydrazone: construction of α-methylene-γ-butyrolactone derivatives

Catalytic asymmetric ene-type reactions of vinylogous hydrazone with isatins, α-ketoester, imines and aldehydes were accomplished which gave an environmentally friendly, straightforward approach to afford bioactive chiral α-methylene-γ-butyrolactone derivatives.

Highly stereoselective [4+2] and [3+2] spiroannulations of 2-(2-oxoindolin-3-ylidene)acetic esters catalyzed by bifunctional thioureas

A new Michael-Michael cascade reaction between 2-(2-oxoindolin-3-ylidene)acetic esters 1 and nitroenoates 2, catalyzed by bifunctional thioureas, is investigated. The combination of the two Michael reactions results in a novel and facile [4+2] or [3+2] spiroannulation process, which is characterized by the following features: 1) two carbon-carbon bonds and four stereocenters, including a quaternary spiro carbon, are formed under mild conditions; 2) an unprecedented and stereochemically defined substitution pattern on the spirocarbocyclic unit is obtained; 3) the double-bond configuration of the donor-acceptor nitroenoate 2 determines the absolute configuration of the spiro center, whereas the remaining stereocenters are formed under control of the catalyst. The effect on the final stereochemical outcome of structural variations of each starting material, catalyst, and experimental conditions is analyzed in detail. In particular, the use of specifically designed chiral nitroenoates enables diverse polyfunctional spirocyclohexane derivatives containing six consecutive stereogenic centers to be constructed. To our knowledge, this is the first asymmetric organocatalytic strategy enabling both five- and six-membered β-nitro spirocarbocyclic oxindoles.

N,N'-Bis[3,5-bis(trifluoromethyl)phenyl]thiourea: a privileged motif for catalyst development

Over the last decade, the use of (thio)urea derivatives as organocatalysts in organic chemistry has increased rapidly. One of the key features is their ability to activate substrates and subsequently stabilize partially developing negative charges (e.g., oxyanions) in the transition states employing explicit double hydrogen bonding. Among (thio)urea-based catalysts, N,N'-bis[3,5-bis(trifluoromethyl)phenyl]thiourea developed by Schreiner's group (abbreviated here as Schreiner's thiourea) has played a very important role in the development of H-bond organocatalysts. Nowadays it is used extensively in promoting organic transformations, and the 3,5-bis(trifluoromethyl)phenyl motif thereof is used ubiquitously in H-bond catalysts. This review summarizes the key developments of Schreiner's thiourea-mediated reactions with the aim to further expand the applications of (thio)urea-based catalysts.