Generality-Driven Catalyst Development: A Universal Catalyst for Enantioselective Nitroalkene Reduction.

Cracking the selectivity-generality paradox is among the most pressing challenges in asymmetric catalysis. This obstacle prevents the immediate and successful translation of new methods to diverse small molecules. This is particularly rate-limiting for therapeutic development, where availability and structural diversity are often critical components of successful campaigns. Here we describe the union of generality-driven enantioselective catalysis and the preparation of diverse peptidomimetics. A single new organocatalyst provides high selectivity and substrate generality that is matched only by a combination of metal and organocatalysts. Within organocatalysis, this discovery breaks a 16-year monolithic paradigm, uncovering a powerful new scaffold for enantioselective reduction with behavior that suggests the recognition of a nitroethylene minimal catalaphile.

Preparation of N-Aryl Amides by Epimerization-Free Umpolung Amide Synthesis.

Amide synthesis is one of the most widely practiced chemical reactions, owing to its use in drug development and peptide synthesis. Despite the importance of these applications, the attendant effort to eliminate waste associated with these protocols has met with limited success, and pernicious α-epimerization is most often minimized but not eliminated when targeting challenging amides (e.g., N-aryl amides). This effort has focused on what is essentially a single paradigm in amide formation wherein an electrophilic acyl donor reacts with a nucleophilic amine. Umpolung amide synthesis (UmAS) emerged from α-halo nitroalkane reactions with amines and has since been developed into a method for the synthesis of enantiopure amides using entirely catalytic, enantioselective synthesis. However, its inability to forge N-aryl amides has been a longstanding problem, one limiting its application more broadly in drug development where α-chiral N-aryl amides are increasingly common. We report here the reaction of α-fluoronitroalkanes and N-aryl hydroxyl amines for the direct synthesis of N-aryl amides using a simple Brønsted base as the promoter. No other activating agents are required, and experiments guided by mechanistic hypotheses outline a mechanism based on the UmAS paradigm and confirm that the N-aryl amide, not the N-aryl hydroxamic acid, is the direct product. Ultimately, select chiral α-amino-N-aryl amides were prepared with complete conservation of enantioenrichment, in contrast to a parallel demonstration of their ability to epimerize using the conventional amide synthesis alternative.

Enantioselective iodolactonization to prepare ε-lactone rings using hypervalent iodine.

Despite the rapid growth of enantioselective halolactonization reactions in recent years, most are effective only when forming smaller (6,5,4-membered) rings. Seven-membered ε-lactones, are rarely formed with high selectivity, and never without conformational bias. We describe the first highly enantioselective 7-exo-trig iodolactonizations of conformationally unbiased ε-unsaturated carboxylic acids, effected by an unusual combination of a bifunctional BAM catalyst, I2, and I(iii) reagent (PhI(OAc)2:PIDA).