Efficient Access to Chiral Trisubstituted Aziridines via Catalytic Enantioselective Aza‐Darzens Reactions

Herein, we report a Zn‐ProPhenol catalyzed aza‐Darzens reaction using chlorinated aromatic ketones as nucleophilic partners for the efficient and enantioselective construction of complex trisubstituted aziridines. The α‐chloro‐β‐aminoketone intermediates featuring a chlorinated tetrasubstituted stereocenter can be isolated in high yields and selectivities for further derivatization. Alternatively, they can be directly transformed to the corresponding aziridines in a one‐pot fashion. Of note, the reaction can be run on gram‐scale with low catalyst loading without impacting its efficiency. Moreover, this methodology was extended to α‐bromoketones which are scarcely used in enantioselective catalysis because of their sensitivity and lack of accessibility.     

Catalytic Enantioselective Aza‐Piancatelli Rearrangement

An efficient organocatalytic enantioselective aza‐Piancatelli rearrangement is disclosed. The powerful process provides rapid access to valuable chiral 4‐amino‐2‐cyclopentenone building blocks from readily available 2‐furfurylcarbinols with excellent chemo‐, enantio‐, and diastereoselectivities under mild reaction conditions.     

Phosphite‐Catalyzed C−H Allylation of Azaarenes via an Enantioselective [2,3]‐Aza‐Wittig Rearrangement

A phosphite‐mediated [2,3]‐aza‐Wittig rearrangement has been developed for the regio‐ and enantioselective allylic alkylation of six‐membered heteroaromatic compounds (azaarenes). The nucleophilic phosphite adducts of N‐allyl salts undergo a stereoselective base‐mediated aza‐Wittig rearrangement and dissociation of the chiral phosphite for overall C?H functionalization of azaarenes. This method provides efficient access to tertiary and quaternary chiral centers in isoquinoline, quinoline, and pyridine systems, tolerating a broad variety of substituents on both the allyl part and azaarenes. Catalysis with chiral phosphites is also demonstrated with synthetically useful yields and enantioselectivities.     

Enantioselective Organocatalytic Intramolecular Aza‐Diels–Alder Reaction

A highly efficient catalytic enantioselective intramolecular Povarov reaction was developed with primary anilines as 2‐azadiene precursors. A wide variety of angularly fused azacycles were obtained without column chromatography in high to excellent yields and with excellent diastereo‐ and enantioselectivity (d.r.>99:1 and up to e.r. 99:1). Furthermore, the catalyst loading could be lowered to 1 mol %, and the obtained azacycles could be used as key intermediates for further transformations to generate additional molecular diversity.     

One‐Pot Catalytic Enantioselective Synthesis of 2‐Pyrazolines

A scalable, one‐pot, enantioselective catalytic synthesis of 2‐pyrazolines from beta‐substituted enones and hydrazines is described. Pivoting on a two‐stage catalytic Michael addition/condensation strategy, the use of an aldehyde to generate a suitable hydrazone derivative of the hydrazine was found to be key for curtailing background reactivity and tuning the catalyst‐controlled enantioselectivity. The new synthetic method is easy to perform, uses a new and readily prepared cinchona‐derived bifunctional catalyst, is broad in scope, and tolerates a range of functionalities with high enantioselectivity (up to >99:1 e.r.). The significant scalability of this methodology was demonstrated with the synthesis of more than 80 grams of a pyrazoline product with 89 % catalyst recovery.