Stereodiversified Modular Synthesis of Non-planar Five-Membered Cyclic N -Hydroxylamidines: Reactivity Study and Application to the Synthesis of Cyclic Amidines

Doubly stereoconvergent crystallization enabled by asymmetric catalysis

Synthetic methods that enable simultaneous control over multiple stereogenic centers are desirable for the efficient preparation of pharmaceutical compounds. Herein, we report the discovery and development of a catalyst-mediated asymmetric Michael addition/crystallization-induced diastereomer transformation of broad scope. The sequence controls three stereogenic centers, two of which are stereochemically labile. The configurational instability of 1,3-dicarbonyls and nitroalkanes, typically considered a liability in stereoselective synthesis, is productively leveraged by merging enantioselective Brønsted base organocatalysis and thermodynamic stereocontrol using a single convergent crystallization. The synthesis of useful γ-nitro β-keto amides containing three contiguous stereogenic centers is thus achieved from Michael acceptors containing two prochiral centers.

Diastereoselective Synthesis of Functionalized 5-Amino-3,4-Dihydro-2H-Pyrrole-2-Carboxylic Acid Esters: One-Pot Approach Using Commercially Available Compounds and Benign Solvents

A novel three-step four-transformation approach to highly functionalized 5-amino-3,4-dihydro-2H-pyrrole-2-carboxylic acid esters, starting from commercially available phenylsulfonylacetonitrile, aldehydes, and N-(diphenylmethylene)glycine tert-butyl ester, was developed. The one-pot strategy delivered this class of amidines bearing, for the first time, three contiguous stereocenters, in good to high yield and diastereoselectivity. The entire sequence was carried out using diethyl carbonate and 2-methyl tetrahydrofuran as benign solvents, operating under metal-free conditions. The process could be conveniently scaled-up, and the synthetic utility of the products was demonstrated.

Production of Amidinyl Radicals via UV-Vis-Light Promoted Reduction of N-Arylthiophene-2-carboxamidoximes and Application to the Preparation of Some New N-Arylthiophene-2-carboxamidines

A modern method for the preparation of some new N-arylthiophene-2-carboxamidines via amidinyl radicals generated using UV-vis-light promoting the reduction of N-arylthiophene-2-carboxamidoximes without any catalyst in a short amount of time, highly straight forward, and in an efficient manner is described. This method defeats the flaws of the conventional methods for the reduction of amidoxime derivatives to amidine derivatives, which require harsh conditions such as using a strong acid, high temperature, and expensive catalysts. Benzo[d]imidazoles, benzo[d]oxazoles, and amides can also be synthesized by applying this method. The photoproducts were analyzed by various spectroscopic and analytical techniques, including thin-layer chromatography, column chromatography, high-performance liquid chromatography, gas chromatography/mass spectrometry, IR, ¹H NMR, ¹³C NMR, and MS. Notably, the chromatographic analyses proved that the best time for the production of N-arylthiophene-2-carboxamidines is 20 min. The reaction mechanism comprising pathways and intermediates was also suggested via the homolysis of N-O and C-N bonds.

Silver oxide mediated novel SET oxidative cyclization: stereoselective synthesis of 3-azabicyclo[n.1.0]alkanes

Stereoselective synthesis of 3-azabicyclo[n.1.0]alkane by silver oxide catalyzed SET oxidative cyclization.