A Three-Component Reaction Based on a Remote-Group-Directed Dynamic Kinetic Aza-Michael Addition: Stereoselective Synthesis of Imidazolidin-4-ones

Synthesis of Polycyclic Imidazolidinones via Cascade [3 + 2]-Annulation of β-Oxo-acrylamides with Cyclic N-Sulfonyl Imines

An Et3N-catalyzed cascade [3 + 2]-annulation of β-oxo-acrylamides with cyclic N-sulfonyl ketimines or sulfamate-derived imines is developed under mild reaction conditions, which provides a concise and efficient route to access valuable sultam- or sulfamidate-fused imidazolidinone derivatives in good to excellent yields (80-95% yields) with excellent diastereoselectivities (>20:1 drs). The current protocol features atom economy, a transition-metal-free process, and broad functional group tolerance. Moreover, the asymmetric variant of the [3 + 2]-cycloaddition reaction was achieved in the presence of diphenylethanediamine or quinine-based bifunctional squaramide organocatalysts C-1 and C-11, giving the corresponding chiral polycyclic imidazolidinones in 68-90% yields with 25-94% ees and >20:1 drs in all cases.

Crystal structure, Hirshfeld surface analysis and PIXEL calculations of a 1:1 epimeric mixture of 3-[(4-nitro-benzyl-idene)amino]-2(R,S)-(4-nitro-phenyl)-5(S)-(propan-2-yl)imidazolidin-4-one

A 1:1 epimeric mixture of 3-[(4-nitro-benzyl-idene)amino]-2(R,S)-(4-nitro-phen-yl)-5(S)-(propan-2-yl)imidazolidin-4-one, C19H19N5O5, was isolated from a reaction mixture of 2(S)-amino-3-methyl-1-oxo-butane-hydrazine and 4-nitro-benz-alde-hyde in ethanol. The product was derived from an initial reaction of 2(S)-amino-3-methyl-1-oxo-butane-hydrazine at its hydrazine group to provide a 4-nitro-benzyl-idene derivative, followed by a cyclization reaction with another mol-ecule of 4-nitro-benzaldehyde to form the chiral five-membered imidazolidin-4-one ring. The formation of the five-membered imidazolidin-4-one ring occurred with retention of the configuration at the 5-position, but with racemization at the 2-position. In the crystal, N-H⋯O(nitro) hydrogen bonds, weak C-H⋯O(carbon-yl) and C-H⋯O(nitro) hydrogen bonds, as well as C-H⋯π, N-H⋯π and π-π inter-actions, are present. These combine to generate a three-dimensional array. Hirshfeld surface analysis and PIXEL calculations are also reported.

Recent developments in asymmetric multicomponent reactions

Multicomponent reactions (MCRs) receive increasing attention because they address both diversity and complexity in organic synthesis. Thus, in principle diverse sets of relatively complex structures can be generated from simple starting materials in a single reaction step. The ever increasing need for optically pure compounds for pharmaceutical and agricultural applications as well as for catalysis promotes the development of asymmetric multicomponent reactions. In recent years, asymmetric multicomponent reactions have been applied to the total synthesis of various enantiopure natural products and commercial drugs, reducing the number of required reaction steps significantly. Although many developments in diastereoselective MCRs have been reported, the field of catalytic enantioselective MCRs has just started to blossom. This critical review describes developments in both diastereoselective and catalytic enantioselective multicomponent reactions since 2004. Significantly broadened scopes, new techniques, more environmentally benign methods and entirely novel MCRs reflect the increasingly inventive paths that synthetic chemist follow in this field. Until recently, enantioselective transition metal-catalyzed MCRs represented the majority of catalytic enantioselective MCRs. However, metal contamination is highly undesirable for drug synthesis. The emergence of organocatalysis greatly influences the quest for new asymmetric MCRs.