Synthesis and Catalytic Activity of 1,2-Benzenediamine-Derived Organocatalysts Based on (1<i>R</i>,2<i>R</i>)-Cyclohexane-1,2-Diamine

Abstract

A four-step synthesis process of bifunctional, noncovalent organocatalysts based on the chiral (1R,2R)-cyclohexane-1,2-diamine scaffold containing a 1,2-benzenediamine H-bond donor was developed. Nucleophilic aromatic substitution of the 2-fluoronitrobenzene derivative with the commercial (1R,2R)-cyclohexane-1,2-diamine was followed by selective alkylation of the primary amino group, reduction of the aromatic nitro group and final derivatization of the primary aromatic amino group, i.e., acylation, sulfonation, reductive alkylation and arylation, leading to the four subtypes of organocatalysts. All new compounds were fully characterized. The prepared organocatalysts (32 examples) were tested in the Michael addition of acetylacetone to trans-β-nitrostyrene, yielding the addition product with incomplete conversions (up to 93%) and enantioselectivities of up to 41% ee.

Keywords

• asymmetric organocatalysis
• H-bond donor organocatalysts
• (1<i>R</i>,2<i>R</i>)-cyclohexane-1,2-diamine
• benzene-1,2-diamines
• reduction
• nucleophilic aromatic substitution