ABSTRACT
The importance of asymmetric organocatalysis in contemporary organic synthesis is widely acknowledged. However, there are practically no data on the environmental safety of organocatalysts, although this aspect is crucial for the sustainability of all new materials, chemicals, and technologies. To start to fill this data-gap, a library of 26 organocatalysts containing hydrogen-bonding catalysts [(thio)ureas and squaramides] and aminocatalysts (primary or secondary amines) was evaluated for their toxicity using the naturally luminescent Vibrio fischeri bacteria (ISO assay; one of the most widely used ecotoxicity tests). Thioureas and squaramides were shown to be relatively toxic: none of them was ranked as "not harmful" (i. e., half maximal effective concentration EC50 >100â mg L-1 ), whereas the presence of the trifluoromethyl moiety increased their toxic effect. Importantly, the aminocatalysts, whose EC50 values ranged from 25 to >300â mg L-1 , could be considered remarkably more environmentally safe or green alternatives.
Subject(s)
Thiourea , Urea , Catalysis , Hydrogen , Hydrogen BondingABSTRACT
An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied in the presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities.