ABSTRACT
A series of bifunctional phase-transfer catalysts (PTCs) were synthesized to catalyze the [3 + 2] coupling reaction of isocyanates and epoxides to afford 2-oxazolidinones in good to high yields (up to 92% yield) using PhCl as a solvent at 100 °C within 12 h. These bifunctional PTCs were easily prepared from commercially available tertiary-primary diamines and isocyanates (or isothiocyanates, mono-squaramides, respectively) in two simple steps with good modularity and demonstrated high efficiency (2.5 mol% catalyst-loading). The synergistic interaction of the quaternary ammonium salt center and hydrogen-bond donor group in the catalyst with the substrate is crucial to this atom-economic reaction.
ABSTRACT
A one-pot, base-catalyzed, tandem grinding process involving carrying out aldol condensation and Michael addition in sequence to produce 3,4,5-trisubstituted isoxazoles from 3,5-dimethyl-4-nitroisoxazole, aromatic aldehydes and activated methylene compounds has been developed. In the presence of 10 mol% of pyrrolidine, aldol condensations of 3,5-dimethyl-4-nitroisoxazole with various aromatic aldehydes were performed with 3-10 minutes of grinding to provide 5-styryl-3-methyl-4-nitroisoxazoles in good to quantitative yields without further purification. Then, Michael additions between 5-styryl-3-methyl-4-nitroisoxazoles and activated methylene compounds (including ethyl 2-nitroacetate and alkyl 2-cyanoacetates) were carried out in the presence of 10 mol% of Et3N in the same mortar with 3-5 minutes of continuous grinding to produce 3,4,5-trisubstituted isoxazoles in good to excellent yields.
ABSTRACT
AIM AND OBJECTIVE: The direct ß-functionalization of trans-ß-nitroolefins by Michael reaction is regarded as an efficient way to provide precursors for ß-functional amines. However, Michael additions by grinding means with solvent-free conditons are rarely reported. We have developed facile access to ß-functional nitroalkanes by grinding means under solvent-free conditions. MATERIALS AND METHODS: From commercially available materials including ethyl 2-nitroacetate, alkyl 2-cyanoacetates and malononitrile, the grinding reactions between these above-mentioned activated methylenecompounds and various trans-ß-nitroolefins were performed at room temperature and solvent-free conditions. RESULTS: A highly efficient direct Michael reaction of nitroolefins by simple grinding means has been developed. Various trans-nitrostyrenes were easily converted into corresponding ß-functional nitroalkanes in excellent yields within 5~10 min (up to 36 examples). CONCLUSION: Herein, we have developed a simple and efficient way to ß-functional nitroalkanes through Michael reactions by grinding means. The grinding Michael reaction is fast, clean and stable and these Michael adducts could be easily converted into the other amino compounds served as building blocks in organic synthesis.
