A stereoselective route to 3-methyl-2-methylsulfanyl-5-ylidene-3,5-dihydroimidazol-4-one derivatives and precursor of Leucettamine B

A range of aromatic aldehydes 8a-f was tested in Knoevenagel reaction with 3-methyl-2-methylsulfanyl-3,5-dihydroimidazol-4-one 7 and piperidine as catalyst using solvent-free conditions under microwave-mediated conditions. The results of these condensations were compared to classical procedure in methylene chloride. This efficient, simple and environmentally friendly methodology gave respectively and stereoselectively the (5Z)-5-arylidene-3,5-dihydroimidazol-4-ones 9a-e in good yields (78-95%) and the precursor 9f of Leucettamine B. Then, these solvent-less condition reactions have been also applied to cyclic ketones 10a-d, acetone 12a and actived ketones 12b,c. The H-1, C-13 NMR spectrum of some representative 5-ylidene-3,5-dihydroimidazol-4-ones are also reported.