Reaction of functionalized maleimides with versatile nucleophiles. Synthesis, electronic spectra and molecular orbital study

This article comprehensively describes the condensation reactions of functionalized maleimides (3-methylthio-2,5-dioxo-1H-pyrroles) with some nucleophilic reagents to afford a series of novel heterocycles, as briefly reported in a previous communication [Tominaga Y, Komiya K, Itonaga S, Yoshioka N, Kataoka S, Sasaki K, et al. Heterocycles 1997;46:41]. The reactions of the functionalized maleimides (5a–c) with N,N-dialkylanilines (6a–d) smoothly proceeded to give the corresponding 3-(4-dialkylamino)phenyl-1-methyl-1H-pyrrole-2,5-diones (7a–i). Cyclic products, the 2H,4H-[1]benzopyrano[3,4-c]pyrrole-1,3,4-triones (10a–c, 12, 13) were also obtained within the same reaction framework, using 3-dialkylaminophenols (6g–j) and resorcinol (6k) as the nucleophilic reagents. Further treatments of (7a,b,h) with Lawesson's reagent afforded the brilliant blue mono-thiocarbonyls, 4-(4-dialkylamino)phenyl-3-cyano-1-methyl-5-oxo-pyrrole-2-thiones (9a–c). The UV/vis spectral characteristics of the new heterocycles, particularly of the controversial aromatic mono-thiocarbonyl compounds (9a–c), were computationally analyzed by means of semi-empirical and Time Dependent Density Functional Theory (TDDFT) quantum chemistry calculations.