New efficient synthesis of imidazo[2,1-b]quinazoline-2,5(1H,3H)-diones via a consecutive aza-Wittig/heterocumulene-mediated annulation

Abstract

The carbodiimide 2, obtained from aza-Wittig reaction of iminophosphorane 1 with aromatic isocyanate, reacted with α-amino ester in the presence of triethylamine to give imidazo[2,1-b]quinazoline-2,5(1H,3H)-diones 5 (when R 2 is H) or quinazolinones 6 (when R 2 is not H).Imidazo[2,1-b]quinazoline-2,5(1H,3H)-diones 5 were prepared more generally by another route, using a consecutive aza-Wittig / heterocumulene-mediated annulation of iminophosphoranes 9 with isocyanates and catalytic sodium ethoxide.

RE[N(SiMe3)2]3-Catalyzed Guanylation/Cyclization of Amino Acid Esters and Carbodiimides

“…Only one example was found to yield the target quinazolinones from isatoic anhydride without any catalyst . Utilizing the aza-Wittig reaction of iminophosphorane with heterocumulene on solid phase, for the synthesis of 2-amino-substituted 3 H -quinazoline-4-one, usually begins with isatoic anhydride as well . Because of the commercially available or readily generated isatoic anhydride, which gives rise to differently substituted quinazolinone skeletons, strategies based on isatoic anhydride are popular.…”