One-step construction of complex polyheterocycles via a sequential post-GBB cyclization/spiro ring expansion triggered by a [1,5]-hydride shift

Abstract

An efficient tandem route to novel amino-indazolo[3′,2′:2,3]imidazo[1,5-c]quinazolin-6(5H)-ones has been explored. The reaction proceeds via a cascade involving an Ugi-variant Groebke–Blackburn–Bienayme (GBB) reaction that occurs through the in situ generation of a spirocyclic intermediate, which undergoes sequential ring opening via a [1,5]-hydride shift followed by an intramolecular nucleophilic reaction of the newly generated isocyanate to furnish complex polyheterocyclic frameworks. The main advantages of this protocol include short reaction time, excellent yield, easy work-up, operational simplicity and the absence of extraction and chromatographic purification steps.