A pathway of desilylative activation of TMSCN as a functional isonitrile equivalent, and DABCO–THF as an appropriate system for activation in a chemoselective Strecker–Ugi type reaction, has rendered ethyl glyoxalate and various heterocyclic-2-amidines as feasible substrates, and afforded the successful synthesis of 3-amino-2-carboxyethyl substituted fused imidazoles as useful building blocks. This class of functional scaffold has provided, via construction of the fused pyrimidinone motif, the synthesis of biologically important C8–N9 annulated purines, adenines and their oxo/thio analogs. This new approach is convenient and flexible for the preparation of versatile purine-condensed heterocycles.