Quinazolines belong to heterocyclic chemistry, also known as 1,3-naphthalenes. The backbone consists of two six-membered aromatic rings fused to each other, with two nitrogen atoms at positions 1 and 3 on the backbone. The presence of these two nitrogen atoms in quinazoline increases its importance in pharmaceutical and biological reactions. Quinazolines and their derivatives are among the most important heterocyclic compounds due to their diverse chemical reactivity and important range of biological activities.
When the ends of the chains are joined together into a ring, cyclic compounds result; such substances often are referred to as carbocyclic or alicyclic compounds. Substitution of one or more of the ring carbon atoms in the molecules of a carbocyclic compound with a heteroatom gives a heterocyclic compound.