Facile Chemodivergent Synthesis of Fused Indolo[2,3- <i>b</i> ]quinoxalines and Benzo[4,5]imidazo[1,2- <i>c</i> ]quinazolin-6(5 <i>H</i> )-ones: An Organocatalytic Trifluoromethanesulfonic Acid-Controlled Mechanistic Switch between Condensation and R

A mild metal-free chemodivergent synthesis leading to products of two different chemotypes, such as indolo-[2,3-<i>b</i>]-quinoxalines and benzo-[4,5]-imidazo-[1,2-<i>c</i>]-quinazolin-6-(5<i>H</i>)-ones, has been described from common starting materials, isatin and 1,2-diaminobenzene, at room temperature in an environmentally benign EtOH solvent. The EtOH mediated condensation between isatin and 1,2-diaminobenzene delivers exclusively fused indolo-[2,3-<i>b</i>]-quinoxalines in good/excellent yields (65-89%) in 8 h, and catalytic protic acid (CF₃SO₃H) in EtOH furnishes N-fused benzo-[4,5]-imidazo-[1,2-<i>c</i>]-quinazolin-6-(5<i>H</i>)-ones selectively in good/excellent yields (66-88%) in 2 h via rearrangement of the isatin core following C2-C3 bond cleavage and N-atom insertion with 1,2-diaminobenzene. Thus, the switch selectivity between benzo-[4,5]-imidazo-[1,2-<i>c</i>]-quinazolin-6-(5<i>H</i>)-ones and indolo-[2,3-<i>b</i>]-quinoxalines could be finely programmed with the presence/absence of catalytic CF₃SO₃H induced by an ionic vs non-ionic pathway. A wide array of starting materials housing structural and electronic variations (e.g., electronically neutral, moderate/strong electron-donating, moderate electron-attracting functionalities, and heteroarene) allows the scope of diversity creation and provides facile access to molecular libraries with elaborate, well-decorated structures. The operational simplicity, ease of product purification (in the case of indolo-[2,3-<i>b</i>]-quinoxalines) by precipitation/filtration, recyclability of catalytic CF₃SO₃H, and a high degree of chemoselectivity through decisive cleavage of the C2-C3 bond over other labile bonds under protic acid catalysis signify distinct advantages of developed protocols. The late-stage synthetic manipulation at the free-NH site of final products and a "gram-scale" preparation further demonstrate the promising usefulness of chemodivergent synthesis.