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This article shows that two extremely important families of fused heterocyclic assemblies, namely 6-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine and 5a-methyl-5a,6-dihydro-5H,12H-benzo[4,5]imidazo[1,2-a]pyrrolo[1,2-d]pyrazine, can be synthesized from only two available building blocks (N-allenylpyrrole-2-carbaldehyde and o-phenylenediamine) by controlling only one reaction parameter (water content of the medium). It should be emphasized that the latter class of compounds (with an a/d arrangement) is previously unknown. If the allene group is introduced not into the starting compound, but during the reaction (in superbase media), a heterocyclic ensemble, 5-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazines, with a different position of the methyl group is formed.

The effect of substituents in the pyrrole ring and at the triple bond on the formation of fused pyrrolooxazines from 1H‐pyrrol‐2‐ylmethanols and propargyl chlorides has been theoretically and experimentally studied. The energy characteristics of the reaction are evaluated using quantum‐chemical calculations (CBS‐Q//B3). A one‐pot transition metal‐free synthesis of substituted 3‐methyl‐1H‐pyrrolo[2,1‐c][1,4]oxazines in good yields has been implemented in the superbasic system NaOH/DMSO.