Dimroth Rearrangement: Translocation of Heteroatoms in Heterocyclic Rings and Its Role in Ring Transformations of Heterocycles

An approach to novel fused triazole or tetrazole derivatives starting from benzimidazo[1,2‐a]quinazoline‐5(7H)‐one and 5,7‐dihydro‐5‐oxopyrido[3′,2′:5,6]pyrimido[1,2‐a]benzimidazole

“…The former showed the triazole methyl as a singlet at 3.06 ppm; the latter exhibited two methyl singlets: one at 2.61 ppm, the other at 3.06 ppm. In agreement with literature reports on fused 1,2,4-triazoles [8], the methyl protons at 2.61 ppm could be assigned to the isomer 8 b, as the methyl groups in the rearranged products are more upfield than the corresponding ones in the unrearranged compounds.…”

A new convenient synthesis of 2,4‐disubstituted‐1,2,4‐triazolo[1,5‐a] quinazolin‐5(4H)‐ones

“…The conversion of 3 into 5 is reminiscent of other related oxidative cyclization of aldehyde N-heteroarylhydrazones with iron(III) chloride, which was reported to proceed via generation of the respective nitrilimines 4 which undergo in situ 1,5-electrocyclization to give the respective fused heterocycles [11,12] (Scheme 1). Vol 45 [15]. To account for the rearrangement of 5 into 6, it is suggested that it occurs through ring opening and ring closure as depicted in Scheme 2.…”

Synthesis of some novel pyrazolo[3,4-d]pyrimidine derivatives

“…We are therefore led to propose structures 5 for the hydrazine form and 6 for the azo form; the rearrangement of 4 to 5 could be due to Dimroth rearrangement. 11,12 Mass spectrometry confirmed the molecular weight of compounds 6. The structure of compound 4 was excluded based on NMR data.…”