Bicyclic Form Research Articles

The chemistry of 4‐hydrazino‐7‐phenylpyrazolo[1,5‐a] ‐1,3,5‐triazines

AbstractThe reaction of 4‐hydrazino‐7‐phenylpyrazolo[1,5‐a]‐1,3,5‐triazine (4) with nitrous acid gave 8‐phenyltetrazolo[1,5‐e]pyrazolo[1,5‐a]‐1,3,5‐triazine (5b), which was determined by pmr and ir spectra to be in equilibrium with 4‐azido‐7‐phenylpyrazolo[1,5‐a]‐1,3,5‐triazine (5a). The equilibrium between the tetrazolo (5b) and azido (5a) forms was studied by pmr and an attempt was made to determine if substituents in the pyrazole nucleus could sufficiently stabilize the tricyclic tetrazolo form (5b) over the bicyclic azido form (5a). Thermal degradation of 5(a ⇌ b) in an aprotic solvent gave 4‐amino‐7‐phenylpyrazolo[1,5‐a]‐1,3,5‐triazine (7), indicating the probability of a nitrene mechanism involved in the decomposition. Heating 5 in aqueous base gave both 7 and the “hydroxy” analog, 7‐phenylpyrazolo[1,5‐a]‐1,3,5‐triazin‐4(3H)one (6), further substantiating the existence of a nitrene intermediate with a competing nucleophilic displacement of the azido group by a hydroxyl group. Cyclization of 4 with diethoxymethylacetate (DEMA) gave 8‐phenyl‐s‐triazolo[4,3‐e]pyrazolo[1,5‐a]‐1,3,5‐triazine (8), which underwent thermal rearrangement to 8‐phenyl‐s‐triazolo[2,3‐e]pyrazolo[1,5‐a]‐1,3,5‐triazine (9). Acid catalyzed ring opening of 9 with formic acid gave 3‐N‐formamido‐5‐phenyl‐2(2‐s‐triazolyl)pyrazole (10). The failure of 10 to recyclize to 9 with the resultant loss of water, supported the theory that the rearrangement of 8 to 9 might occur simply as a concerted, thermally induced “anhydrous” rearrangement rather than via a covalently hydrated intermediate or a Dimroth type mechanism (in the base catalyzed rearrangement).

Nomenclature of quinones with isoprenoid side-chains recommendations (1973)

Four tocopherol model compounds, the chroman-6-ols (1–4) having the typical substitution pattern of α-, β-, γ-, and δ-tocopherol (vitamin E), were oxidized to the corresponding para-quinones (5–8), and dehydrogenated to the 2H-chromen-6-ols (17–20) involving initial acetyl protection of the phenolic OH and deprotection as the last step. The chromenols were also converted into the para-quinones (21–24), which existed in the bicyclic hemiketal form, in contrast to the chromanol-derived, monocyclic quinones 5–8, the ketalization behavior agreeing well with computations on the DFT level.

The tautomerism of N-methyl-2-phenacylthioimidazoline

N-Methyl-2-phenacylthioimidazoline (2) and the corresponding hydrobromide (1) exist largely in bicyclic forms owing to interactions between the carbonyl group and a ring nitrogen atom.