Thermal fragmentation and rearrangement of some N-phenylbenzamide oxime dervatives II. Synthesis of benzimidazoles

Investigation of Thermolysis Products of Some N‐Arylthiophene‐2‐carboxamidoximes by Analytical and Spectroscopic Analyses

“…The N ‐arylthiophene‐2‐iminyl derivatives may abstract hydrogen radical from the reaction mixture to form N ‐2‐thenylidene aniline derivatives ( 4 a‐d ) in low yield up to 3.3%, m/e 187, 221, 201 and 217 successively and are easily identified from GC/MS and fragmentation pattern. The interaction between N ‐arylthiophene‐2‐iminyl derivatives and hydroxyl radical formed N ‐arylthiophene‐2‐carboxamides ( 5 a‐d ) with high yield up to 50%, m/e 203, 237, 217 and 233, respectively . A possible pathway for the formation of 2‐(thiophene‐2‐yl)benzo[d]oxazoles ( 6 a‐d ) in low yield up to 3.7%, m/e 201, 235, 215 and 231, respectively through a process of tautomeric from keto to enol form followed by intramolecular cyclization of N ‐arylthiophene‐2‐carboxamidyl derivatives ( 5 a‐d ) .…”

“…Scheme 2. Suggested mechanism for formation thiophene-2-carbonitrile (2), arylamines (3a-d) and 2,4,6-tri(thiophene-2-yl)-1,3,5-triazine (12). Scheme 4.…”

“…[11] The arylamines (3d and 3e) were produced in high yield 18% and 24%, respectively according to the formation of these compounds through two both i. e. two Schemes (2 and 4). Thiophene-2-carbonitrile (2) which readily available in the reaction medium was undergone cyclotrimerization to form 2,4,6-tri(thiophene-2-yl)-1,3,5-triazine (12) m/e 327, [25] (Scheme 2, Table 1).…”

“…The interaction between N-arylthiophene-2iminyl derivatives and hydroxyl radical formed N-arylthiophene-2-carboxamides ( 5 a-d) with high yield up to 50%, m/e 203, 237, 217 and 233, respectively. [12] A possible pathway for the formation of 2-(thiophene-2-yl)benzo[d]oxazoles (6 a-d) in low yield up to 3.7%, m/e 201, 235, 215 and 231, respectively through a process of tautomeric from keto to enol form followed by intramolecular cyclization of N-arylthiophene-2carboxamidyl derivatives (5 a-d). [26] The mechanism for formation of 2-(thiophene-2-yl)benzo[d]oxazoles (6 a-d) was proved by the thermolysis of N-phenylthiophene-2-carboxamide (5 a) under the same conditions of the thermolysis of target compounds (a-d) (Scheme 3), see below Table 1.…”

“…The scientists detected that as early as 1956, benzamidoxime was heated only at 170 °C and carefully examined the products by Italian workers, they reported the separation of benzonitrile, benzamide, 2,5‐diphenyl‐1,3,4‐triazole,3,5‐diphenyl‐1,2,4‐oxadiazole and 2,4,6‐triphenyltriazine as well as four gaseous products, nitrogen, nitrogen oxide, ammonia and water . In our research group we reported the flash vacuum pyrolysis (FVP) of N ‐phenylbe nzamidoxime, thermal fragmentation of N ‐arylbenzamidoxime and O ‐phenylsulfonyloxime derivatives, thermal fragmentation and rearrangement of N ‐arylbenzamidoximes, thermal fragmentation and rearrangement of N ‐aryl‐2‐furamidoximes and thermolysis of N ‐arylnicotinamidoximes . Recently, we have reported the thermolysis of N ‐arylbenzamidoximes (Ar=pyridyl and α‐napthyl) in presence of radical scavenger as tetralin gave anilides and imidazoles as the major products in addition to phenols, arylamines, benzonitrile, triphenyl triazine and oxazole derivatives besides 1‐hydroxytetralin, α‐tetralone and 1,1′‐bitetrayl .…”