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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
2-Azidoaniline reacts with aromatic aldehydes to give N-(2-azidophenyl)imines which react with trimethylphosphine and then with diphenylketene to produce 6,11-dihydrobenzimidazo[1,2-b] isoquinolines in excellent yields by formal [4+2]-intramolecular cycloaddition of ketenimine with imine function of the intermediates. Benzimidazo[1,2-b]isoquinolines are obtained in good yields when 6,11-dihydrobenzimidazo[1,2-b]isoquinolines are refluxed with palladium/carbon in PhMe (Scheme 60) [24, 103–104].
Reactions of thiocarbonyl compounds with electrophilic and nucleophilic carbenes as well as with their metal complexes
Published in Journal of Sulfur Chemistry, 2020
Grzegorz Mlostoń, Heinz Heimgartner
In contrast to thiobenzophenone (25) and other aromatic thioketones, their hetaryl analogues do not react with α-diazoketones neither at standard thermal conditions nor upon LiClO4 catalysis. For that reason, the microwave irradiation was applied to support the formation of a carbene intermediate [19]. For example, the reaction of 2-diazo-1,2-diphenylethanone (azibenzil, 33) with phenyl thiophen-2-yl thioketone (34) in toluene solution, after 2 min irradiation gave a mixture of 1,3-oxathiole 35 and thietan-2-one 36 (Scheme 7). This result demonstrates the intermediacy of the carbene formed via elimination of N2 from 33, which either reacts with thioketone 34 to give a thiocarbonyl ylide or, alternatively, undergoes the Wolff rearrangement to yield diphenylketene. The latter reacts in a regioselective [2 + 2]-cycloaddition with 34 forming 36. The [2 + 2]-cycloaddition of diphenylketene with diverse hetarylthioketones, including 34, has been reported recently [20].