Nucleophilic and Electrophilic Properties of Carbenes,II. 4-Biphenylyl-4-pyridylcarbene |
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Authors: | Nguy M
ng Ln Curt Wentrup |
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Institution: | Nguyňñ Mǒng Lán,Curt Wentrup |
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Abstract: | Flash pyrolysis of 4-biphenylyl-4-pyridyldiazomethane ( 4 gave 7-phenyl-2-azafluorene) 5 , which was also synthesized from 3-mesitoylpyridine in four steps. 4-Biphenylyl-4-pyridyl-13C]-diazomethane ( 9 ) was prepared from isonicotinic 13C]-acid chloride in three steps. Flash pyrolysis of 9 established that 4a- and 4b-13C]-7-phenyl-2-azafluorenes are formed in a carbene-carbene rearrangement in which ring expansion of the biphenyl part dominates over that of the pyridine ring. These results support the postulate that carbene-carbene rearrangements are favoured by a nucleophilic interaction between the filled singlet carbene sp2 (σ) orbital and the lowest unoccupied molecular orbital (LUMO) of the aromatic ring. |
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