Nucleophilic and Electrophilic Properties of Carbenes, II. 4‐Biphenylyl‐4‐pyridylcarbene
- 1 January 1976
- journal article
- research article
- Published by Wiley in Helvetica Chimica Acta
- Vol. 59 (6) , 2068-2073
- https://doi.org/10.1002/hlca.19760590620
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.Keywords
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