The C₆H₅N energy surface. III. Isomerization processes and intramolecular trapping in picolylcarbenes

Abstract

The synthesis is reported of a series of 5-(methyl-2-, -3- and -4- pyridyl)tetrazoles from the corresponding picolinecarbonitriles. These compounds are used as gas phase generators for the corresponding picolylcarbenes at 600°/0.05 mm. The normal isomerization process in arylcarbenes are interrupted in some cases by intramolecular trapping by the methyl groups, resulting in the first reported syntheses of cyclobuta-[b] and -[c]pyridines. The major process competing with this is that of nitrogen-extrusion to give tolylnitrenes, which then undergo ring contraction to form methyl-cyclopentadienecarbonitriles. The relative yields from these and other processes are used to deduce the preferred isomerization pathways in picolylcarbenes. In methyl-2- pyridylcarbenes there is almost exclusive insertion into the 2,3-bond, leading to the tolylnitrenes. The 3- and 4-pyridylcarbenes, however, show a tendency for the carbene centre to oscillate over the 3-, 4- and 5-positions of the ring with slower leakage to the 2-position.