Direct observation of a carbene-pyridine ylide by matrix IR spectroscopy.: Rearrangements of 2-pyridylacylcarbenes

FVT of 2-(2-diazoacetyl)pyridine (1) yields 2-pyridylketene (3) (largely in the s-Z form 32), which dimerizes to quinazolinone 5. Matrix photolysis of 1 (largely in the EZ form 1EZ) yields the carbene-pyridine ylide 6, which on further photolysis at lambda > 320 nm is converted to (mainly) the s-E ketene 3E. Continued photolysis of 3E at 320 nm converts it to 3Z, and this process is reversed on photolysis at 254 nm.