A STUDY OF THE VACUUM PYROLYSIS OF 4-DIAZO-3-ISOCHROMANONE WITH HEL ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY

A newly developed ultraviolet photoelectron spectrometer - CO2 laser i nstrument that utilizes a 50-W CW laser as a directed heat source was used to study the vacuum pyrolysis of 4-diazo-3-isochromanone (1). Ana lysis of the pyrolysate with ultraviolet photoelectron spectroscopy an d photoionization mass spectrometry established that 1 undergoes a fac ile, unexpected pyrolysis at a laser power level of 26 W yielding N-2, CO, and benzocyclobutenone (6). A multistep mechanism beginning with the formation of 4-carbena-3-isochromanone (2), which rearranges to ox aketene 3, can be written for the reaction. If 3 is an intermediate, i t must be unusually thermally labile for it readily decarbonylates to 2-carbena-3,4-benzotetrahydrofuran (4). The ring opening of 4 into the ortho-quininoid ketene 5 and the cyclization of 5 into 6 are possible final steps in the conversion of 1 into 6.