Synthesis and Photochemistry of 5,7-Bis(diazo)-1,2,3,4-dibenzocyclohepta-1,3-dien-6-one. Generation and Reactions of Phenanthrenodiazacyclopentadiene, Phenanthrenocyclopropenone, and 9,10-Phenanthryne

Article abstract of DOI:10.1021/jo00113a011

The title compound 15 was prepared as the first 1,3-bis(diazo) ketone incorporated into a seven-membered ring, and its photochemical pathways were investigated not only by product analysis study but also by using matrix isolation spectroscopy.Irradiation of 15 in alcoholic solvents gave 9-(alkoxycarbonyl)phenanthrene 16 as a main product, while similar irradiation in non-nucleophilic solvents provided diphenanthreno-syn-1,5-diazabicyclo<3.3.0>octadienedione (20).The formation of these products is interpreted as indicating that 15 eliminates one of two diazo functions upon photoexcitation to form 9-diazo-10-carbonylphenanthrene (21) which either reacts with alcohol by eliminating the second dinitrogen, leading to 16, or undergoes dimerization to form 20.Photolysis of 15 in an ethanol matrix at 77 K gave 9-ethoxyphenanthrene (31) as a new product along with 16.Irradiation of 15, matrix-isolated in Ar at 10 K monitored by IR, indicated that phenanthrenocyclopropenone (28) was formed as an initial product which then underwent photodecarbonylation to leave 9,10-phenanthryne (32), and that 32 reacted with CO to reproduce 28 upon photoexcitation.The cyclopropenone (28) was shown to be generated also by photolysis of 9,10-dicarboxyphenanthrene anhydride (33) in Ar matrix at 10 K.A plausible mechanism to explain the observed sequential decomposition of the two diazo functions in the room temperature photolytic run and the formal simultaneous elimination of two dinitrogens in the low temperature matrix run is proposed.