C15H10 and C15H12 Thermal Chemistry: Phenanthrylcarbene Isomers and Phenylindenes by Falling Solid Flash Vacuum Pyrolysis of Tetrazoles

Abstract

2-Phenyl-5-(phenylethynyl)tetrazole 44 provides a new entry to the C15H10 energy surface. Flash vacuum pyrolysis of 44 using the falling solid flash vacuum pyrolysis (FS-FVP) method afforded cyclopenta[def]phenanthrene 31 and cyclopenta[jk]fluorene 52 as the principal products. The products are explained in terms of the formation of N-phenyl-C-phenylethynylnitrile imine/(phenylazo)(phenylethynyl)carbene 45 and its cyclization to 3-(phenylethynyl)-3H-indazole 46b. Pyrolytic loss of N2 from 46b generates C15H10 intermediate 48. Cyclization of 48 to a dibenzocycloheptatetraene derivative and further rearrangements with analogies in the chemistry of phenylcarbene and the naphthylcarbenes leads to the final products. Similar pyrolysis of 2-phenyl-5-styryltetrazole 43 afforded 3-styrylindazole 58, which on further pyrolysis eliminated N2 to generate 3- and 2-phenylindenes 61 and 62 via C15H12 intermediates.