Azulenylcarbene and Naphthylcarbene Isomerizations. Falling Solid Flash Vacuum Pyrolysis

David Kvaskoff, Jürgen Becker, Curt Wentrup

1-Azulenylcarbene 18 has been generated from 5-(1-azulenyl)tetrazole and the sodium salt of azulene-1-carbaldehyde tosylhydrazone using the falling solid flash vacuum pyrolysis (FS-FVP) method. The principal products, which are also formed from both 1- and 2-naphthylcarbenes, cyclobuta[de]naphthalene 6, cyclopenta[cd]indene 16, and benzofulvenallene 17, are explained in terms of two reaction paths, (a) a rearrangement to benzofulvenyl-7-carbene 13, and (b) a rearrangement to 1-naphthylcarbene 1. Moreover, 16 is also formed from 2-azulenylcarbene 30, thereby indicating the occurrence of a 2-azulenylcarbene - 1-azulenylcarbene rearrangement. The reaction mechanisms are supported by DFT calculations at the B3LYP/6-31G** level, which indicate that all the rearrangements have activation barriers below 35 kcal/mol, thus making them readily achievable under FVP conditions.