Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

C4-aldehyde of guaiazulene: synthesis and derivatisation

Guaiazulene is an alkyl-substituted azulene available from natural sources and is a much lower cost starting material for the synthesis of azulene derivatives than azulene itself. Here we report an approach for the selective functionalisation of guaiazulene which takes advantage of the acidity of the protons on the guaiazulene C4 methyl group. The aldehyde produced by this approach constitutes a building block for the construction of azulenes substituted on the seven-membered ring. Derivatives of this aldehyde synthesised by alkenylation, reduction and condensation are reported, and the halochromic properties of a subset of these derivatives have been studied.

Azulenium chemistry: towards new derivatives of photochromic dihydroazulenes

The reactivity of azulenium salts, derived from photochromic dihydroazulenes (DHAs), towards a nucleophile is reported, and one regioisomer product is tautomerised into a new photochromic DHA that undergoes a ring-opening to a vinylheptafulvene (VHF).