Preparation and Structures of New Azobenzene Derivatives with a 3-Guaiazulenylvinyl Group

Abstract

Abstract Wittig reactions of (E)-4-(4-methoxyphenyldiazenyl)benzaldehyde and (E)-4-[4-(dimethylamino)phenyldiazenyl]benzaldehyde with (3-guaiazulenylmethyl)triphenylphosphonium bromide in ethanol in the presence of sodium ethoxide at 25 °C for 24 h under argon give only E forms (E)-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}methoxybenzene and (E)-N,N-dimethyl-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}aniline in 71 and 73% yields. Comparative studies on spectroscopic properties and crystal structures of the two new extended π-electron systems with those of structurally related (and delocalized) π-electron systems (3-guaiazulenyl)[(E)-4-(4-methoxyphenyldiazenyl)phenyl]methylium ion and {(E)-4-[4-(dimethylamino)phenyldiazenyl]phenyl}(3-guaiazulenyl)methylium ion compounds are reported. Similarly, Wittig reaction of (E)-diphenyldiazene-4,4′-dicarbaldehyde with the same reagent under the same reaction conditions as the above affords only E forms (E)-4-{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyldiazenyl}benzaldehyde and (E)-bis{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyl}diazene in 7 and 24% yields. Furthermore, reaction of guaiazulene (=7-isopropyl-1,4-dimethylazulene) with (E)-diphenyldiazene-4,4′-dicarbaldehyde in methanol in the presence of hexafluorophosphoric acid at 25 °C for 30 min provides (E)-diphenyldiazene-4,4′-bis(3-guaiazulenylmethylium) bis(hexafluorophosphate) in 46% yield which upon reduction with NaBH4 in a mixed solvent of ethanol and acetonitrile at 25 °C for 30 min gives (E)-bis[4-(3-guaiazulenylmethyl)phenyl]diazene in 88% yield. Comparative studies of spectroscopic properties of a new extended π-electron system (E)-bis{(E)-4-[2-(3-guaiazulenyl)vinyl]phenyl}diazene with those of a new delocalized π-electron system (E)-diphenyldiazene-4,4′-bis(3-guaiazulenylmethylium) bis(hexafluorophosphate) are documented.