Ethynylazulenes — Building Blocks for Novel Oligoazulenes with Ethynyl and Butadiynyl Bridges

Abstract

The azulenes 3a,b, 6a,b, 9, 12 and 15 ethynylated in the fivemembered ring were prepared by Pd-catalysed cross-coupling of the corresponding iodoazulenes 1a,b, 4a,b, 7, 10 and 13, respectively, with trimethylsilylacetylene and subsequent desilylation. The synthesis of some acyclic oligomers 23-30, 32-36 and 38-40 from these ethynylazulenes could be accomplished by oxidative Eglinton coupling as well as Pd/Cu-

Molecular Transformation of 2‐Methylazulenes: An Efficient and Practical Synthesis of 2‐Formyl‐ and 2‐Ethynylazulenes

“…1 H NMR (500 MHz, CDCl 3 ): δ = 8.27 (d, J = 9.8 Hz, 2 H, 4,8‐H), 7.57 (t, J = 9.8 Hz, 1 H, 6‐H), 7.45 (s, 2 H, 1,3‐H), 7.19 (t, J = 9.8 Hz, 2 H, 5,7‐H), 3.48 (s, 1 H, C≡CH) ppm. The data are in agreement with those previously reported in ref …”

Cyclooligomerization of Mono‐ and Diazulenylethynes Catalyzed by Transition Metal Complexes

“…As already reported, [20,21] the syntheses of 1-ethynylazulenes 1a,b as well as 2-ethynylazulenes 2, besides di-and triethynylazulenes, were accomplished by utilizing the Pdcatalyzed cross-coupling reaction of the appropriate iodoazulenes with trimethylsilylacetylene (TMSA) under Sonogashira-Hagihara [26][27][28] conditions to furnish the protected ethynylazulenes followed by deprotection upon treatment with potassium hydroxide.…”

“…Moreover, we recently communicated the synthesis of the deep green bis(azulen-1-yl)ethynes 10a,b [21,23] by Sonogashira-Hagihara [26][27][28] coupling of the deprotected 1-ethynylazulenes 1a,b with 1-iodoazulenes.…”

“…Especially the azulene system should be suitable in this respect due to its remarkable polarizability and tendency to form stabilized cations and anions as well as radical cations and anions. [18,19] We recently developed simple routes to a series of mono-and polyethynylated azulenes, [20,21] and studied their transformations into linear oligoazulenes with ethynyl and butadiynyl bridges by Pd/Cucatalyzed as well as oxidative coupling reactions. [21,22] Furthermore, we previously reported on the first cyclooligomerization of mono-and diazulen-1-ylethynes by transition metal complexes as an efficient route to novel azulenyl-substituted benzenes and cyclobutadiene complexes.…”

“…[18,19] We recently developed simple routes to a series of mono-and polyethynylated azulenes, [20,21] and studied their transformations into linear oligoazulenes with ethynyl and butadiynyl bridges by Pd/Cucatalyzed as well as oxidative coupling reactions. [21,22] Furthermore, we previously reported on the first cyclooligomerization of mono-and diazulen-1-ylethynes by transition metal complexes as an efficient route to novel azulenyl-substituted benzenes and cyclobutadiene complexes. [23] According to the same methodology also some cyclooligomerizations of 2-and 6-ethynylazulenes were investigated later by Ito et al [24,25] Herein, we give a full account of the results of our studies.…”