New Synthesis of 2H‐Benzazulenes

Abstract

Acenaphthylene ( I ) combines with ethoxycarbonylcarbene, generated by thermolysis of ethyl diazoacetate, t o give the stable cyclopropane derivative (21, which can be converted into phenalenium perchlorate (3) via a multi-step synthesis "1. H, /cOOC, H,

The Effect of Benzannulation on the Structures, Reactivity and Molecular Dynamics of Indenes, Pentalenes, Azulenes and Related Molecules

“…Early syntheses of a number of benzazulene isomers led to air-sensitive and thermally unstable materials in only modest yields. Typically, as shown in Scheme 26, Hafner and Rieper reported that treatment of cyclopent[cd]azulene with ethyl diazoacetate, i.e., a carbene addition process, led ultimately to ring expansion of a five-membered ring and, upon tautomerisation of the initially formed product, furnished ethyl 7,9-dimethyl-2Hbenz[cd]azulene-4-carboxylate, 72 [43]. Early syntheses of a number of benzazulene isomers led to air-sensitive and thermally unstable materials in only modest yields.…”

“…Early syntheses of a number of benzazulene isomers led to air-sensitive and thermally unstable materials in only modest yields. Typically, as shown in Scheme 26, Hafner and Rieper reported that treatment of cyclopent[cd]azulene with ethyl diazoacetate, i.e., a carbene addition process, led ultimately to ring expansion of a five-membered ring and, upon tautomerisation of the initially formed product, furnished ethyl 7,9-dimethyl-2Hbenz[cd]azulene-4-carboxylate, 72 [43]. As shown in Schemes 27-29, some years later, Jutz and Schweiger [44] found that, under basic conditions, 6-methylazulene and trimethinium perchlorate condense to generate the azulene-dienamine, 73, that isomerised upon heating to form 74, now poised for an electrocyclic ring closure and loss of dimethylamine to form ultimately the benz[f]azulene, 75.…”

Selective ring expansion and C−H functionalization of azulenes

“…Dirhodium catalysts, pioneered by Noels 28 offered significant advances, and various substituted benzene derivatives could be used to obtain useful products with good yields and regioselectivity. Nevertheless, the Buchner reaction produced ring expansion of 6- to 7-membered rings in all cases, and the expansion of a non-benzenoid 5-membered ring to produce a 6-membered ring remained unknown to date 29 . Conversely, 3-halopyridines were prepared from the reaction of pyrrole with haloform-derived carbenes in 1881 30 .…”