Azulenes, synthesis

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

The condensation of a vinylogous formamide with an enamine has been applied to an aza azulene synthesis (351). The point of attachment of the aldehyde to the enamine in condensations with indolenin derived poly-enamines was found to favor the second double bond (352,353). 

During the 1950s and 1960s Hafner used Konig salts, derived from the reaction of A -methyl aniline with Zincke salt 1, for azulene synthesis. The Zincke reaction also achieved prominence in cyanine dye synthesis and as an analytical method for nicotinamide determination. ... 

Reaction of benzene with diazoacetic esters to give cyclohepta-2,4,6-trienecarboxylic acid esters. Cf. Pfau-Platter azulene synthesis. 

An azulene synthesis involves the addition of 6-(iV,iV-dimethylamino)fulvene (208) to a thiophene sulfone (77TL639, 77JA4199). 

Early reports by Kossanyi and coworkers illustrate the variety of strained products that can be obtained from intramolecular photoreactions. For example, irradiation of 2-allylcyclohexanone gave a mixture of (186 32%), (188 22%) and (189 14%), the latter two arising presumably from decomposition of the strained tricyclic oxetane (187). In a related azulene synthesis,Kossanyi obtained high yields of oxetanes (190) and (191), the latter comprising 80% of the reaction mixture. When thermolyzed, compound (191) formed a mixture of isomeric dihydroazulene compounds that could be dehydrogenated (Pd/AhOs) to form azulenes. 

Azulene synthesis.10 The reaction between 6-(2-dimethylaminovinyl)fulvene (l)11 and dimethyl acetylenedicarboxylate (2) affords dimethyl 4,5-azulenedicarboxylate (3, 11 %) and dimethyl dimethylaminomaleate (4, ca 20%). 

The 4-methyl group of the azulenes (752) condense slowly as mentioned with (7) to give the red azulene-4-dieneamines (755). The latter are related to the dieneamino-fulvene (7) of the classical Hafner-azulene synthesis, and on heating afford in a (jrlOj)-ring-closure the cyclopenta(e,f)heptalenes (154)18> 72 rather than the benz(e)azulenes in a ( 6s)-cyclization. 

Pfau-Plattner azulene synthesis. Formation of azulenes by ring enlargement of indanes on addition of diazoacetic ester, hydrolysis, dehydrogenation, and decarboxylation of the resulting acid. 

Rigby synthesized a [5.3.1] oxa-bridged nucleus in the context of a perhydro-azulene synthesis [89]. Upon treatment of 81 with BF3 etherate, a hetero-Diels-Alder reaction between the aldehyde and the diene occurred to give 82 in good yield, Eq. 62. 

Ring fission of pyridinium ions with acceptor substituents, e.g. 7V-2,4-dinitrophenylpyridinium salts 221 (see p 280) leads, on treatment with secondary amines, to pentamethine cyanines 222 (Konig s salts). They condense with sodium cyclopentadienide to yield vinylogous aminofulvenes 223, which on cyclization produce azulene (azulene synthesis according to Ziegler and Hafner, see p 229 [73]) ... 

Furans. Aminoazulene 163b (Scheme 39) can be obtained from jS-dolabrin (163a) by Nozoe s azulene synthesis. Deamination is accompanied by furan-ring closure to yield azuleno[6,5- ]furan 164 and, after defunctionalization, compound 165 (61C1L1715). 

Pyridazines. Hafner et al. (78H(11)387) used variants of their azulene synthesis to construct azuleno[8,l-cd]pyridazines by... 

This reaction is similar to the Pfau-Plattner Azulene Synthesis. 

More experimental procedures are available in the literature. Other references related to the Pfau-Plattner azulene synthesis are cited in the literature. ... 

COjMe and R = COjMe, R = H). Related products were obtained using propiolaldehyde and l-diethylaminoprop-l-yne. According to frontier orbital theory, electron-rich dienes should add across the 1,6-positions of fulvenes. This prediction has been proved correct and the reaction developed into a new azulene synthesis, e.g. 6,6-dimethylfulvene and 1-diethylaminobutadiene react to give (107 65% isolated). ... 

Petrenko-Kritschenko Piperidone Synthesis Pfau-Plattner Azulene Synthesis Pfitzinger Reaction PFitzner-Moffatt Oxidation... 

Scheme 5 Aryl-substituted azulene synthesis via palladium-catalyzed C-H activation.

---