Pfau-Plattner azulene synthesis

Azulene formation from indanes and diazoacetates. Cf. Buchner ring expansion. 

The diazo compound is depicted as a carbene equivalent in the mechanism 

Quinoline-4-carboxylic acids from the condensation of isatic acids and a-methylene carbonyl compounds using base. 

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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. 

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. ... 

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

Of the fundamental nonalternant hydrocarbons, only two prototypes were known about fifteen years ago azulene (XI, Fig. 5), the molecular structure of which was determined by Pfau and Plattner and fulvene (XIX) synthesized by Thiec and Wiemann. Early in the 1960 s many other interesting prototypes have come to be synthesized. Doering succeeded in synthesizing heptafulvene (XX) fulvalene (XXI) and heptafulvalene (XXIII). Prinzbach and Rosswog reported the synthesis of sesquifulvalene (XXII). Preparation of a condensed bicyclic nonalternant hydrocarbon, heptalene (VII), was reported by Dauben and Bertelli . On the other hand, its 5-membered analogue, pentalene (I), has remained, up to the present, unvanquished to many attempts made by synthetic chemists. Very recently, de Mayo and his associates have succeeded in synthesizing its closest derivative, 1-methylpentalene. It is added in this connection that dimethyl derivatives of condensed tricyclic nonaltemant hydrocarbons composed of 5- and 7-membered rings (XIV and XV), known as Hafner s hydrocarbons, were synthesized by Hafner and Schneider already in 1958. 

The first chemical synthesis of azulene was reported by Pfau and Plattner in 1937. Their synthesis takes advantage of the ring enlargement of indane 133 on addition of diazoacetic ester to give cycloheptatriene 135. This compound is converted into azulene via a three-step sequence hydrolysis, dehydrogenation, and decarboxylation of the resulting acid. 

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