1.4- Dimethyl-azulene

Nach dem gleichen Schema gelang W. Herz (60) die Gewinnung von trialkylierten bicyclischen Azulenen, von 2,4,5-Trimethyl-[56] und von 2-Isopropyl-4,5-dimethyl-azulen [60]. 

Das analog dargestellte l,4,8-Trimethyl-[41] und 1,4-Dimethyl-8-isopropyl-azulen (58), [42] sind violettstichig blau. Beim Versuch der Synthese des 1 -Isopropyl-4,8-dimethyl-azulens iiber das 1-Isopropyl-4,7-Dimethylhydrinden trat Wanderung der Isopropylgruppe von 1 nach 2 zum 2-Isoprapyl-4,8-dimethyl-azulen (59), [61] (Vetivazulen) ein. 

Kurz darauf beschrieben H. Arnold und K. PaHls (8) die Reduktion von 4,8-Dimethyl-azulen-6-carbonsaure-athylester bei —60° mit dem gleichen Reduktionsmittel zu dem entsprechenden primaren Alkohol [66], der fiber das Azulenpyridinium-tosylat und Nitron in den 4,8-Dimethyl azulenaldehyd- (6) [77] iibergefiihrt wurde. Dieser erste synthetische Azulenaldehyd ist im Zusammenhang mit dem Lactaroviolin, einem von H. Willstaedt (184) aus dem echten Reizker isolierten Aldehyd von Interesse. 

An attempted synthesis of 1-isopropyl-4,8-dimethyl-azulene. Migration of... 

Dimethylaziridiiie, mesa- and dl-, 741 Dimethyl azodicarboxylate, 850 Dimethyl azulene-l,2-dicarboxylate, 272... 

When heated to high temperatures the 9,10-dimethyl derivative is converted into 1,2- and 2,3-dimethylnaphthalenes and 1,2-dimethyl-azulene [220]. 

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. 

Durch Kondensation von Furfurol mit Propionaldehyd statt Acetaldehyd und uber die gleichen Abwandlungen wie im vorstehenden Schema erhielt Pommer 5-Methyl-azulen [67], 5,8-Dimethyl- [65] und 5-Methyl-8-Isopropyl-azulen [72], wahrend 5-Methylfurfurol und Propionaldehyd zum 1,5-Dimethyl- [21] und zum 1,5,8-Trimethylazulen [43] fiihrten. 

F. Sorm und L. Urbanek (123) dehydrierten den zuerst von Y. Asa-hina und T. Tsukamoto (9) aus dem atherischen Ol von Daucus carota gewonnenen Sesquiterpenalkohol Carotol, der wohl mit dem Daucol von Richter (115) aus dem gleichen Ol identisch ist, mittels Palladiumkohle zu einem Azulen, das kein Trinitrobenzolat bildete. Daneben entstand 1, 7-Dimethyl-4-isopropyl-naphthalin. 

Wittig reactions with pyrrole-2-aldehyde led to the esters (79) which were cyclisized to 3a-azaazulen-4-ones (80).104,105 4-Methylene-3a-aza-azulenes (81) have been obtained from 80 with stabilized phos-phoranes.36 Reaction of dimethyl acetylenedicarboxylate with 81 could not be achieved. A similar cycloaddition was successful in the synthesis of cycl[3,3,3]azines (2) (Section V). 

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