Heptalene
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| Surname | Heptalene | ||||||||||||
| Molecular formula | C 12 H 10 | ||||||||||||
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| Molar mass | 154.21 g mol −1 | ||||||||||||
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||
Heptalen is a bicyclic unsaturated hydrocarbon consisting of two fused cycloheptatriene rings. Like pentalen , it is a homologous compound of naphthalene . According to Hückel's rule , this compound with 12 π electrons is not to be counted among the aromatics , rather it is an anti- aromatic system that behaves like a non- mesomeric stabilized polyene .
presentation
There are several routes for the preparation of heptals, in which a carbocyclic structure with 10 carbon atoms is formally converted into heptalene by the addition of a C 2 component. Naphthalene , 1,4,5,8-tetrahydronaphthalene or azulene can be used as the starting component.
Example of a multi-stage heptalenes synthesis according to Emanuel Vogel :
Multi-step synthesis of heptalen according to E. Vogel
Starting from naphthalene ( 1 ), 1,4,5,8-tetrahydronaphthalene ( 2 ) is obtained by means of a Birch reduction . In the next step, the bridgehead double bond is reversibly protected by converting it into an epoxy function . The oxirane derivative ( 3 ) formed in this way is converted into the pentacycle ( 4 ) by double carbene addition with a large excess of bromoform and 50% sodium hydroxide solution , which is then converted with lithium and tert-butanol in tetrahydrofuran to form the tetracyclic ( 5 ) is reduced. An allyl bromination is then carried out with N- bromo succinimide ( Wohl-Ziegler reaction ). Intermediate 6 is dehalogenated with zinc in THF , opening the two three-membered rings, to give 3,8-dihydroheptalene ( 7 ). The conversion of the compound 7 into the target compound 8 succeeds with a two-stage oxidation with triphenylmethyl hexafluoroantimonate and trimethylamine .
properties
The unsubstituted heptalene is an unstable compound. It can be converted relatively easily and reversibly into the corresponding heptalenium salt by treatment with acids. The heptalenium salts can therefore be used as heptalen preserves.
Heptalenium salts as heptalen preserve
The heptalenium salt with the cycloheptatrienylium structural element is an aromatic compound.
Individual evidence
- ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
- ↑ Hans Beyer: Textbook of organic chemistry . 18th edition. S. Hirzel Verlag, Stuttgart 1976, ISBN 3-7776-0342-2 , p. 575 f .
- ^ Gerhard Becker, Heinz Kolshorn: Heptalene . In: Heinz Kropf (Ed.): Houben-Weyl Methods of Organic Chemistry . Vol. V / 2c. Georg Thieme Verlag, Stuttgart, New York 1985, ISBN 3-9801412-1-7 , pp. 418 ff . ( limited preview in Google Book search).