Ready access to bridgehead olefinic isomers of the triquinacene skeleton
✍ Scribed by Holger Butenschön; Armin de Meijere
- Publisher
- Elsevier Science
- Year
- 1983
- Tongue
- French
- Weight
- 264 KB
- Volume
- 24
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
l-Halo-and 1,4-dihalotriquinacenes readily react with secondary amines and alkyl lithium compounds to yield bridgehead olefinic and double bridgehead olefinic derivatives of the tricyclo[5.2.1.04*10 ldecatriene system, probably by an $2' type attack of the soft nucleophile. The long searched-for acepentalene (1) possesses the same carbon skeleton as triquinacene (2), and therefore the latter has been suggested as a potential precursor to 1 [' I. With regard to its thermodynamic stability 1 probably not only suffers from an unfavorable Z-electronic system[21, but also from a considerable amount of bond and angle strain. Among the 16 isomeric tricyclo[5.2.1.04~10 ldecatrienes 2 is the only one without a bridgehead double bond. According to force field calculations[3] performed on the three isomeric monoolefins 3 -5[41 all other 15 isomers of 2 are predicted to be less stable than triquinacene (2). In fact, 3 was calculated to be 4.1 kcal/mol more stable than the bridgehead olefin 4, and 4 in turn 12.2 kcal/mol more stable than the twofold bridgehead olefin 5, in which all four substituents on the double bond must be bent out of plane.
3 4 5 AH#callmole) 6.83 10.96 23.16 Under these circumstances it is of particular interest that bridgehead olefinic tricyclo[5.2.1.04*101decatriene derivatives are readily accessible from the less strained triquinacene system. Reaction of bridgehead mono-and dihalo-triquinacenes 6 [5,61 with a number of secondary amines and with alkyl lithium reagents in general lead to the allylrearranged bridgehead olefinic derivatives 7 (see scheme 1 and table 1).