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Synthesis and Diels-Alder Reactivity of 2,3,5,6-Tetramethylidenenorbornane

✍ Scribed by Olivier Pilet; Pierre Vogel

Publisher
John Wiley and Sons
Year
1981
Tongue
German
Weight
519 KB
Volume
64
Category
Article
ISSN
0018-019X

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✦ Synopsis

Pd-catalyzed double carbomethoxylation of the Diels-A lder adduct of cyclopentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5,6-exotetracarboxylate (4) which was transformed in three steps into 2,3,5,6-tetramethyIidenenorbornane (1). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25") than the addition of TCNE to 7 yielding the bis-adduct 9. Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane (2). The following second order rate constants (toluene, 25 ") and activation parameters were obtained for: l+TCNE+7:k,=(:!55 ! 5 ) lop4 rno1-l . s-l, dH,=(12.2+0.5) kcal/mol, dS+=(-24.8+1.6) eu.; 7+TCNE+9, k2=(0.7k0.02) mol-'. s-l, dH+=(14.1+ 1.0) kcal/mol, dSP=(-30k3.5) eu.; 2+TCNE+8: kl=(1.5&0.03) mol-' . s-', dH+=(14.8&0.7) kcal/mol, dSf=(-26.4+2.3) eu.; 8+TCNE-10: k2=(0.004+0.0002) mol-' . s-l, AH* = (17 -t 1.5) kcal/mol, AS* = (-3 0 k 4) eu. The possible origins of the relatively large rate ratios kllk2 are discussed briefly.

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Synthesis and Diels-Alder Reactivity of
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## Abstract A short synthesis of the title compound **13** is reported. The acetal group in **13** enables one to control the regio‐ and stereoselectivity of the two successive __Diels__‐__Alder__ additions of the tetraene. The first addition is significantly faster than the second one, thus making