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Face Selectivity of the Diels-Alder Reaction of 5,6-Bis((D)methylidene)-2-bicyclo[2.2.2]octene

✍ Scribed by Macro Avenati; Pierre Vogel

Publisher
John Wiley and Sons
Year
1983
Tongue
German
Weight
598 KB
Volume
66
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The face selectivity (endo‐face vs. exo‐face attack onto the exocyclic s‐cis‐butadiene moiety) of the [4+2]cycloadditions of 5,6‐bis((D)methylidene)‐2‐bicyclo‐[2.2.2]octene (11) to strong dienophiles has been determined in benzene at 25°. It is ca. 95/5, 75/5, 70/30, 60/40 and 50/50 for N‐phenyltriazolinedione (NPTAD), tetracyanoethylene (TCE), dimethyl acetylenedicarboxylate (DMAD), maleic anhydride (MA) and singlet oxygen (^1^O~2~), respectively. The endo‐face preference is probably due to a participation of the homoconjugated double bond at C(2), C(3) which makes the etheno bridge more polarizable than the ethano bridge in 11. The absence of face selectivity with ^1^O~2~ is consistent with an entropy‐controlled mechanism involving the intermediacy of an exciplex.

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