Rn. Warrener et al., REACTION OF DIENOPHILES WITH A 5,6-BISMETHYLENENORBORN-2-EN-7-ONE - THE SYNTHESIS OF A STABLE NORBORNA-2,5-DIEN-7-ONE, Australian Journal of Chemistry, 46(7), 1993, pp. 1009-1019
Reaction of hemicyclone (10) with (E)-1,4-dibromobut-2-ene (9) under f
orcing conditions yielded a 1 : 1 adduct (11) which served as the prec
ursor for the 5,6-bismethylenenorborn-2-en-7-one (12) through fluoride
-promoted dehydrobromination. The conjugated diene group in (12) enter
s into Diels-Alder reactions with reactive dienophiles to produce inte
rmediate norbornadienones en route to aromatic products. It has been p
ossible to identify the norborna-2,5-dien-7-one (16) resulting from th
e reaction of (12) with N-tolyltriazoline dione (15), thereby offering
authentic evidence for the rare norborna-2,5-dien-7-one ring system.
In addition, (12) has been used as a reagent to evaluate facial select
ivity in its reaction with the transient Dewar benzene (24). The cyclo
butamaleimide moiety in (24) is screened on each face, yet facial disc
rimination in its reaction with (12) is high (7:1). Thermolysis of the
5,6-bismethylenenorborn-2-en-7-one (12) yields the substituted benzoc
yclobutene (14), a reaction which may involve the o-xylylene (13) as i
ntermediate.