Abstract
Reaction of 1-ethoxycarbonyl-2-oxocycloheptaneacetic acid with naphthalene-2-sulphonic acid in boiling xylene gives 8-oxabicyclo[5,3,0]dec-1(10)-en-9-one and, mainly, ethyl 9-oxo-8-oxabicyclo[5,3,0]dec-6-ene-1-carboxylate. Reduction of the latter with lithium hydridotri-t-butoxyaluminate in tetrahydrofuran affords a mixture of ethyl
endo
- and ethyl
exo
-hydroxy-9-oxobicyclo[4,2,1]nonane-1-carboxylates, in which the
endo
-compound predominates. These products are thought to be formed by way of 1-ethoxycarbonyl-2-oxocycloheptaneacetaldehyde.
Dehydration of the two ketols by treatment of the toluene-
p
-sulphonates with boiling collidine leads to a mixture of ethyl 9-oxobicyclo[4,2,1]non-7-ene-1-carboxylate and the strained bridgehead olefin, ethyl 9-oxobicyclo-[4,2,1]non-6-ene-1-carboxylate. The structural assignment of the latter compound is based on its spectroscopic properties and on its rapid hydrogenation to ethyl 9-oxobicyclo[4,2,1]nonane-1-carboxylate. The Δ
7,8
-isomer was converted by standard reactions into 1-methylbicyclo[4,2,1]nonan-9-one and 1-methylbicyclo[4,2,1]non-7-en-9-one. Reaction of the latter with dimethylsulphoxonium methylide gave the oxiran, but the corresponding 9-
anti
-hydroxy-compound could not be converted into the bromide.