Methyl (+/-)-(1 alpha,1a alpha,3a alpha,6a alpha,6b ethyl-3,6-,dioxa-c
yclobut[cd]indene-1-carboxylate, C15H22O5, adopts a hemispherical conf
ormation with the methoxy, methoxycarbonyl and vinyl groups pointing o
utwards from the hemisphere, The tetrahydropyran ring is in a chair co
nformation and the tetrahydrofuran ring is in an envelope conformation
.