Two isomeric cucurbitane derivatives.

Two isomeric cucurbitane derivatives, 3beta,7alpha,11beta-triacetoxycucurbit-5(10)-ene, (I), and 3beta,7alpha,11beta-triacetoxy-5alpha-cucurbit-1(10)-ene, (II), both C(36)H(58)O(6), have their single endocyclic C=C double bonds in different positions. This results in differences in the conformation of the four-ring system, which is close to a half-chair/half-chair/chair/half-chair arrangement in (I) and to a half-chair/twist-boat/boat/half-chair arrangement in (II). The orientation of some of the substituents is also different; the 3beta-acetoxy group is in an equatorial position in (I) but in an axial position in (II), while the 11beta-acetoxy group occupies an axial position in (I) and an equatorial position in (II). The asymmetric unit of (I) contains two symmetry-independent molecules which do not differ significantly, being related by a pseudo-twofold axis of symmetry. In both structures, the aliphatic chain fragments are disordered and the disorder persists at lower temperatures.