Investigations into the construction of the penta­substituted ring C of Neosurugatoxin – a crystallographic study

The crystal structures of three cyclo­penta­[c]furans with various substituents at the 4-, 5- and 6-positions of the ring system are reported, namely, (±)-(3aR,4S,5S,6aS)-4-methyl-5-phenyl­hexa­hydro-1H-cyclo­penta­[c]furan-4,5-diol, C(14)H(18)O(3), (I), (±)-(3aR,4S,5S,6aS)-4-benz­yloxy-4-methyl-5-phenyl­hexa­hydro-1H-cyclo­penta­[c]furan-5-ol, C(21)H(24)O(3), (II), and (±)-(1aR,1bS,4aR,5S,5aR)-5-benz­yloxy-5-methyl-5a-phenyl­hexa­hydro-2H-oxireno[2′,3′:3,4]cyclopenta­[1,2-c]furan, C(21)H(22)O(3), (III). The dominant inter­action in (I) and (II) is an O—H⋯O hydrogen bond across the bicyclic 5,5-ring system between the non-functionalized hy­droxy group and the tetra­hydro­furan O atom, which appears to influence the envelope conformations of the fused five-membered rings, whereas in (III), the rings have different conformations. A weak intra­molecular C—H⋯O inter­action appears to influence the degree of tilt of the phenyl ring attached to the 5-position and is different in (I) compared to (II) and (III).