... Tetrahedron Letters. Volume 55, Issue 16, 16 April 2014, Pages 2687–2690. ... 4), the five-membered rings are slightly distorted from planarity (torsion angles O1–I1–C1–C2 = 9.27(15)°, O2–I1–C1–C6 = 8.10(16)°); when one of the ether rings is replaced by the lactone ring, just as ...