The stereochemistry of isocolumbin: X-ray analysis of the 1-p-iodophenyl-3-phenylpyrazoline adduct of isocolumbin

Abstract

A suitable heavy atom derivative of isocolumbin has now been found in the 1-p-iodophenyl-3-phenylpyrazoline adduct (III) which crystallises as a monoacetone solvate in the tetragonal space group P4₁2₁2 with eight molecules of C₃₃H₃₁O₆N₂I,(CH₃)₂CO in a unit cell of dimensions a=b= 9·68, c= 70·79 Å. With initial phasing on the iodine atom, the crystal structure was solved by three-dimensional Fourier and least squares calculations. The final value of R over 1860 independent reflections was 9·5%. The results establish structure (III) for this derivative and hence confirm structure (II) for isocolumbin. The molecular dimensions and the stereochemistry of the three boat shaped six-membered rings and the 0-lactone systems are discussed.