Stereochemistry of 2,2,5 trisubstituted tetrahydrofuran ring containint natural products based on 1H NMR spectroscopy: Some observations

A hydrogen in 2,2,5 trisubstituted tetrahydrofuran ring of some natural products appears as a triplet when the largest groups were cis oriented and as a doublet of doublet when they were trans oriented. In compounds containing one THF ring, esterification/etherification of a hydroxyl group in the side chain carbon attached to position 2 of the THF ring was found to convert a triplet (in compounds not derivatized) into an atypical dd in the case of cis configured compounds and a typical dd into an atypical dd or a triplet in the case of trans configured compounds. Esterification/etherification of the hydroxyl elsewhere in the molecules did not affect the splitting pattern.