Asymmetric synthesis, stereochemistry and rearrangement reactions of naturally occurring 7′-hydroxylignano-9,9′-lactones

The asymmetric synthesis of a series of (7′S,8R,8′R)-7′-hydroxylignano-9,9′-lactones is presented, among them the mammalian lignan (7′S)-hydroxyenterolactone and (7′S)-parabenzlactone, allowing the stereochemistry of natural occurring (–)-parabenzlactone to be re-assigned. A hydroxylactone rearrangement and its possible mechanisms are discussed. Finally a brief survey of the current naming and numbering variants of 7′-hydroxylignano-9,9′-lactones is presented, along with a suggestion for harmonization of the nomenclature.