Homochiral α-substituted γ-lactols3and4derived from (R)-pantolactone1were used in 2-lithio-1,3-dithiane additions to afford very high controls in diastereoselectivities arising from 1,2-asymmetric inductions. Thus non-chelation controlled nucleophilic addition on3gave theantidiastereomer5as the major product (92% de), while the chelation controlled addition on4furnished thesyndiastereomer7(96% de) as the almost exclusive product. The stereochemical outcomes of these reactions were proven unambiguously by locking the conformation of thesyn- andanti-triol adducts7and8through their respective acetonides and by nuclear Overhauser enhancement measurements. The lack of 1,3-dioxolane formation in the case of theanti-triol8was taken as a further confirmation of the absolute configuration at the newly created stereocenter.Keywords: byrostatin, pantolactone, α-hydroxylactol, dithiane.