The most successful reagents employed in a stoichiometric fashion are shown below . The first is a bicyclic oxathiane that has been employed in the synthesis of the β @-@ adrenergic compound dichloroisoproterenol ( DCI ) but is limited by the availability of only one enantiomer of the reagent . The synthesis of the axial diastereomer is rationalized via the 1 @,@ 3 @-@ anomeric effect which reduces the nucleophilicity of the equatorial lone pair . The conformation of the ylide is limited by transannular strain and approach of the aldehyde is limited to one face of the ylide by steric interactions with the methyl substituents .