In this task, you will be given a passage to read. A fill in the blank question will be given to you. Your answer should fit the blank appropriately.
Q: 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 @-@ 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 . The other major reagent is a camphor @-@ derived reagent developed by Varinder Aggarwal of the University of Bristol . Both enantiomers are easily synthesized , although the yields are lower than for the oxathiane reagent . The ylide conformation is determined by interaction with the bridgehead hydrogens and approach of the aldehyde is blocked by the camphor moiety . The reaction employs a phosphazene base to promote formation of the ylide . fill in the blank : The most successful reagents employed in a stoichiometric __________________ are shown below .
A:
fashion