 The other major reagent is a camphor @-@ derived reagent developed by <unk> Aggarwal of the University of Bristol . Both <unk> are easily synthesized , although the yields are lower than for the <unk> reagent . The ylide conformation is determined by interaction with the bridgehead <unk> and approach of the aldehyde is blocked by the camphor <unk> . The reaction employs a <unk> base to promote formation of the ylide . 
