Copper compounds sulfinate

Stereoselective conversion of propargylic compounds to haloallenes normally proceeds with high anti stereoselectivity. On the other hand, syn selectivity is observed for the copper(I) bromide hydrobromide induced conversion of propargylic alcohol into the corresponding 1-bromoallene with low enantiomeric excess (6% ee). The sulfinate ester, however, again gave anti stereoselectivity with moderate enantiomeric excess150. 

In attempts to recover the chiral Ugand 21, the analogous oxidized phosphoric amide was also isolated. This compound is formed by a copper-catalyzed side-reaction with sulfinate as oxidant and actually works as a cocatalyst that significantly increases the enantioselectivity of the AIMe3 additirai. A similar effect was achieved applying a combination of 21 and hexamethylphosphoric triamide (HMPA), and thus, the improved stereoselectivity was suggested to arise from strong coordination effects. 

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