Reaction Mechanism for the Lithium Acetylide Addition to pMB Protected Amino Ketone

1 Reaction Mechanism for the Lithium Acetylide Addition to pMB Protected Amino Ketone 41 

Before starting to describe detailed studies on the mechanism, we would like to summarize what we know about the reaction so far  

1) Two equiv of cyclopropylacetylene and two equiv of norephedrine derivative 46 are required to obtain good conversion and high enantiomeric excess. 

2) Aging a mixture of lithium acetylide and the lithium alkoxide of 46 at higher temperature (-10 to 0°C) prior to addition of ketone 41 is needed to obtain constantly high enantiomeric excess. 

A few questions come to mind. What is the structure of the aggregate and why are 2 equiv of each reagent essential Is it due to the acidic proton (N-H) in 41 Before going into the detail of the mechanism, let us assemble more circumstantial evidence on this reaction. 

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