As I mentioned previously, I think Weinreb amides (the RNMeOMe species) react with organolithiums to form ketones.
So, after forming the alcohol (or more probably the alkoxide in this case, as I don't see any acid in your conditions), I think the tetrahedral intermediate collapses and kicks out -NMeOMe.
Initial product perhaps the keto-acetylene? I'm not sure how labile TMS is in your system, this may fall off?
S