TMS-propyne

In looking over the sequence, I wonder if there is still room for improvement. Surely some effort on the alkylation of lithiated TMS-propyne might raise the efficiency of this lowest yielding step. Quite likely the Ni(0)-catalyzed coupling, which stands conservatively at 88%, can be increased perhaps substantially, as virtually all of the model systems on which it is based proceed in yields > 90%. But this is not for us to do rather, should our academic route be pursued by industrial... 

When allene (200) is treated with two equivalents of butyllithium and of Me3SiCl 196 (R = H) is formed (equation 94)119a. If TMS-acetylene (57a) reacts with ethylmagnesium bromide in the presence of N,iV-dimethyl formamide, 3-TMS-propynal (201) can be isolated (69% yield) which can form 2-TMS-ethynyl-l,3-dioxane (202) with 1,3-propa-nediol in 81% yield (equation 95)120. 

Isomeric Species. The isomeric substituted lithium acetyhde LiC=C-CH2TIPS (4), from 3-TIPS-propyne, was silylated to l-TMS-3-TIPS-propyne. Compound (4) isomerizes to (1) in THF/HMPA solution at rt, as shown by isolation of pure 1-TIPS-propyne after quenching a solution of (4) with H2O7... 

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