A Synthesis of 3-Alkyl-l-Naphthols

Standard Heck coupling of o-bromopropiophenone with propyne proceeds in 72% yield. Deprotonation of the product thus formed with KHMDS in toluene at -78°C followed by heating at 75°C for one hour gave 3-methyl-1-naphthol in 74% yield after acidic work-up and distillation. This approach has proved to be general and efficient for the preparation of a variety of 3-alkyl-1 -naphthols. 

Suggest a mechanism for formation of the 3-methyl-l-naphthol which is consistent with the observation that similar cyclisation of the deuterated alkyne 1 gave the naphthol 2. What conclusion can be drawn from the fact that use of t-butylacetylene instead of propyne in the above sequence gives 3-t-buty 1-1 -naphthol in 75% yield for the cyclisation step  

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