$CH \equiv CH$ $ \xrightarrow {CH_3MgBr}$ $ \xrightarrow {Co_2/H_3O^+}$ $ \xrightarrow {HgSO_4/H_2SO_4}$ $ \xrightarrow {Ag_2O,\Delta}$ $?$
$\underset{1}{\mathop{\begin{matrix}
O\,\,\,\,\,\,\,\,\,\,\,\, \\
||\,\,\,\,\,\,\,\,\,\,\,\,\, \\
C{{H}_{3}}COCHC{{H}_{3}} \\
\end{matrix}}}\,$ $\underset{2}{\mathop{\begin{matrix}
\,\,\,\,O \\
\,\,\,\,|| \\
C{{H}_{3}}CCl \\
\end{matrix}}}\,$ $\underset{3}{\mathop{\begin{matrix}
O\,\,\,\,\,\,\,\,\, \\
||\,\,\,\,\,\,\,\,\, \\
C{{H}_{3}}CNHC{{H}_{3}} \\
\end{matrix}}}\,$