$\begin{array}{*{20}{c}}
{OH\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{C{H_3}CHC{H_2}C{H_2}N{H_2}}
\end{array}$ $\xrightarrow[{triethyla\min e}]{{ethyl\,formate\,\left( {1\,equiv} \right)}}$
$C{H_3}C{H_2}OH\xrightarrow{{P + {I_2}}}A\xrightarrow[{ether}]{{Mg}}B\xrightarrow{{HCHO}}C\xrightarrow{{{H_2}O}}D$