$C{H_2} = C{H_2}\, \xrightarrow{{HOCl}} \,A\xrightarrow{{_R}}\begin{array}{*{20}{c}}
{C{H_2}OH} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{C{H_2}OH}
\end{array}$
$C{H_3}C{H_2}OH\xrightarrow{{P + {I_2}}}A\xrightarrow{{Mg}}B\xrightarrow{{HCHO}}C\xrightarrow{{{H_2}O}}D$