$RCN{\mkern 1mu} \xrightarrow{{reduction}}{\mkern 1mu} (a),$
$RCN{\mkern 1mu} {\mkern 1mu} \mathop {\xrightarrow{{(i){\kern 1pt} C{H_3}MgBr}}}\limits_{(ii){\kern 1pt} {H_2}O} {\mkern 1mu} (b),$
$RNC{\mkern 1mu} {\mkern 1mu} \xrightarrow{{hydrolysis}}{\mkern 1mu} {\mkern 1mu} (c),{\mkern 1mu} $
$RN{H_2}{\mkern 1mu} \xrightarrow{{HN{O_2}}}{\mkern 1mu} {\mkern 1mu} (d)$
(1) (2) $CH_3CH_2NH_2$
(3) $(CH_3)_2NH$ (4) $\begin{array}{*{20}{c}}
O \\
{|\,|} \\
{C{H_3} - C - N{H_2}}
\end{array}$