\( \to C{H_3}CHO\xrightarrow{{[O]}}\mathop {C{H_3}COOH}\limits_{{\text{acetic}}\,\,\,{\text{acid}}} \)
$C{H_3}COOH + PC{l_5} \to A\mathop {\xrightarrow{{{C_6}{H_6}}}}\limits_{anh.\,AlC{l_3}} $ $B\mathop {\xrightarrow{{{C_2}{H_5}MgBr}}}\limits_{ether} C$