The cyclic compound $\mathrm{S}$ is:

Identify ($\mathrm{S}$) in the following sequence of reaction:

The product formed in the reaction is

Identify the structure of '$\mathrm{G}$'.

Identify the structure of [B].

The reagent $\mathrm{R}$ may be

$$\begin{gathered} \mathrm{I}. {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{MgBr} \mathrm{II}. {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Li} \\ \mathrm{III}. {\left({\mathrm{CH}}_3{\mathrm{CH}}_2\right)}_2\mathrm{Cd} \mathrm{IV}. {\left({\mathrm{CH}}_3{\mathrm{CH}}_2\right)}_2\mathrm{CuLi} \end{gathered}$$

In the above chemical reaction, $\mathrm{B}$ may be:

The reaction mainly produces:

${\mathrm{BrCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br} +\mathrm{Mg} \stackrel{{\mathrm{Et}}_2\mathrm{O}}{\to }$