Question

In each reaction box, place the best reagent and conditions from the list below. There is more than one possible route. Note: If one or more reagents are incorrectly placed, a single red X will appear on the top left. CH3CHO, 2H2O CH2CH2CH2CHO, 2H2O CH3(CH2)2MgBr, H2O CH3MgBr, H2O CH3(CH2)2OH Mg CH3Br PCC HOCH2CH2OH, H+ H3O+

Answer 1

Concepts and reason

The concept used to solve this question is retrosynthetic analysis of the given product. In the retrosynthetic route, the last step of the synthesis is first determined and remaining steps can be fixed by functioning backwards from the product. Later, the given reagents can be placed in the order of conversion from starting material into product.

Fundamentals

Retrosynthetic analysis: In this analysis, the last step of the synthesis is first determined and remaining steps can be fixed by functioning backwards from the product. Simply telling, the synthesis of the target molecule in backward direction can be established in this strategy. This is also called as retrosynthesis (reverse synthesis). The retrosynthesis can be denoted by “ $\Rightarrow$ ” arrow.

Disconnection: It is an operation which breaks a bond in such a way that the target molecule converts into possible starting materials. Or it can be simply telling, it is reverse of chemical reaction.

FGI: In the retrosynthesis, functional group interconversion (FGI) takes place which means the conversion of one functional group into another functional group.

There are many numbers of routes to synthesize a target molecule but the most efficient way is taken into consideration.

The given staring material and the product (target molecule) is drawn as follows:

The retrosynthesis of the target molecule is as follows:

The target molecule could be synthesized by the deprotection of acetal group of the tertiary alcohol. The tertiary alcohol could be synthesized by the treatment of ketone with methylmagnesium bromide.

The ketone could be synthesized by the oxidation of secondary alcohol which in turn could be synthesized by the treatment of aldehyde with arylmagnesium bromide.

The arylmagnesium bromide could be synthesized by the treatment of aromatic bromo compound with magnesium metal which in turn could be synthesized by the protection of 4-bromobenzaldehyde with ethylene glycol in the presence of acid.

From the retrosynthesis of target molecule in step 1, it is clear that the synthesis consists of 6 steps.

The reverse order of retrosynthesis represents the actual chemical synthesis.

Therefore, the synthesis of the target molecule can be written as follows:

And, hence the sequence of reagents required for the synthesis of target molecule from the starting material from the given list can be written as follows:

$\begin{array}{l}\\1){\rm{ OHC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH, }}{{\rm{H}}^{\rm{ + }}}\\\\{\rm{2) Mg}}\\\\{\rm{3) 1}}{\rm{. C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{CHO, 2}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\\\{\rm{4) PCC}}\\\\{\rm{5) 1}}{\rm{. C}}{{\rm{H}}_{\rm{3}}}{\rm{MgBr, 2}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\\\{\rm{6) }}{{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\\\end{array}$

Ans:

The sequence of reagents required for the synthesis of target molecule from the starting material is as follows:

$\begin{array}{l}\\1){\rm{ OHC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH, }}{{\rm{H}}^{\rm{ + }}}\\\\{\rm{2) Mg}}\\\\{\rm{3) 1}}{\rm{. C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{CHO, 2}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\\end{array}$

$\begin{array}{l}\\{\rm{4) PCC}}\\\\{\rm{5) 1}}{\rm{. C}}{{\rm{H}}_{\rm{3}}}{\rm{MgBr, 2}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\\\{\rm{6) }}{{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\\\end{array}$