What should be the correct sequence of reagents to be used in this reaction?


> 
> The correct sequence of reagents for the following conversion will be
> 
> 
> [![Reaction image](https://i.stack.imgur.com/obhcK.jpg)](https://i.stack.imgur.com/obhcK.jpg)
> 
> 
> (1) $\ce{CH3MgBr, H+/CH3OH, [Ag(NH3)2]+OH-}$
> 
> 
> (2) $\ce{CH3MgBr, [Ag(NH3)2]+OH-, H+/CH3OH}$
> 
> 
> (3) $\ce{[Ag(NH3)2]+OH-, CH3MgBr, H+/CH3OH}$
> 
> 
> (4) $\ce{[Ag(NH3)2]+OH-, H+/CH3OH, CH3MgBr}$
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> 
> 


I think the correct option is (3), however, the key says it is (4).


The first step is definitely the oxidation of the $\ce{-CHO}$ group to $\ce{-COOH}$ using Tollen's reagent. But I think that the second step should be to use Grignard reagent to form tertiary alcohol and then acidify it. Because if we first acidify and then use Grignard reagent, the $\ce{CH3MgBr}$ will react with the leftover acid and the $\ce{CH3OH}$ due to its mildly acidic proton.


Also, I am rather doubtful that the $\ce{CH3MgBr}$ will even react with the acid formed in the first step since it will be in the form of $\ce{R-COO^-Ag+}$, which is not electrophilic.


So what is the correct answer? And how would the $\ce{CH3MgBr}$ react with the acid?
Thank you.


