You can add 2.5 eq n-buLi and stir the mixture for a while. And then, dump everything into water.
I'm skeptical that this will give the desired diol (though it could if ...). Please show the mechanism.
NVM, I was wrong. The cold whether decreases the momentum of my mind.
If you do as what I just said, the reaction goes the other way. And you will end up having hexane, not diol.
However, you use 1,4-dibromobutane and t-BuLi mixture to have the lithium halogen exchange, then react with excess amount of Formyl chloride, you should end up having dialdehyde. And you can reduce this to diol.
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The reaction above will be highly exothermic, even explosive.----------------------------------------------