[stewie griffin]

Quick question.. when you run a hydroboration reaction with 9-BBN, do you see the intermediate borane on TLC? In other words, can one track the reaction by TLC according to appearance of the hydroborated material (but not yet oxidized) or do you simply have to go by disappearance of starting material.

[OC pro]

Since you form a stable intermediate its should be visible (and in case of non UV-active compounds stainable with iodine or cer/molybdate dip). The product will be much more polar. You can follow the disappearance of starting material of course.
But you could also quench a small aliquote with NaOH/H2O2 in a small vial, then water and ethyl acetate and make a TLC of the ethyl acetate layer (to detect the product alcohol).
The quenching method (mimicking a work-up of the reaction "in vial") is used in my company in almost any cases when performing TLC.

[lavoisier]

The product will be much more polar.

Are you sure a 9-BBN adduct will be more polar? The BBN moiety is one big lump of fat... but I might be wrong.
Other observation, I don't know what the stability of the BBN adduct is, but I remember you can reduce double bonds by treating a borane adduct with an organic acid (e.g. AcOH). So if silica is acidic enough to do the same, you might in fact see the redcuced compound.

[discodermolide]

you won't see the intermediate borane on TLC, follow by disappearance of starting material.

[MissPhosgene]

you can always try it out to see if its visible