[Rutherford]

Not the reduction, but the hydrolysis with H₂O (below LiAlH₄).

[Dan]

You need an acid catalyst to hydrolyse a ketal, water alone won't do it.

[Rutherford]

Oh, wait I wrote step S T which is the one with HCl, so HCl should decompose it.

[Dan]

Please post clearly what you think each structure is and label them with the letters as in the schemes so as to make them unambiguous.

[Rutherford]

I intended to do that at the end. Here it is.

[discodermolide]

An interesting way of α-bromination of acetone with concomitant ketallisation. (see page 1 of thread)

[Rutherford]

I got a problem with N and O isomers (the ketals in the first scheme). The tip was: N and O are isomers; ωH = 3.8%; ωC = 22.9%.
The formula of the ketal is C₅H₁₀O₂Br₂ (the left compound in the picture). Its molar mass is 262 g/mol while the molar mass according to the elemental analysis should be 263 g/mol. There is a difference here  .

[Dan]

It's just a rounding error. For 262 g/mol you get...

For the 10H: (10 x 1)/262 = 0.038 (3.8%)
For the 12C: (5 x 12)/262 = 0.229 (22.9%)

[Rutherford]

Okay, I suppose that the scheme I posted is right.