[cyanzi]

The question says  to devise a scheme to prepare threonine from 4-hydroxybutanoic acid (HOCH₂CH₂CH₂COOH)

So far, I've done this:
HOCH₂CH₂CH₂COOH ^Br₂/LDA  HOCH₂CH₂CHBrCOOH  ^{conc. H₂SO₄} H₂C=CHCHBrCOOH ^H+/H₂O CH₃CHOHCHBrCOOH ^NH_3(alc) CH₃CHOHCHNH₂COOH
But apparently this is incorrect (I seem to have gone wrong at the 3rd step going from H2C=CHCHBrCOOH CH3CHOHCHBrCOOH)
What exactly is wrong?

[AlirezaDehghani]

Hi
your second step involves the formation of a carbocation that would rearrange so the third product is wrong and it would be CH3CHCHCOOH.
I would suggest the following syntheses.
CH2OHCH2CH2COOH ^{conc H2SO4} CH3CHCHCOOH ^MCPBACH3C2H2OCOOH ^BF3,NH3CH3CHOHCHNH2COOH
the second step involves the formation of an epoxy and the third is the epoxy ring opening with NH3 and a Lewis acid.

[wildfyr]

Guys, use a chemical drawing system. If you are in school chemdraw is probably available, otherwise there are some free ones on the internet