How to convert ethanal to 2-hydroxy-3 butenoic acid?

How to convert ethanal to 2-hydroxy-3 butenoic acid?


I tried crossed aldol condensation with formaldehyde followed by acid addition.After that how should I proceed ?




[![enter image description here](https://i.stack.imgur.com/OJQ9b.png)](https://i.stack.imgur.com/OJQ9b.png)


Once you have got your acrolein from the aldol condensation of ethanal and formaldehyde you can react it with $\ce{NaCN, HCN}$ under kinetic control to get direct addition of the cyanide to the enone, forming a cyanohydrin[[1]](https://books.google.co.uk/books?id=kQgu2j_ber0C&pg=PA504&lpg=PA504&dq=direct+addition+of+cyanide+to+enone&source=bl&ots=AoR2Q3Hckh&sig=EZG3Eftl_bs7G1e-777Wmm7VegQ&hl=en&sa=X&ved=0ahUKEwja6ZmhjfXMAhVqAsAKHUOyDNgQ6AEIPDAF#v=onepage&q=direct%20addition%20of%20cyanide%20to%20enone&f=false). The nitrile can then be hydrolysed in aqueous acid to yield the carboxylic acid.


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