I do have both the amine and acid of my amino acid protected as a boc and methyl ester respectively.
I have in fact made an unnatural amino acid containing a benzaldehyde. It is this aldehyde i am looking to carry out my Wittig reaction on, coupling it with a very similar amino acid which will be my ylide. Essentially i wish to form a cis-stilbene between two amino acids derived from phenylalanine.
If i can understand a little more precisely the pKa of the alpha proton it may help me in choosing the correct base, currently i suspect the pKa is in the region of 18-25 but it would be great if i have some actual literature where this had been calculated.
I appreciate the previous comments I hope my problem is a little clearer.