A photochemical route to vinylglycine and a vinylglycine dipeptide

Enantiomerically pure vinylglycine (4b) can be prepared from natural („chiral pool”︁) amino acids by photoelimination of γ‐functionalized N‐phthaloyl amino acid esters. Two routes have been developed: (a) a three‐step synthesis of substrate 3b [PhtN‐Met(SO)OMe] from (S)‐methionine and subsequent photolysis, (b) the use of N‐phthaloyl activated methyl 2‐amino‐4‐chloro‐ or ‐4‐bromobutanoates 3d, e which are available from (S)‐methionine (four‐step synthesis) or from (S)‐homoserine (two‐step synthesis). The photoelimination (of HOSMe from 3b and of HX from 3d, e) proceeds quantitatively and leads to N,C‐protected vinylglycine 4a in high yields. This strategy could also be applied to peptide‐bound substrates as was shown for the protected Met‐Gly (5b) which was transformed into the N‐protected vinylglycine‐glycine dipeptide 6 in three steps.