A Biomimetic Synthesis of Thiazolines Using Hexaphenyloxodiphosphonium Trifluoromethanesulfonate

Most chemical syntheses of thiazolines use serine residues, whereas nature employs cysteine residues. In a biomimetic approach, [(Ph3P+)2O](OTf−)2 was used to promote triphenylmethyl (Tr) deprotection and dehydrocyclization of simple cysteine N-amides to give thiazolines in excellent chemical and optical yields (see scheme). This mild method was extended to the synthesis of, for example, thiazolines from cysteine-containing dipeptides in high yield and without significant loss of chirality at the C2-exomethine carbon atom. TF=trifluoromethanesulfonyl, Cbz=benzyloxycarbonyl