Thiol esters macrolactonization

Macrolactonization has been accomplished using Thiol and selenol esters can also be prepared in one pot from carboxylic acids using (1) reaction of the intermediate (2) with aromatic thiols or selenols is complete within a few minutes in DMF, while aliphatic thiols require a few hours. Formation of the phenylthiol ester of IV-Cbz-L-phenylalanine was accompanied by only slight racemization. N,N -Carbonyldi-sym-triazine can be used in place of (1), with similar results. 

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