protonation of 5-aminooxazole leading to the electrophilic iminium salt; 2) trapping of the iminium species by the neighboring C-terminalcarboxylicacid leading to a putative spirolactone; and 3) intramolecular nucleophilic addition of the tethered alcohol to the spirolactone followed by fragmentation. The strategically incorporated 5-aminooxazole serves as an internaltracelessactivator of the neighboring
A three-component reaction of an alpha,alpha-disubstituted alpha-isocyanoacetamide, an aldehyde and an amino alcohol afforded the 5-iminooxazoline, which, upon saponification, cyclized under acidic conditions to provide the macrocyclodepsipeptide in good overall yield.
US2229744
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Activation of a Terminal Carboxylic Acid by an Internal Oxazole: A Novel Synthesis of Macrocyclodepsipeptide
macrocyclodepsipeptides fromsimple and readily available starting materials has been developed. The sequence consists of (a) a three-component reaction of an aldehyde, an amino alc., and a dipeptide isocyanate and (b) a domino process involving an activation of the terminal carboxylic acid function by a built-in aminooxazole followed by a macrocyclization under acidic conditions. The synthesis is atom-economic