One Heteroatom at a Ring Junction

Compound 79 and its 3-methyl analog were prepared from ethyl a-(2-pyridyl)glycinate with DMF-DMA, TOF, or DEMA [91JFIC1715, 91ZN(B)1110]. 

Derivatives of the pyrrolooxazole were obtained either from Pro after reaction with phenylglyoxal to give a mixture of isomers 80 (87TL6077) or from a pyroglutamic acid derivative [89H(29)2089], 

Reaction between D-Cys and an oxazoline aldehyde, prepared from l-Phe gave the bicyclic compound 83 [92H(34)903], A derivative of the same system was obtained from penicillamine with a functionalized AA (88CC1128). 

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