Indole-3-pyruvic acid oxime ethers and thieno analogues by heck cyclisation. Application to the synthesis of thia-tryptophans

Article abstract of DOI:10.1016/0040-4020(96)00909-X

N-allylation of N-BOC substituted o-iodo anilines (14a-e) and thienoamines (16,18,20) employing methyl or benzyl oxime ethers of ethyl (E)-2-oxo-5-bromo-3-pentenoate 2a, followed by palladium-catalysed Heck cyclisation yielded oxime ethers of Bz-substituted ethyl indole-3-pyruvates (15a-f) and thienopyrroles (17,19,21-23). Attempted conversion of 2a into the corresponding tosyl hydrazone or oxime resulted in formation of pyridazine (10) and oxazine (13) derivatives. The three possible isomers of thia-tryptophan were obtained as the ethyl esters from corresponding methyl oxime ethers by reduction of the oxime double bond.