THE FISCHER INDOLIZATION OF 4-ACETONYL-2,6-PIPERIDINEDIONES

Article abstract of DOI:10.1016/S0040-4020(01)85805-1

The PPA induced Fischer indolization of 4-acetonyl-2,6-piperidinediones 4 takes place both at the methylene and the methyl carbons, although the latter regioisomer (3) undergoes a further cyclization of the imide moiety upon the indole 3-position followed by ring-opening of the resulting intermediate 9 to give tetrahydrocarbazolone 8.Fragmentation of two possible regioisomers 3 and 7 to 2-methylindole occurs at higher temperatures.This process is more pronounced when using 4-acetonyl-3,4-dihydro-2(1H)-pyridone 13 as the substrate for the indolization.The use of N-acetylphenylhydrazone derivatives leads to similar results as a consequence of the deacylation of the initially formed indole derivatives.In this case, an additional C-acylation of the indole ring also occurs.