Mechanism of the Formation of N,N-Dialkyl 2-Pyrrolecarboxamides from 1,3-Diketones and Dialkyl Oxaminoacetoacetamides
Paine, J.B. III, Brough, J.R., Butler, K.K., Erikson, E., and David Dolphin
J. Org. Chem.
The mechanism of formation of N,N-dialkyl-2-pyrrolecarboxamides I (R = Me, Et; R1 = MeCO, Me, Et) from the reaction between MeCOC(=NOH)CONR2 (II; same R) and MeCOCHR2COMe (III; R2 = H, Me, Et) upon treatment with Zn in AcOH differs from the analogous reaction between 2-(hydroxyimino)-3-oxoalkanoate esters and III. The 3-substituent of I is derived exclusively from II, not III. Parallel regioselectivity was observed in the reaction of 2-acylcycloalkanones IV (n = 3, 4; R3 = Me, Et) with II or with di-Et aminomalonate. The strong preference of IV (n = 3) for initial reaction at the exocyclic CO led to pyrrole-3-butanoic acids V (same R3) via ring opening. 2-Acyl-cyclohexanones, by contrast, gave good yields of a tetrahydroindole.