Spectral studies on 1-substituted-3-(1-oxo-3-hydroxy-2-cyclohexene-2-yl)-4-oxo-4, 5,6,7-tetrahydroindoles — an unexpected mass spectral fragmentation
K Nagarajan S J Shenoy D R Müller W J Richterc L Kozerski V Pattabhi
Click here to view fulltext PDF
IR, UV, NMR and mass spectral data for the title compounds are discussed. The EI mass spectra of4. and the analogues5–9 and11–15 display major (M-Cn2H3O2)+ fragment ions that correspond to the loss of a structural element not present in the parent molecules. These (M-59)+ ions have no equivalent in the model compound l-phenyl-2,6,6-trimethyl-4-oxo-4, 5,6,7-tetrahydroindole (27). The unusual fragmentation is thought to be initiated by α-cleavage within the alicyclic 1,3-diketone moiety (ring C) under concomitant formation of a benzylic radical site. Reclosure of this ‘open’ intermediate to a lactone-type molecular ion provides two O-atoms in the proximity required for an ejection of a CH2COOH radical as the neutral species in question. The1H NMR spectra of4 and its methyl ether16 reveal restricted rotation of substituents at positions 1 and 3 of the pyrrole ring, the eight methylene protons becoming fully anisochronous at 500 MHz. X-ray studies on single crystals of8 confirmed its structure.
K Nagarajan1 2 S J Shenoy2 D R Müller W J Richterc3 L Kozerski4 V Pattabhi5
Volume 135, 2023
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode