Mechanistic investigations aided by isotopic labeling. 10. Investigations of novel furan-2,3-dione rearrangements by oxygen-17 labeling

Mechanism of rearrangement reactions of ketenimine–4-acylfuran-2,3-dione cycloadducts—a semiempirical molecular orbital study

“…*2 The structures of these heterocycles strongly depend on the nature of both the heterocumulene as well as the dione. For instance, the furandione 1 adds C,C-dimethyl-Nphenylketenimine 2 to yield compound 4, whereas from reaction of 1 with triarylketenimines the furo[3,2-c]pyridine 5 is obtained.2 To explain the observed reaction products an initial [4 + 21 cycloaddition between the ketenimine C=N double bond and the oxa-1,3-diene substructure of 1 to the primary cycloadduct 3, followed by a rearrangement sequence 3 +…”

“…Scheme 1pointed out that formation of 3 would represent the first example for this type of reaction of ketenimines. Isolation of4 …”

Investigation of Biosynthetic Pathways to Hydroxycoumarins During Post‐Harvest Physiological Deterioration in Cassava Roots by Using Stable Isotope Labelling

“…O enrichment of umbelliferone and esculetin: Following the literature procedure, [34,35] Feeding experiments with p-coumaric-2-13 C acid, caffeic-2-13 C acid and ferulic-2-13 C acid: By using the general feeding procedure, cassava roots (0.8 kg, cv MCOL 22) were peeled (0.64 kg) and divided into four groups, one as a control (40 g, the roots left to deteriorate for 3 and 4 days without feeding with any intermediates) and three equal groups (85 g), fed with p-coumaric-2-13 C acid, caffeic-2-13 C acid or ferulic-2-13 C acid (20 mg of each acid) dissolved in aq. 4 % Na 2 CO 3 (2 mL).…”

Synthetic methodologies in organic chemistry involving incorporation of [17O] and [18O] isotopes

“…The [ 17 O 2 ]‐labeled diketone dibenzoylmethane was prepared by isotope exchange reactions via hydration of the carbonyls with H 2 17 O in excess (~1 : 12) (Scheme a).…”