Direct selective acylation of an unactivated carbon-hydrogen bond in a caged hydrocarbon. Approach to systems for carbon-hydrogen bond functionalization that proceed catalytically and selectively at high substrate conversion

Abstract

We have found that the HMQC NMR technique in a onedimensional format11 can be used to visualize the methylene protons directly bonded to the labeled allylic 13C carbon atom of metabolite 7, without interference from matrix resonances arising from protons attached to 12C and natural abundance 13C carbon atoms. The same metabolite sample as illustrated in Figure lb was analyzed with a Varian VXR 500 FT NMR spectrometer equipped with an indirect-detection probe. Acquisition of the HMQC carbon-coupled proton spectrum (Figure lc) was completed in 6 h, much less than the time required for a conventional proton-coupled 13C NMR spectrum. The methylene protons attached to the 13C-labeled carbon of 7 appear as a doublet of multiplets centered about 4.53 ppm (7CH = 148.5 Hz), while the HOD and other extraneous peaks are completely filtered out.Acquisition with WALTZ carbon decoupling eliminated one-bond heteronuclear coupling and provided the expected single multiplet at 4.53 ppm (Figure Id). These spectra unambiguously confirm the structure of the isotopically labeled metabolite 7, enabling us to demonstrate that trichloroacrolein (2) is generated metabolically from triallate (1). Further studies elucidating the in vitro and in vivo metabolic pathways of triallate xenobiotic metabolism are in progress and will be reported in detail elsewhere.In conclusion, we have shown that the proton-detected HMQC 13C NMR experiment can be used to elucidate metabolite structures on a sample scale previously unattainable by conventional NMR techniques. This method provides important data on proton connectivity and heteronuclear coupling in the context of a simple experimental design which has the advantages of matrix transparency as well as greatly enhanced sensitivity relative to ordinary 13C NMR spectroscopy. We anticipate that the HMQC l3C NMR experiment will complement mass spectrometry as a major research tool in metabolism chemistry.Acknowledgment. We thank Dr. Sastry Kunda for providing us with samples of isotopically labeled triallate.(11) Applied with a nonincremental evolution time of 0.

Tandem Intramolecular Hydroalkoxylation–Hydroarylation Reactions: Synthesis of Enantiopure Benzofused Cyclic Ethers from the Chiral Pool

“…However, this rarely produces high chemical conversion, either because of a rapid drop in the alkyl radical concentration after a few percent conversion (due to reaction with the persistent reduced tungstate), or because of the catalyst consumption when an easily oxidized radical is used. Useful reactions are obtained when the radical is trapped efficiently by a path that regenerates the catalyst,36 as is indeed the case for oxygenation, which can be carried out to a rather high level of conversion (>50 %) 6. In the present case, the alkene serves the same function as oxygen: it both traps the radicals and regenerates the catalyst (in this case indirectly, via the radical adduct as shown in the cycle in Scheme ).…”

Photocatalytic and catalytic activity of heterogenized W10O324− in the bromide-assisted bromination of arenes and alkenes in the presence of oxygen

“…It is generally accepted that illumination of this polyoxoanion leads to the formation of a charge transfer excited state, which, in few ps, decays to an extremely reactive transient referred as wO (Scheme 1) [13][14][15]. Previous studies [13][14][15][16][17][18][19][20][21][22][23] indicate that the intermediate wO is able to initiate the oxidation of the substrate (RH) through either hydrogen abstraction or direct electron transfer to give, in any case, the same one-electron reduced species of the decatungstate. The substrate-derived radical, thus obtained, in the presence of Scheme 1.…”

Photoinduced Generation of Superoxidants for the Oxidation of Substrates with High C−H Bond Dissociation Energies

“…TBADT, which serves as an efficient photocatalyst, can induce C−H activation followed by the reaction with a suitable substrate as radical acceptors, which leads to new C−C bond formation . Michael acceptors, carbon monoxide and nickel species were used as alkyl radical traps in TBADT promoted radical addition to nitriles, alkenes and acetylene . The photoexcited state of TBADT is a strong oxidant because the radical addition of C−H bond across the C=N bond is possible .…”