Use of excited-state and ground-state redox properties of polyoxometalates for selective transformation of unactivated carbon-hydrogen centers remote from the functional group in ketones
- Emory Univ., Atlanta, GA (United States)
Two types of processes are described which involve the selective transformation of unactivated carbon-hydrogen bonds in a ketone, cis-2-decalone, cis-1, which possesses conventionally far more reactive bonds. The first type of process involves irradiation of decatungstate, W{sub 10}O{sub 32}{sup 4{minus}} in the presence of cis-1 producing, trans-2-decalone, trans-1, the product resulting from epimerization of an unactivated tertiary C-H bond remote form the carbonyl group, in high selectivity at high conversion of substrate. The second type of reaction involves irradiation of the heteropolytungstate, {alpha}-P{sub 2}W{sub 18}O{sub 62}{sup 6{minus}} or {alpha}-PW{sub 12}O{sub 40}{sup 3{minus}}, in the presence of cis-1 producing two monounsaturated ketones (octalones) in high selectivity with the nonthermodynamic isomer, 2, in comparable or greater quantity than the conventional thermodynamic (conjugated) isomer, 3, eq 2. Both types of processes are independent of wavelength over the principal range of absorption of the complexes (:250-380 nm). The primary kinetic isotope of the corresponding decalin hydrocarbons were evaluated. The photochemical reaction of decatungstate with {alpha},{alpha},{alpha}{sup {prime}},{alpha}{sup {prime}}-D{sub 4}-cis-1 leads exclusively, even at moderate conversion of substrate (25%), to {alpha},{alpha},{alpha}{sup {prime}},{alpha}{sup {prime}}-D{sub 4}-trans-1. These data, an isotope crossover experiment in which decatungstate was irradiated in the presence of a 50/50 molar mixture of deuterated and protiated cis-decalin in CD{sub 3}CN are consistent with initial H atom abstraction in all cases. The dramatically different products seen with the different polyoxometalate systems are dictated by the relative rates of epimerization, oxidation, and escape of the cisoid tertiary bridgehead radicals in the initial radical cage and, to a lesser extent, by the rates of conventional radical-radical reactions and other processes.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 171650
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 3 Vol. 114; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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