Photocyclization of {alpha}-keto amides in homogeneous solution and aqueous cyclodextrin media. The role of zwitterions and diradicals in photoinduced electron transfer reactions
- Univ. of Rochester, NY (United States)
A mechanistic investigation of the photoreaction of the N,N-disubstituted benzoyl amides, PhCOCONR{prime}R{double_prime} (R{prime} = C{sub 2}H{sub 5}, R{double_prime} = Ph; R{prime} = R{double_prime} = C{sub 2}H{sub 5}; R{prime} = R{double_prime} = CH{sub 2}Ph; R{prime} = R{double_prime} = i-C{sub 3}H{sub 7}), in homogeneous solutions (water, methanol) and aqueous cyclodextrin is reported. The chief photoproducts, oxazolidin-4-ones, 3-hydroxyazetidin-2-ones, mandelamides and carbonyl compounds, can all be accounted for by a mechanism involving single electron transfer quenching of the {open_quotes}ketone{close_quotes} excited state with the amide serving as an electron donor. The first quenching product, a zwitterion Z{sub 1} undergoes rapid and irreversible decay to a diradical, D, and a second zwitterion, Z{sub 2}, by a sequence of proton transfer followed by a second intramolecular electron transfer. Formation of the observed products can be accounted for by decay or interception of D or Z{sub 2}. Although D and Z{sub 2} appear to be resonance contributors to a single structure, calculations suggest that their relative importance varies greatly with configuration, such that a {open_quotes}planar{close_quotes} structure is predominantly zwitterionic while partially or largely twisted structures should be predominantly diradical. The application of this principle leads to a consistent interpretation of the varied product distribution that occurs as substituents on the amide and the reaction medium are varied. 38 refs., 3 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 232293
- Journal Information:
- Journal of the American Chemical Society, Vol. 114, Issue 6; Other Information: PBD: 11 Mar 1992
- Country of Publication:
- United States
- Language:
- English
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