Dye-sensitized Photooxygenation Research Articles

The dye-sensitized photooxygenation of hemopyrrole.

Die durch Rose Bengal sensibilisierte Photooxygenierung des Kryptopyrrols in Methanol ergab Athylmethylmaleimid, 4-Athyl-5-methoxy-3,5-dimethyl-3-pyrrolin-2-on, 4-Athyl-5-hydroxy-3,5-dimethyl-3-pyrrolin-2-on und 4-Athyl-3-hydroxy-3,5-dimethyl-4-pyrrolin-2-on.

The Dye-sensitized Photooxygenation of Hexamethyleneammonium Hexamethylenedithiocarbamate by Xanthene Dyes

Abstract The photoelimination of hexamethyleneammonium hexamethylenedithiocarbamate (HMTC) can be sensitized by xanthene dyes, such as rose bengal and eosine yellowish. In contrast to the direct photolysis results, the presence of HMTC in the dye-sensitized decomposition produces no carbon disulfide and consumes oxygen during the irradiation. The quantum yield of photoelimination in an aerated ethanol solution was measured. The quantum yield was almost unchanged on the variation of the xanthene dye concentration from 10−5 to 10−6m. This is different from the former observation that there was an apparent tendency for the quantum yield to decrease monotonously with an increase in the thiazine dye concentration. The singlet oxygen mechanism, in which the photochemical reaction is initiated by the interaction between the triplet dye and the ground-state oxygen molecules, has been inferred for the dye-sensitized photoelimination of HMTC. It has been explained in terms of the effect of 1,4-diazabicyclo [2.2.2] octane, β-carotene, and tetramethylethylene in reducing the quantum yield. The photooxygenation of HMTC by dyes seemed to be caused by attack of the singlet oxygen on the thiocarboxyl-ion group, which has a rate constant of 108m−1sec−1 in ethanol.

The photosensitised oxygenation of 3-methylpyrrole involving a dioxetan intermediate

The dye-sensitised photo-oxygenation of 3-methylpyrrole in methanol gives 3-methyl-3-methoxy-Δ4-pyrrolin-2-one and 3-hydroxy-3-methyl-Δ4-pyrrolin-2-one (which we assume arise via a dioxetan intermediate) as well as 3-methyl-5-methoxy-Δ3-pyrrolin-2-one, 4-methyl-5-methoxy-Δ3-pyrrolin-2-one, 5-hydroxy-3-methyl-Δ3-pyrrolin-2-one, and citraconimide.

Photoinduced reactions—LIX: Reactivity of singlet oxygen toward methoxybenzenes

The dye-sensitized photooxygenation of a series of methoxybenzenes (Ia-Ie) in methanol has been investigated. Highly substituted methoxybenzenes (Ig, Ii-Il) were susceptible to photooxygenation, while less substituted methoxybenzenes (Ia-Ig, Ih) were found to be unreactive under similar conditions. The participation of singlet oxygen in the reaction was elucidated by photooxygenation using sensitizers having different triplet energies and by quenching experiments. Relative reaction rates of methoxybenzenes with singlet oxygen were shown to correlate with their half-wave oxidation potentials (E 1 2 ) and with their charge-transfer maxima ( v c.t. ) with tetracyanoethylene.

Formation of 1,4-endoperoxides from the dye-sensitized photo-oxygenation of alkyl-naphthalenes

1,4-Endoperoxides are formed in the dyesensitized photo-oxygenations of 1,4-dimethylnaphthalene (Ia), 1,8-dimethylnaphthalene (Ib), 1,4,5-trimethylnaphthalene (Ic), 1,2,4-trimethylnaphthalene (Id), and 1,2,3,4-tetramethylnaphthalene (Ie).

The dye-sensitized photooxygenation of 2-ethylidenebicyclo[2.2.1]hept-5-ene

The mode of singlet oxygen attack on norbornene derivatives was probed via a study of the dye-sensitized photooxygenation of 2-ethylidenebicyclo[2.2.1]hept-5-ene ( 1). Reduction of the resulting allylic hydroperoxides provided the epimeric 2-hydroxy-2-vinylbicyclo[2.2.1]hept-5-enes ( 2 and 3) and 2-(1-hydroxyethyl)bicyclo[2.2.1]hept-2,5-diene ( 4), the relative yields of which were apparently controlled by steric factors. Also isolated were two novel multicyclic ketones, 5 and 6, derived from thermal rearrangements of the primary oxidation products.

Pyrrole photo-oxidation. Unusual products from 2,5-dimethylpyrrole

The dye-sensitised photo-oxygenation of 2,5-dimethylpyrrole in methanol yields the dealkylation products 5-methoxy-5-methyl-Δ3-pyrrolin-2-one and 5-methoxy-5-methoxymethyl-Δ3-pyrrolin-2-one in addition to the surprising structure, 2-formyl-2-methoxy-5-methylidene-Δ3-pyrroline; similar photo-oxidation of 2-methylpyrrole gives 5-methoxy-5-methyl-Δ3-pyrrolin-2-one as the major product.

The dye-sensitized photooxidation of cyclopentadiene

The dye-sensitized photooxygenation of cyclopentadiene provides a novel one-step synthesis of 4,5-epoxy- cis-2-pentenal ( 3) and cis-1,2:3,4-diepoxycyclopentane ( 4) presumably via a facile thermal isomerization of the transannular peroxide ( 1). Spectrometric identification of the cis- and trans-epoxy- aldehyde is presented. Some unique transformations of 3 are described. For example, 4,5-epoxy- cis-2- pentenal undergoes a facile acid-catalyzed rearrangement in aqueous solutions to furfuryl alcohol. As a dienophile, 3 produces an adduct with cyclopentadiene and ethyl vinyl ether. Hydrogenation of 3 with Raney nickel in methanol provides 5-hydroxypentanal ( 8) and 1,5-pentanediol. Hydrogenolysis of 3 with Raney nickel in aqueous solutions at higher pressure affords 1,5-pentanediol in 61% yield. In a novel thermal process, the epoxyaldehyde fragments to furan and formaldehyde.

Photoinduced reactions. XLIV. Reactivity of singlet oxygen toward methoxybenzenes.

Abstract The dye-sensitized photooxygenation of a series of methoxybenzenes (Ia-Ie) in methanol has been investigated. Highly substituted methoxybenzenes (Ig, Ii-Il) were susceptible to photooxygenation, while less substituted methoxybenzenes (Ia-Ig, Ih) were found to be unreactive under similar conditions. The participation of singlet oxygen in the reaction was elucidated by photooxygenation using sensitizers having different triplet energies and by quenching experiments. Relative reaction rates of methoxybenzenes with singlet oxygen were shown to correlate with their half-wave oxidation potentials (E 1 2 ) and with their charge-transfer maxima ( v c.t.) with tetracyanoethylene.

Evidence for the participation of 1G + and 1.DELTA.g oxygen in dye-sensitized photooxygenation reactions. II

Evidence for the participation of 1G + and 1.DELTA.g oxygen in dye-sensitized photooxygenation reactions. II

Evidence for the participation of 1.SIGMA.g+ and 1.DELTA.g oxygen in dye-sensitized photooxygenation reactions. I

Evidence for the participation of 1.SIGMA.g+ and 1.DELTA.g oxygen in dye-sensitized photooxygenation reactions. I