2-butene photoreactions

Similar product ratios were reported for the methyl pyruvate/2,3-dimethyl-2-butene photoreaction. In this case, however, a state selectivity effect is responsible for the formation of the different ether and alcohol products [31]. Obviously the existence of allylic hydrogens favors the formation of unsaturated acyclic products via hydrogen migration steps at... 

Figure 5. Programmed temperature gas chromatogram of photoreaction products of phenylazide with 3-methyl-l-butene in benzene...

Previously, Ohashi and his co-workers reported the photosubstitution of 1,2,4,5-tetracyanobenzene (TCNB) with toluene via the excitation of the charge-transfer complex between TCNB and toluene [409], The formation of substitution product is explained by the proton transfer from the radical cation of toluene to the radical anion of TCNB followed by the radical coupling and the dehydrocyanation. This type of photosubstitution has been well investigated and a variety of examples are reported. Arnold reported the photoreaction of p-dicyanobenzene (p-DCB) with 2,3-dimethyl-2-butene in the presence of phenanthrene in acetonitrile to give l-(4-cyanophenyl)-2,3-dimethyl-2-butene and 3-(4-cyanophenyl)-2,3-dimethyl-l-butene [410,411], The addition of methanol into this reaction system affords a methanol-incorporated product. This photoreaction was named the photo-NO-CAS reaction (photochemical nucleophile-olefin combination, aromatic substitution) by Arnold. However, a large number of nucleophile-incorporated photoreactions have been reported as three-component addition reactions via photoinduced electron transfer [19,40,113,114,201,410-425], Some examples are shown in Scheme 120. 

Whether the role of the second olefinic partner is catalytic or a triplex intermediate is involved is not yet clear. The role of triplexes in photoreactions of aromatic compounds with olefins may be even more complex. For example, excited biphenyl forms both a fluorescent dual and triple exciplex with 2,3-dimethyl-2-butene [120]. The possibility of these two pathways of deactivation can explain the inefficient photocycloaddition in the particular case of 1biphenyl /cyclopentene [121]. 

The photoreactions of 3-ethoxyisoindolenone with 1,1-dimethoxyethene, tetra-methylethylene, and cts-2-butene in methylene chloride solvent were chosen for quantum yield studies50, s9 With 0.06 M 1,1-dimethoxyethene the quantum yield of cycloadduct formation is 0.72, and with 0.06 M tetramethylethylene the total quantum yield of adduct formation is 0.59. Over the concentration range 0.06—2.00 M, the quantum yields of product formation from addition to 1,1-dimethoxyethene and tetramethylethylene are inversely related to the olefin concentration. Plots of reciprocal of quantum yield of product formation vs. reciprocal of olefin concentration one non-linear however, plots of reciprocal of quantum yield vs. olefin concentration are linear with slopes and intercepts as shown in Table 5. For photoaddition of 3-ethoxyisoindolenone to tetramethylethylene and c/s-2-butene, the product ratios (56 57 58 and 59 60 61 62) are independent of olefin concentra-... 

Photoreactions of [Cr(CO)3( /6-C7H8)] (41) with 6-mono- and 6,6-disub-stituted pentafulvenes (59a-59f) preferentially yield dicarbonyl complexes with substituted tj3 5-2-cyloheptadienylene-2-cyclopentadienylidenemethane chelate ligands (82,83). In the course of the reaction, C-6 of the fulvene forms a C—C bond to C-l of the 1,3,5-cycloheptatriene ligand, and one CO ligand is displaced. This reaction is of the same type as the formation of the f/3 5-[ 1 -(3-butene-1,2-diyl)-7-isopropylidenecycloheptadienyl] complexes 47c, 47e and 47t. The fulvene unit is transformed into a monosubstituted cyclo-pentadienyl entity, / -coordinated to the chromium, with the 1,3,5-cyclo-... 

Carless has reported a careful study of the photoreaction between acetone and 2,3-dimethyl-2-butene 127>. Together with photoreduction products and oxetane are formed two alcohols which can be explained simply as internal disproportionation products of the diradical. 

In the photoreaction of 2-cyanonaphthalene with 2,3-dimethyl-2-butene in methanol, McCullough proposed that a key step of this photoreaction is a radical coupling between the radical anion of 2-cyanonaphthalene and the radical cation of 2,3-dimethyl-2-butene [170]. The zwitter ionic intermediate thus produced reacts then with methanol (Scheme 63). In the photoreaction of 9-cyanophenanthrene with 2,3-dimethyl-2-butene in methanol, Pac proposed that a nucleophile adds first to the radical cation of the alkene to produce the radical species which then reacts with the radical anion of 9-cyanophenanthrene [171]. Protonation of the anion gives the solvent-incorporated adduct (Scheme 64). In the photoreaction of l-cyano-2,3-diphenylethene with 2,5-dimethyl-2,4-hexadiene in methanol, Lewis proposed that a key step of this photoreaction is a... 

The aminocyclopropane derivative 374 and the propellane 372 were obtained, each in 26 % yield, by photocycloaddition of 370 and ethylene in acetone . Diradicals 371 and 373 were suggested as intermediates in the photoreaction (equation 90). The use of isobutene or 2,3-dimethyl-2-butene instead of ethylene gave no cyclopropane product . 

The authors have tried the method to apply photoreaction of metal carbonyl on solid surface for preparation of catalysts, and have found that metal carbonyls, M(CO)g(M=Mo, W), adsorbed on porous Vycor glass are activated as catalysts by their irradiation with UV light in the presence of reactants (20). Fig.6 shows a time course of the propene reaction carried out on the Mo(CO)g-, W(CO)g- or Cr(CO)g-adsorbed porous Vycor glass(denoted by Mo(CO)g/PVG, etc., hereafter). No reaction occurs under darlc. Propene is converted to equal molar amounts of ethene and butene under the irradiation of Mo(CO)g/PVG and W(CO)g/PVG, but no activation of Cr(CO)g/PVG has been observed. This result indicates the photoinduction of the catalytic activity of Mo(CO)g/PVG and W(CO)g/PVG for the metathesis of propene. The reaction continues for about 30 min even after the stop of the... 

As described above, the photoaddition of MeOH to 1,1-diphenylethene in the presence of methyl p-cyanobenzoate gave 2,2-diphenylethyl methyl ether, the Type I product [13]. Hixson reported the photoinduced intramolecular charge-transfer of 3-(p-cyanophenyl)-l-phenylpropene followed by the MeOH-addition [29]. On the other hand, McCullough et al. reported that the photoreaction of 2-naphthonitrile with 2,3-dimethyl-2-butene in the presence of MeOH gave the Type //products [30]. In 1978, Mazzocchi et al. [31] and Kubo and Maruyama [32] published the first reports on the PPA reaction using phthalimides which formed the Type II products. Mariano et al. reported the PPA reaction using pyrrolinium salts as A, leading to Type //product [33]. Type///product, for example, was found in the CNN-photosensitized reaction of indene with H O [34]. 

Coyle has summarized the photochemistry of carboxylic acid derivatives. For arene carboxylic acid esters it has been shown that [2-1-2]-cycloaddition competes with hydrogen abstraction by the excited ester from an allylic position of the alkene. The addition of methyl benzoate 17 to 2-methyl-2-butene gave a 1 1 mixture of the Paterno-Bilchi adduct 18 and the coupling product 19. Less electron-rich alkenes (e.g., cyclopentene) did add preferentially toward the benzene ring of 17 in an ortho- and metacycloaddition manner. Furans could also be added photochemically to methyl benzoate and other aren-ecarboxylic acid esters. The resulting bicyclic oxetanes could be transformed into a series of synthetically valuable products. [2-1-2]-Cycloadducts and/or their cleavage or rearrangement products have also been described for photoreactions of alkenes with diethyl oxalate,benzoic acid, " and carbamates. ... 

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