Visible-Light-Driven Epoxyacylation and Hydroacylation of Olefins

Article Cite This: J. Org. Chem. 2018, 83, 8331−8340

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Visible-Light-Driven Epoxyacylation and Hydroacylation of Olefins Using Methylene Blue/Persulfate System in Water Gabriela F. P. de Souza,† Juliano A. Bonacin,‡ and Airton G. Salles, Jr.*,† †

J. Org. Chem. 2018.83:8331-8340. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 08/17/18. For personal use only.

Department of Organic Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, Campinas, São Paulo, 13084-862, Brazil ‡ Department of Inorganic Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, Campinas, São Paulo, 13084-862, Brazil S Supporting Information *

ABSTRACT: A visible-light-driven strategy for hydroacylation and epoxyacylation of olefins in water using methylene blue as photoredox catalyst and persulfate as oxidant is reported. In this unprecedented unified approach, two different transformations are accomplished using only one set of reagents. The method has a broad scope spanning a range of aromatic and aliphatic aldehydes as well as conjugated and nonconjugated olefins to deliver ketones and epoxyketones from abundant and inexpensive chemical feedstocks.

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INTRODUCTION Photoredox catalysis has come to light in the past few years as a powerful tool to the development of a broad range of new bond-forming reactions.1 In spite of substantial advances in the field of photocatalytic activation of Csp3−H bonds,2 the visiblelight-mediated selective activation of Csp2−H bonds has remained somewhat underexplored.3 In this context, cheap and commercially available aldehydes would be representatives for the mild generation of acyl radicals. The resulting radical intermediates can promptly engage into several transformations expanding molecular complexity in an atom-economical fashion. As a prominent example, the addition of acyl radicals to olefins converts abundant chemical feedstocks into ketones and α,β-epoxy ketones, which are relevant precursors for chemical transformations.4 However, previously reported methods suffer from limited substrate scope (usually the combination of electron-poor olefins and aromatic aldehydes), harsh reaction conditions, and the use of expensive transition metals as catalysts.5 Regarding the photocatalytic alternative, to date, few reports can be found.6 Furthermore, these methods are somewhat hampered by the use of UVA irradiation, transition metals, and once again, narrow substrate scope (Scheme 1). A practical guiding principle of Green Chemistry is the capability to conceive benign chemical transformations from the very beginning. As Sheldon stated, “Green Chemistry is primary pollution prevention rather than waste remediation”.7 A lot of effort has been devoted in the design of environmentally suitable protocols encompassing issues such as atom efficiency, energy consumption, and sustainability of chemical procedures.8 Despite the inherent green features of © 2018 American Chemical Society

photocatalysis, the development of methods employing alternatives to organic solvents and transition metal-based photocatalysts, so ubiquitous in the well-established approaches, is still highly desirable. Ticking all the boxes of sustainable chemistry, water-soluble organic dyes are increasingly attracting the attention of the synthetic community as photocatalysts because of their advantages of being less toxic, low-cost, and easily accessible.9 Motivated by the desire to develop a more sustainable photochemical protocol to perform hydroacylation/epoxyacylation of olefins, we focused our attention on the use of methylene blue as a water-soluble organic photocatalyst. Herein, we describe a visible-light-driven hydroacylation and epoxyacylation of nonconjugated and conjugated olefins, with aliphatic and aromatic aldehydes using potassium persulfate and methylene blue as an organophotoredox catalyst. The reaction was carried out in pure water, and depending on the nature of the olefin, two different reaction pathways operate, leading to ketones or α,β-epoxyketones in moderate to high yields. Isolation of compounds was performed employing a plug of silica, therefore, preventing a large waste generation.

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RESULTS AND DISCUSSION As an initial design, we chose the reaction between styrene and benzaldehyde as a representative transformation (Table 1, entry 1). By using 2.5 mol % of methylene blue as photocatalyst along with potassium persulfate (2 equiv) as oxidant in basic aqueous solution under 100 W irradiation, Received: April 23, 2018 Published: July 6, 2018 8331

DOI: 10.1021/acs.joc.8b01026 J. Org. Chem. 2018, 83, 8331−8340

Article

The Journal of Organic Chemistry Scheme 1. Previous Work and Our Approach for Epoxyacylation/Hydroacylation

targeted product in 92% yield with an excellent diastereomeric ratio (trans/cis > 95:5, determined by 1H NMR). Interestingly, under the optimized conditions, we did not observe the corresponding hydroacylation product. In spite of the photosensitizing ability of methylene blue, we also did not observe any identifiable product coming from singlet oxygen reactions. As the reaction medium is air-equilibrated, we believe the oxygen concentration in water is not enough to allow substantial singlet oxygen generation. Control experiments demonstrated that all the reagents and light were essential to obtain considerable conversion to 3a (Table 1, entries 7−10). To probe the engagement of O2 in the process, we performed the reaction in degassed water and kept the aqueous medium under a N2 atmosphere, which led to a lower yield (Table 1, entry 11), suggesting an important role of oxygen in this transformation. We also investigated the use of acetonitrile as solvent, and under this condition, yield was very low (Table 1, entry 12). In our protocol, an organic suspension in water is formed and a fast stirring speed (1150 rpm) is of paramount importance to guarantee acceptable yields. After establishing the optimized conditions for our protocol, we then explored the substrate scope employing a range of aldehydes and olefins (Scheme 2). Electron-donating and electron-withdrawing substituents on the phenyl ring of both aldehyde and olefin were found to be competent substrates in this transformation, furnishing the corresponding epoxyketones in good to excellent isolated yields (Scheme 2, 3a−3i, 3k, 3l, 3n). Notably, the reaction between an aliphatic aldehyde (cyclohexanecarbaldehyde) and styrene was successfully performed in good yield (Scheme 2, 3j). 2-Vinylpyridine

Table 1. Optimization of the Visible-Light-Driven Epoxyacylationa

entry 1 2 3 4 5 6 7 8 9 10b 11c 12

methylene blue (mol %) 2.5 2.5 2.5 2.5 5.0 2.5 2.5 2.5 2.5 2.5 2.5

base (mol L−1) K2CO3 (1.0) K2CO3 (1.5) K2CO3 (0.5) K2CO3 (0.5) K2CO3 (0.5) NaOH (0.5) K2CO3 (0.5) K2CO3 K2CO3 K2CO3 K2CO3

(0.5) (0.5) (0.5) (0.5)

K2S2O8 (equiv) 2.0 1.0 1.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

solvent

yield (%)

water water water water water water water water water water water water

35 26 47 92 72 25 10 traces 0 14 65 38

a

General conditions: 7 mL of water, 1 (1 mmol), 2 (2 mmol), visible light (100 W household bulb), 25 °C, 12 h. Yield of isolated product. b No light. cN2 atmosphere.

35% of the epoxyketone 3a was formed. Increasing the concentration of base and decreasing the oxidant loading to 1.0 equiv led to inferior yield (Table 1, entry 2). To our delight, decreasing the concentration of base to 0.5 M and using 2 equiv of potassium persulfate gave access to the 8332


Article

The Journal of Organic Chemistry Scheme 2. Scope of the Visible-Light-Driven Epoxyacylationa

General conditions: 7 mL of water, 1 (1 mmol), 2 (2 mmol), visible light (100 W household bulb), 25 °C, 12 h. Yields of isolated products. Diastereomeric ratios were found greater than 95:5 (trans/cis) in each case as determined by 1H NMR.

a

with benzaldehyde smoothly underwent the reaction, leading to the corresponding epoxyketone in high yield (Scheme 2, 3m). This outcome indicates that our process is robust in the presence of a nitrogen-based compound. Next, we extended our method to nonconjugated olefins and benzaldehydes. Interestingly, the reaction between 1-decene and benzaldehyde gave ketone 5a in 35% yield (Table 2, entry 1). Long-chain ketones represent a class of compounds that might play a useful role in energy science as fuels10 and in medicinal chemistry as hypocholesterolemic agents;11 hence, we decided to reoptimize the reaction conditions to provide a range of these products in acceptable yields. We tested different reagent stoichiometries and observed that decreasing the amount of potassium persulfate, increasing the concentration of base, and decreasing the photocatalyst loading afforded 5a in 61% yield (Table 2, entries 2−7). Gratifyingly, using 1 equiv of potassium persulfate, 2.5 M as base concentration, and 0.5 mol % of methylene blue under 100 W irradiation provided 5a in 89% yield. Again, we performed the reaction in degassed water and kept the aqueous medium under a N2 atmosphere. This condition led to a lower yield (Table 2, entry 13) and advocates the important role of oxygen also in this transformation. The scope of the transformation was then evaluated. Electron-donating and electron-withdrawing substituents on the benzaldehyde aryl moiety together with different size longchain olefins were all well-tolerated, affording the corresponding ketones in moderate to excellent yields (Scheme 3, 5a−5i). Unfortunately, aliphatic aldehydes led to inconsistent results,

Table 2. Optimization of the Visible-Light-Driven Hydroacylationa

entry 1 2 3 4 5 6 7 8 9 10 11 12b 13c 14

methylene blue (mol %) 2.5 2.5 1.2 1.2 1.2 1.2 1.2 0.5 0.5 0.5 0.5 0.5 0.5

base (mol L−1) K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3

(0.5) (1.0) (1.0) (2.0) (2.0) (2.0) (2.5) (2.5) (2.5)

K2CO3 K2CO3 K2CO3 K2CO3

(2.5) (2.5) (2.5) (2.5)

K2S2O8 (equiv) 2.0 2.0 2.0 2.0 3.0 1.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0

solvent

yield (%)

water water water water water water water water water water water water water acetonitrile

35 47 40 55 23 61 50 89 8 traces 0 traces 50 0

a

General conditions: 7 mL of water, 4 (1 mmol), 4 (2 mmol), visible light (100 W household bulb), 25 °C, 12 h. Yield of isolated product. b No light. cN2 atmosphere.

and as such, we concluded that these substrates are not suitable for this transformation. Submitting styrenes (styrene, 1-chloro4-vinylbenzene, and 1-methoxy-4-vinylbenzene) to the opti8333


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The Journal of Organic Chemistry Scheme 3. Scope of the Visible-Light-Driven Hydroacylationa

General conditions: 7 mL of water, 4 (1 mmol), 2 (2 mmol), visible light (100 W household bulb), 25 °C, 12 h. Yields of isolated products.

a

pathway. Interestingly, the presence of (A) suggests a faster reaction with an oxygenated species other than TEMPO and then the subsequent formation of TEMPO adduct. At this stage, we hypothesized whether epoxidation of styrene could provide styrene oxide, followed by acyl radical ring-opening reaction to giving access to (C) (Scheme 5, item 2). Trapping of (C) with TEMPO would furnish the adduct (A) we observed in mass spectrometry. In order to confirm or exclude this hypothesis, we performed a test where styrene was replaced by commercial styrene oxide under the optimized conditions to check if epoxyketone 3a could be obtained (Scheme 5, item 2). After 12 h, 3a was not observed and only the diol coming from styrene oxide ring-opening reaction along with several unidentifiable byproducts was formed, thus excluding this hypothesis. Next, we hypothesized that the hydroperoxyl radical generated in the reaction medium would combine with (D) (which comes from acyl radical addition to the olefin), leading to the corresponding peroxide (E) (Scheme 5, item 3; see the Supporting Information for further discussion). Homolytic cleavage of (E) occurs, and subsequent trapping with TEMPO accounts for the observed product (A). Indeed, Watts et al.12 demonstrated that persulfate rapidly decomposes to hydroperoxide anion and sulfate at basic pH (Scheme 5, item 3). Hydroperoxyl radical could then be produced by electron transfer from hydroperoxide anion to methylene blue triplet (MB*) according to reports in the literature.13,14 Therefore, we believe there is stronger evidence corroborating this pathway. We also performed the reaction employing 1-decene and benzaldehyde under the optimized conditions in the presence of TEMPO. Complete inhibition of the transformation was observed with only the adduct (B) being detected by mass spectrometry (Scheme 6, item 1; see the Supporting Information for further details). To assess the influence of the electronics on the reactivity, we conducted experiments employing benzaldehydes bearing

mized hydroacylation conditions led to the corresponding epoxyketones in traces and recovery of starting materials unreacted. These results show that only nonconjugated, longchain olefins are likely to participate in the hydroacylation reaction. We also evaluated green chemistry credentials for our protocol using green metrics calculations. The values were superior in carbon efficiency and E-Factor when compared to other procedures reported in the literature for the same transformations and starting materials, thus demonstrating the improved sustainability of the method (see the Supporting Information for metrics definitions and calculations). To show the scalability of this transformation, we carried out a gram-scale reaction under sunlight irradiation (Scheme 4; see the Supporting Information for details). Gratifyingly, we obtained epoxyketone 3a in 84% yield after 6 h irradiation at room temperature. Scheme 4. Gram-Scale Preparation of 3a under Sunlight

Once the basic features of our methodology were explored, a series of experiments were conducted to gain mechanistic insight into the above transformation. First, we performed the reaction employing styrene and benzaldehyde under the optimized conditions, and TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) was used as a radical scavenger. The presence of TEMPO (2.0 equiv) completely inhibited the formation of the epoxyketone 3a. Instead, we observed the corresponding products of radical trapping, (A) and (B), by mass spectrometry (Scheme 5, item 1; see the Supporting Information for further details), clearly denoting a radical 8334


Article

The Journal of Organic Chemistry Scheme 5. Studies on the Mechanism

different substituents (Scheme 6, item 2; see the Supporting Information for details). The results showed that this transformation is more favorable for electron-rich benzaldehydes. It suggests that acyl radical addition to the olefin has an important role in the overall reaction rate, possibly because of polar effects.15 On the basis of the above experiments and literature precedence, we propose a plausible reaction mechanism for the transformation (Scheme 7, using styrene and benzaldehyde as representative substrates). Photoexcitation of methylene blue with a household light bulb (100 W) produces MB* as the triplet state electron acceptor. Because of MB* reduction potential (E1/2 = −0.062 V vs SHE),13 it engages in singleelectron transfer (SET) with the hydroperoxide anion (E1/2 = −0.88 V vs SHE)14 generated from persulfate alkaline hydrolysis to afford hydroperoxyl radical and methylene blue neutral radical (Scheme 7, step I; see the Supporting Information for control experiments and refs 12 and 13a). Acyl radical is then generated through hydrogen-atom transfer

(HAT) between benzaldehyde and hydroperoxyl radical (Scheme 7, step II). Indeed, hydrogen abstraction from aldehydes by oxygen-centered radicals is one of the most efficient methods of acyl radicals generation.15 The corresponding acyl radical then adds to the styrene to provide radical (D) which, followed by combination with hydroperoxyl radical (from step I, SET), gives access to the peroxide (E) (Scheme 7, steps III and IV). Finally, elimination of OH− from peroxide (E) under alkaline conditions leads to the targeted epoxyketone. Regeneration of methylene blue may occur through oxidation by oxygen in the air16 or even persulfate (it would explain why the transformation is still operating even under oxygen-free conditions; see Table 1, entry 11, and Table 2, entry 13). For the acylation reaction, a similar mechanism is proposed considering the lower amount of oxidant and photocatalyst employed in the optimized conditions (see the Supporting Information for further discussion). 8335


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The Journal of Organic Chemistry Scheme 6. More Studies on the Mechanism

Scheme 7. Proposed Reaction Mechanism

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CONCLUSION

oxidant. Pure water is the suitable solvent for this transformation. Electron-rich and electron-poor styrenes and benzaldehydes are all competent substrates for the epoxyacylation. Regarding the hydroacylation, long-chain nonconjugated olefins and several benzaldehydes are well tolerated in this transformation. The protocol can be carried out in gram-

In summary, we have developed a visible-light-driven hydroacylation and epoxyacylation of nonconjugated and conjugated olefins with a variety of aldehydes using methylene blue as an organophotoredox catalyst and potassium persulfate as an 8336


Article

The Journal of Organic Chemistry

(d, 1H, J = 1.96 Hz), 7.35−7.44 (m, 8H), 7.64 (dd, 1H, J = 7.83, 1.47 Hz). 13C NMR (100 MHz, Chloroform-d): δ 60.4, 62.9, 125.8, 127.1, 128.66, 128.99, 130.1, 130.4, 132.9, 135.2, 136.5, 196.3. (3-Chlorophenyl)(3-phenyloxiran-2-yl)methanone (3c). Prepared from styrene and 3-chlorobenzaldehyde following the general procedure A to give the product as a white solid (88% yield, 227.7 mg, mp = 85−87 °C). All data were consistent with those previously reported.17 1H NMR (500 MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.89 Hz), 4.24 (d, 1H, J = 1.89 Hz), 7.37−7.46 (m, 6H), 7.60 (d, 1H, J = 7.55 Hz), 7.90 (d, 1H, J = 7.55 Hz), 8.01 (s, 1H). 13C NMR (125 MHz, Chloroform-d): δ 59.5, 61.0, 125.8, 126.5, 128.4, 128.8, 129.2, 130.2, 133.9, 135.1, 135.3, 136.8, 192.1. (4-Chlorophenyl)(3-phenyloxiran-2-yl)methanone (3d). Prepared from styrene and 4-chlorobenzaldehyde following the general procedure A to give the product as a white solid (85% yield, 219.9 mg, mp = 123−125 °C). All data were consistent with those previously reported.5d 1H NMR (400 MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.00 Hz), 4.24 (d, 1H, J = 1.00 Hz), 7.36−7.43 (m, 5H), 7.47 (d, 2H, J = 8.30 Hz), 7.97 (d, 2H, J = 8.30 Hz). 13C NMR (100 MHz, Chloroform-d): δ 59.4, 61.1, 125.8, 128.8, 129.16, 129.24, 129.80, 133.7, 135.2, 140.6, 192.1. 3-Phenyloxiran-2-yl)(p-tolyl)methanone (3e). Prepared from styrene and 4-methylbenzaldehyde following the general procedure A to give the product as a pale yellow oil (89% yield, 212.1 mg). All data were consistent with those previously reported.18 1H NMR (500 MHz, Chloroform-d): δ 2.44 (s, 3H), 4.08 (d, 1H, J = 1.89 Hz), 4.29 (d, 1H, J = 1.89 Hz), 7.29 (d, 2H, J = 7.55 Hz),7.37−7.45 (m, 5H), 7.93 (d, 2H, J = 8.18 Hz). 13C NMR (125 MHz, Chloroform-d): δ 21.8, 59.3, 60.9, 125.8, 128.5, 128.7, 128.9, 129.5, 133.0, 135.6, 145.1, 192.6. (4-Methoxyphenyl)(3-phenyloxiran-2-yl)methanone (3f). Prepared from styrene and 4-methoxybenzaldehyde following the general procedure A to give the product as a white solid (90% yield, 228.9 mg, mp = 77−79 °C). All data were consistent with those previously reported.5d 1H NMR (400 MHz, Chloroform-d): δ 3.89 (s, 3H), 4.08 (d, 1H, J = 1.47 Hz), 4.26 (d, 1H, J = 1.47 Hz), 6.95 (d, 2H, J = 8.80 Hz), 7.36−7.43 (m, 5H), 8.01 (d, 2H, J = 8.80 Hz). 13C NMR (100 MHz, Chloroform-d): δ 55.5, 59.1, 60.8, 114.1, 125.8, 128.7, 128.9, 130.7, 135.7, 164.2, 191.3. Naphthalen-1-yl(3-phenyloxiran-2-yl)methanone (3g). Prepared from styrene and 1-naphthaldehyde following the general procedure A to give the product as a white solid (84% yield, 230.4 mg, mp = 109− 111 °C). All data were consistent with those previously reported.19 1H NMR (500 MHz, Chloroform-d): δ 4.17 (d, 1H, J = 1.26 Hz), 4.27 (d, 1H, J = 1.26 Hz), 7.41 (m, 5H), 7.50−7.66 (m, 3H), 7.91−8.07 (m, 3H), 8.68 (d, 1H, J = 8.80 Hz). 13C NMR (125 MHz, Chloroform-d): δ 59.7, 62.6, 124.3, 125.46, 125.83, 126.8, 128.54, 128.75, 128.88, 129.1, 130.2, 133.0, 133.8, 135.5, 196.2. (4-Fluorophenyl)(3-phenyloxiran-2-yl)methanone (3h). Prepared from styrene and 4-fluorobenzaldehyde following the general procedure A to give the product as a white solid (87% yield, 210.8 mg, mp = 82−84 °C). All data were consistent with those previously reported.20 1H NMR (400 MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.96 Hz), 4.31 (d, 1H, J = 1.96 Hz), 7.14−7.21 (m, 2H),7.36−7.45 (m, 5H), 8.05−8.11 (m, 2H). 13C NMR (100 MHz, Chloroform-d): δ 59.3, 61.1, 116.1 (d, JC,F = 22.0 Hz), 125.8, 128.8, 129.1, 131.2 (d, JC,F = 10.3 Hz), 131.8 (d, JC,F = 2.9 Hz), 135.3, 166.2 (d, JC,F = 256 Hz), 191.6. (3-Phenyloxiran-2-yl)(2-(trifluoromethyl)phenyl)methanone (3i). Prepared from styrene and 2-(trifluoromethyl)benzaldehyde following the general procedure A to give the product as a pale yellow oil (82% yield, 239.6 mg). 1H NMR (500 MHz, Chloroform-d): δ 3.94 (d, 1H, J = 1.26 Hz), 4.01 (d, 1H, J = 1.26 Hz), 7.30−7.44 (m, 5H),7.56− 7.79 (m, 4H). 13C NMR (125 MHz, Chloroform-d): δ 59.4, 62.7, 125.7, 125.9 (q, JC,F = 32.1 Hz), 126.8 (q, JC,F = 4.02 Hz), 131.8 (d, JC,F = 2.9 Hz), 128.1, 128.7, 129.1, 130.9, 131.7, 132.4, 134.7, 135.9, 198.1. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C16H12F3O2 293.0789; Found 293.0793. Cyclohexyl(3-phenyloxiran-2-yl)methanone (3j). Prepared from styrene and cyclohexanecarbaldehyde following the general procedure

scale under sunlight with no detrimental effect on yield. We believe this work will be of substantial interest to the synthetic community because of the unification feature represented by the range of substrates employed in two different transformations using only one protocol.

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EXPERIMENTAL SECTION

General Information. All reagents were purchased from commercial suppliers (Sigma-Aldrich, Oakwood, and Combi-Blocks) and used without further purification; all solvents were analytical grade. Thin layer chromatography (TLC) was performed using silica gel GF254, 0.25 mm thickness; visualization was accomplished with short wave UV light or KMnO4 staining solution, followed by heating. Melting points were measured on a Buchi M-560 melting point apparatus and are uncorrected. Hydrogen nuclear magnetic resonance spectra (1H NMR) were obtained at 400 and 500 MHz in CDCl3 solutions, at ambient temperature. Carbon-13 nuclear magnetic resonance spectra (13C NMR) were obtained at 100 and 125 MHz in CDCl3 solutions, at ambient temperature. Chemicals shifts (δ) are given in ppm, and the residual solvent signals were used as references for 1H and 13C NMR spectra (CDCl3: δH = 7.27 ppm, δC = 77.00 ppm). High resolution mass spectra were recorded on Thermo Scientific LTQ FT Ultra and Q Exactive Orbitrap spectrometers working with an electronspray ionization (ESI). General Procedure and Characterization of Products. (A) General Procedure for Epoxyacylation. Conjugated olefin (1 mmol, 1.0 equiv), aldehyde (2 mmol, 2.0 equiv), K2S2O8 (2.0 mmol, 2.0 equiv), and methylene blue (0.025 mmol, 0.025 equiv) were added to 7 mL of an aqueous solution of K2CO3 (0.5 M, 3.5 mmol). The resulting air-equilibrated suspension was capped with a rubber septum and irradiated at room temperature for 12 h using a household bulb (100 W) placed 8 cm from the flask. The stirring speed of the reaction mixture was kept at 1150 rpm to ensure diffusion of reaction components. After completion of the reaction, ethyl acetate (3 mL) was added for quenching. The aqueous layer was extracted with ethyl acetate (3 mL), and the combined organic layers were dried over anhydrous Na2SO4 and concentrated. The crude mixture was filtered through a plug of silica (approximately 5 cm) using a mixture of ethyl acetate/n-hexane (5:95) and followed by TLC to afford the desired pure product. (B) General Procedure for Hydroacylation. Nonconjugated olefin (1 mmol, 1.0 equiv), benzaldehyde (2 mmol, 2.0 equiv), K2S2O8 (1.0 mmol, 1.0 equiv), and methylene blue (0.005 mmol, 0.005 equiv) were added to 7 mL of an aqueous solution of K2CO3 (2.5 M, 17.5 mmol). The resulting air-equilibrated suspension is capped with a rubber septum and irradiated at room temperature for 12 h using a household bulb (100 W) placed 8 cm from the flask. The stirring speed of the reaction mixture was kept at 1150 rpm to ensure diffusion of reaction components. After completion of the reaction, ethyl acetate (3 mL) was added for quenching. The aqueous layer was extracted with ethyl acetate (3 mL), and the combined organic layers were dried over anhydrous Na2SO4 and concentrated. The crude mixture was filtered through a plug of silica (approximately 5 cm) using a mixture of ethyl acetate/n-hexane (3:97) and followed by TLC to afford the desired pure product. Phenyl(3-phenyloxiran-2-yl)methanone (3a). Prepared from styrene and benzaldehyde following the general procedure A to give the product as a colorless oil (92% yield, 206.3 mg). All data were consistent with those previously reported.5d 1H NMR (500 MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.89 Hz), 4.31 (d, 1H, J = 1.89 Hz), 7.37−7.45 (m, 5H),7.48−7.52 (m, 2H), 7.61−7.66 (m, 1H), 8.02 (dd, 2H, J = 8.18, 1.26 Hz). 13C NMR (125 MHz, Chloroformd): δ 59.3, 60.9, 125.7, 128.3, 128.7, 128.80, 128.85, 129.0, 133.9, 135.4, 193.1. (2-Chlorophenyl)(3-phenyloxiran-2-yl)methanone (3b). Prepared from styrene and 3-chlorobenzaldehyde following the general procedure A to give the product as a colorless oil (82% yield, 212.1 mg). All data were consistent with those previously reported.17 1H NMR (400 MHz, Chloroform-d): δ 4.11 (d, 1H, J = 1.96 Hz), 4.16 8337


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NMR (125 MHz, Chloroform-d): δ 14.1, 21.6, 22.7, 24.5, 29.31, 29.40, 29.48, 29.56, 31.9, 38.5, 128.2, 129.2, 134.6, 143.5, 200.3. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C18H30O 261.2218; Found 261.2225. 1-Phenyltridecan-1-one (5d). Prepared from 1-dodecene and benzaldehyde following the general procedure B to give the product as a colorless oil (82% yield, 225.0 mg). All data were consistent with those previously reported.25 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 6.85 Hz), 1.23−1.42 (m, 18H), 1.74 (quint, 2H, J = 7.34 Hz), 2.97 (t, 2H, J = 7.34 Hz), 7.47 (t, 2H, J = 7.34 Hz), 7.56 (t, 1H, J = 7.34 Hz), 7.96 (d, 2H, J = 7.35 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.4, 29.34, 29.38, 29.48, 29.51, 29.56, 29.59, 29.63, 29.66, 31.9, 38.6, 128.05, 128.53, 132.8, 137.1, 200.6. 1-(4-Chlorophenyl)tridecan-1-one (5e). Prepared from 1-dodecene and 4-chlorobenzaldehyde following the general procedure B to give the product as a white solid (75% yield, 231.7 mg, mp = 81−84 °C). All data were consistent with those previously reported.25 1H NMR (400 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 7.34 Hz), 1.23− 1.38 (m, 18H), 1.73 (quint, 2H, J = 7.34 Hz), 2.93 (t, 2H, J = 7.34 Hz), 7.43 (d, 2H, J = 8.80 Hz), 7.89 (d, 2H, J = 8.50 Hz). 13C NMR (100 MHz, Chloroform-d): δ 14.1, 22.7, 24.3, 29.34, 29.45, 29.48, 29.55, 29.60, 29.64, 31.9, 38.6, 128.8, 129.5, 135.4, 139.3, 199.3. 1-(4-Methoxyphenyl)tridecan-1-one (5f). Prepared from 1-dodecene and 4-methoxybenzaldehyde following the general procedure B to give the product as a colorless oil (84% yield, 255.8 mg). All data were consistent with those previously reported.25 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 7.34 Hz), 1.21−1.38 (m, 18H), 1.72 (quint, 2H, J = 7.21 Hz), 2.91 (t, 2H, J = 7.80 Hz), 3.88 (s, 3H), 6.93 (d, 2H, J = 8.75 Hz), 7.94 (d, 2H, J = 8.65 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.7, 29.32, 29.45, 29.50, 29.56, 29.59, 29.63, 29.66, 31.9, 38.3, 55.4, 113.6, 130.25, 130.31, 163.2, 199.2. 1-Phenylpentadecan-1-one (5g). Prepared from 1-tetradecene and benzaldehyde following the general procedure B to give the product as a colorless oil (71% yield, 214.8 mg). All data were consistent with those previously reported.26 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 6.85 Hz), 1.23−1.38 (m, 22H), 1.74 (quint, 2H, J = 7.00 Hz), 2.97 (t, 2H, J = 7.34 Hz), 7.46 (t, 2H, J = 7.83 Hz), 7.56 (t, 1H, J = 7.34 Hz), 7.96 (d, 2H, J = 7.34 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.4, 29.35, 29.45, 29.48, 29.51, 29.56, 29.63, 29.66, 31.9, 38.6, 128.05, 128.53, 132.8, 137.1, 200.6. 1-(4-Chlorophenyl)pentadecan-1-one (5h). Prepared from 1tetradecene and 4-chlorobenzaldehyde following the general procedure B to give the product as a colorless oil (67% yield, 225.7 mg). 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 7.55 Hz), 1.23−1.37 (m, 22H), 1.73 (quint, 2H, J = 6.92 Hz), 2.93 (t, 2H, J = 7.55 Hz), 7.43 (d, 2H, J = 8.80 Hz), 7.89 (d, 2H, J = 8.20 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.3, 29.34, 29.45, 29.48, 29.55, 29.59, 29.64, 31.9, 38.6, 128.8, 129.5, 135.4, 139.3, 199.3. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C21H35ClO 337.2298; Found 337.2271. 1-(4-Methoxyphenyl)pentadecan-1-one (5i). Prepared from 1tetradecene and 4-methoxybenzaldehyde following the general procedure B to give the product as a colorless oil (69% yield, 229.4 mg). 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 7.55 Hz), 1.23−1.39 (m, 22H), 1.73 (quint, 2H, J = 6.92 Hz), 2.93 (t, 2H, J = 7.00 Hz), 3.78 (s, 3H), 6.94 (d, 2H, J = 8.70 Hz), 7.94 (d, 2H, J = 8.70 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.3, 29.34, 29.45, 29.48, 29.54, 29.59, 29.64, 29.67, 31.9, 38.6, 55.8, 114.1, 129.5, 135.4, 165.0, 199.1. HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C22H38O2 333.2794; Found 333.2788.

A to give the product as a pale yellow oil (79% yield, 181.9 mg). All data were consistent with those previously reported.21 1H NMR (400 MHz, Chloroform-d): δ 1.22−1.35 (m, 6H), 1.45−1.65 (m, 4H), 2.58 (m, 1H), 3.60 (d, 1H, J = 1.47 Hz), 3.92 (d, 1H, J = 1.47 Hz), 7.28− 7.39 (m, 5H). 13C NMR (100 MHz, Chloroform-d): δ 25.3, 25.85, 25.69, 27.5, 28.4, 46.8, 58.4, 62.0, 125.7, 128.7, 128.9, 135.4, 207.9. Phenyl(3-(p-tolyl)oxiran-2-yl)methanone (3k). Prepared from 1methyl-4-vinylbenzene and benzaldehyde following the general procedure A to give the product as a pale yellow oil (90% yield, 214.4 mg). All data were consistent with those previously reported.6f 1 H NMR (400 MHz, Chloroform-d): δ 2.39 (s, 3H), 4.05 (d, 1H, J = 1.96 Hz), 4.30 (d, 1H, J = 1.96 Hz), 7.22 (d, 2H, J = 7.83 Hz), 7.27 (d, 2H, J = 7.83 Hz), 7.50 (t, 2H, J = 7.83 Hz), 7.63 (t, 1H, J = 7.34 Hz), 8.01 (d, 2H, J = 7.34 Hz). 13C NMR (100 MHz, Chloroform-d): δ 21.2, 59.4, 61.0, 125.7, 128.3, 128.8, 129.4, 132.4, 133.9, 135.5, 139.0, 193.2. (3-(4-Methoxyphenyl)oxiran-2-yl)(phenyl)methanone (3l). Prepared from 1-methoxy-4-vinylbenzene and benzaldehyde following the general procedure A to give the product as a pale yellow oil (75% yield, 190.7 mg). All data were consistent with those previously reported.6f 1H NMR (400 MHz, Chloroform-d): δ 3.82 (s, 3H), 4.01 (d, 1H, J = 1.90 Hz), 4.26 (d, 1H, J = 1.90 Hz), 6.95 (d, 2H, J = 8.75 Hz), 7.29 (d, 2H, J = 8.75 Hz), 7.49 (t, 2H, J = 7.34 Hz), 7.61 (t, 1H, J = 7.15 Hz), 8.02 (d, 2H, J = 7.34 Hz). 13C NMR (100 MHz, Chloroform-d): δ 55.7, 59.4, 61.0, 114.3, 127.07, 127.13, 128.29, 128.74, 133.9, 135.5, 160.3, 193.2. Phenyl(3-(pyridin-2-yl)oxiran-2-yl)methanone (3m). Prepared from 2-vinylpyridine and benzaldehyde following the general procedure A to give the product as a colorless oil (83% yield, 186.9 mg). All data were consistent with those previously reported.22 1H NMR (400 MHz, Chloroform-d): δ 4.23 (d, 1H, J = 1.80 Hz), 4.57 (d, 1H, J = 1.65 Hz), 7.31 (ddd, 1H, J = 7.50, 4.70, 1.25 Hz), 7.41 (d, 1H, J = 7.80 Hz), 7.48−7.54 (m, 2H), 7.58−7.62 (m, 1H), 7.75 (td, 1H, J = 7.65, 1.50 Hz), 8.00−8.07 (m, 2H), 8.60 (d, 1H, J = 4.60 Hz). 13 C NMR (100 MHz, Chloroform-d): δ 59.3, 121.2, 123.8, 128.4, 128.8, 134.0, 135.4, 137.0, 149.8, 154.5, 193.0. 3-(4-Chlorophenyl)oxiran-2-yl)(phenyl)methanone (3n). Prepared from 1-chloro-4-vinylbenzene and benzaldehyde following the general procedure A to give the product as a pale yellow oil (91% yield, 235.4 mg). All data were consistent with those previously reported.6f 1H NMR (400 MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.60 Hz), 4.24 (d, 1H, J = 1.65 Hz), 7.30 (d, 2H, J = 8.80 Hz), 7.38 (d, 2H, J = 8.80 Hz), 7.49 (t, 2H, J = 7.89 Hz), 7.63 (t, 1H, J = 7.35 Hz), 7.97 (d, 2H, J = 8.31 Hz). 13C NMR (100 MHz, Chloroform-d): δ 58.6, 60.8, 127.1, 128.02, 128.80, 128.93, 133.9, 134.1, 134.8, 135.2, 192.6. 1-Phenylundecan-1-one (5a). Prepared from 1-decene and benzaldehyde following the general procedure B to give the product as a pale yellow oil (89% yield, 219.3 mg). All data were consistent with those previously reported.23 1H NMR (500 MHz, Chloroformd): δ 0.89 (t, 3H, J = 6.92 Hz), 1.22−1.33 (m, 14H), 1.74 (quint, 2H, J = 6.92 Hz), 2.97 (t, 2H, J = 7.55 Hz), 7.47 (t, 2H, J = 8.17 Hz), 7.56 (t, 1H, J = 7.55 Hz), 7.96 (d, 2H, J = 6.92 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.4, 29.30, 29.37, 29.46, 29.50, 29.56, 31.9, 38.6, 128.04, 128.53, 132.8, 137.1, 200.6. 1-(4-Chlorophenyl)undecan-1-one (5b). Prepared from 1-decene and 4-chlorobenzaldehyde following the general procedure B to give the product as a pale yellow oil (80% yield, 224.7 mg). All data were consistent with those previously reported.24 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 6.29 Hz), 1.23−1.40 (m, 14H), 1.73 (quint, 2H, J = 7.55 Hz), 2.93 (t, 2H, J = 7.55 Hz), 7.43 (d, 2H, J = 8.17 Hz), 7.90 (d, 2H, J = 8.17 Hz). 13C NMR (125 MHz, Chloroform-d): δ 14.1, 22.7, 24.3, 29.29, 29.45, 29.48, 29.55, 31.9, 38.6, 128.8, 129.5, 135.4, 139.3, 199.3. 1-(p-Tolyl)undecan-1-one (5c). Prepared from 1-decene and 4methylbenzaldehyde following the general procedure B to give the product as a pale yellow oil (87% yield, 226.6 mg). 1H NMR (500 MHz, Chloroform-d): δ 0.89 (t, 3H, J = 6.92 Hz), 1.22−1.33 (m, 14H), 1.73 (quint, 2H, J = 7.55 Hz), 2.42 (s, 3H), 2.93 (t, 2H, J = 7.55 Hz), 7.25 (d, 2H, J = 8.17 Hz), 7.86 (d, 2H, J = 8.17 Hz). 13C

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b01026. 8338


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Additional experiments probing the mechanism, other mechanistic hypotheses, sunlight gram-scale experiment, 1 H and 13C NMR data (PDF)

AUTHOR INFORMATION

Corresponding Author

*Phone: +55 19 35218794. Fax: +55 19 35213023. E-mail: [email protected]. ORCID

Airton G. Salles, Jr.: 0000-0002-9423-2552 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Fundaçaõ de Amparo à Pesquisa do Estado de São Paulo (FAPESP, São Paulo, Brazil) and Faepex-UNICAMP for financial support (Grant FAPESP 2017/18400-6).

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REFERENCES

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Visible-Light-Driven Epoxyacylation and Hydroacylation of Olefins

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