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Visible light-driven epoxyacylation and hydroacylation of olefins using methylene blue/persulfate system in water Gabriela Freitas Pereira de Souza, Juliano A. Bonacin, and Airton Gonçalves Salles J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 06 Jul 2018 Downloaded from http://pubs.acs.org on July 6, 2018

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The Journal of Organic Chemistry

Visible light-driven epoxyacylation and hydroacylation of olefins using methylene blue/persulfate system in water Gabriela F. P. de Souza a, Juliano A. Bonacin b and Airton G. Salles, Jr *a a

Department of Organic Chemistry, Institute of Chemistry, University of Campinas, P.O. Box

6154, Campinas, São Paulo, 13084-862, Brazil. b

Department of Inorganic Chemistry, Institute of Chemistry, University of Campinas, P.O. Box

6154, Campinas, São Paulo, 13084-862, Brazil. Email: [email protected] KEYWORDS: photoredox catalysis, C−H functionalization, epoxyacylation, hydroacylation, methylene blue

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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 non-conjugated olefins to deliver ketones and epoxyketones from abundant and inexpensive chemical feedstocks.

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 visible light-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


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addition of acyl radicals to olefins converts abundant chemical feedstocks into ketones and α,βepoxy 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).


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Scheme 1. Previous Work and Our Approach for Epoxyacylation/Hydroacylation

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 photocatalysis, the development of methods employing alternatives to organic


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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 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. 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, 35% of the epoxyketone 3a was formed. Increasing the concentration of base and decreasing the oxidant loading to 1.0 equivalent led to inferior yield (Table 1, entry 2).


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Table 1. Optimization of the Visible Light-driven Epoxyacylation

entry

methylene blue (mol%)

base (mol L-1)

K2S2O8 (equiv)

solvent

yield

1

2.5

K2CO3 (1.0)

2.0

water

35%

2

2.5

K2CO3 (1.5)

1.0

water

26%

3

2.5

K2CO3 (0.5)

1.0

water

47%

4

2.5

K2CO3 (0.5)

2.0

water

92%

5

5.0

K2CO3 (0.5)

2.0

water

72%

6

2.5

NaOH (0.5)

2.0

water

25%

7

-

K2CO3 (0.5)

2.0

water

10%

8

2.5

-

2.0

water

traces

9

2.5

K2CO3 (0.5)

-

water

0%

10a

2.5

K2CO3 (0.5)

2.0

water

14%

11b

2.5

K2CO3 (0.5)

2.0

water

65%

12

2.5

K2CO3 (0.5)

2.0

acetonitrile

38%

General conditions: 7 ml of water, 1 (1 mmol), 2 (2 mmol), visible light (100 W household bulb), 25 oC, 12 h. Yield of isolated product . a No light. b N2 atmosphere.

To our delight, decreasing the concentration of base to 0.5 M and using 2 equivalents of potassium persulfate gave access to the targeted product in 92% yield with an excellent


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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 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 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.


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Scheme 2. Scope of the Visible Light-driven Epoxyacylation

3a, 92%

3b, 82%

3c, 88%

3d, 85%

3e, 89%

3f, 90%

3g, 84%

3i, 82%

3h, 87%

3l, 75%

3k, 90%

3j, 79%

3m, 83%

3n, 91%

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

Next, we extended our method to non-conjugated 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 agents11;


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hence, we decided to re-optimize the reaction conditions to provide a range of these products in acceptable yields. Table 2. Optimization of the Visible Light-driven Hydroacylation

entry

methylene blue (mol%)

base (mol L-1)

K2S2O8 (equiv)

solvent

yield

1

2.5

K2CO3 (0.5)

2.0

water

35%

2

2.5

K2CO3 (1.0)

2.0

water

47%

3

1.2

K2CO3 (1.0)

2.0

water

40%

4

1.2

K2CO3 (2.0)

2.0

water

55%

5

1.2

K2CO3 (2.0)

3.0

water

23%

6

1.2

K2CO3 (2.0)

1.0

water

61%

7

1.2

K2CO3 (2.5)

2.0

water

50%

8

0.5

K2CO3 (2.5)

1.0

water

89%

9

-

K2CO3 (2.5)

1.0

water

8%

10

0.5

-

1.0

water

traces

11

0.5

K2CO3 (2.5)

-

water

0%

12a

0.5

K2CO3 (2.5)

1.0

water

traces

13b

0.5

K2CO3 (2.5)

1.0

water

50%

14

0.5

K2CO3 (2.5)

1.0

acetonitrile

0%

General conditions: 7 ml of water, 4 (1 mmol), 2 (2 mmol), visible light (100 W household bulb), 25 oC, 12 h. Yield of isolated product . a No light. b N2 atmosphere.


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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 equivalent 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 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 electronwithdrawing substituents on the benzaldehyde aryl moiety together with different size long-chain 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, and as such we concluded that these substrates are not suitable for this transformation. Submitting styrenes (Styrene, 1-Chloro-4-vinylbenzene and 1-Methoxy-4-vinylbenzene) to the optimized hydroacylation conditions led to the corresponding epoxyketones in traces and recovery of starting materials unreacted. These results show that only non-conjugated, long-chain olefins are likely to participate in the hydroacylation reaction.


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Scheme 3. Scope of the Visible Light-driven Hydroacylation

5a, 89%

5b, 80%

5c, 87%

O Me 5 5d, 82%

5e, 75%

5f, 84%

5g, 71%

5h, 67%

5i, 69%

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

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.


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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 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-


12

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opening reaction along with several unidentifiable by-products were formed, thus excluding this hypothesis.


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Scheme 5. Studies on the mechanism

Next, we hypothesized that hydroperoxyl radical generated in the reaction medium would combine with (D) (which comes from acyl radical addition to the olefin) leading to the


14

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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 different substituents (Scheme 6, item 2, see the Supporting Information for details). The results showed that this transformation is more favourable 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


15


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Scheme 6. More studies on the mechanism

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 single-electron transfer (SET) with the hydroperoxide anion (E1/2 = ˗0.88 V vs SHE)14 generated from persulfate alkaline hydrolysis to afford


16

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hydroperoxyl radical and methylene blue neutral radical (Scheme 7, step I, see the Supporting Information for control experiments and references 12 and 13(a)). 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).


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Scheme 7. Proposed reaction mechanism

CONCLUSION In summary, we have developed a visible light-driven hydroacylation and epoxyacylation of non-conjugated and conjugated olefins with a variety of aldehydes using methylene blue as an organophotoredox catalyst and potassium persulfate as an 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-scale under sunlight with no detrimental effect on yield. We


18

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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.

EXPERIMENTAL SECTION

General Information

All reagents were purchased from commercial suppliers (Sigma-Aldrich, Oakwood and CombiBlocks) 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 Buchi M-560 melting point apparatus and are uncorrected. Hydrogen nuclear magnetic resonance spectra (1H NMR) were obtained at 400 MHz and 500 MHz in CDCl3 solutions, at ambient temperature. Carbon-13 nuclear magnetic resonance spectra (13C NMR) were obtained at 100 MHZ 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

13

C 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).


19


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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), 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 Non-conjugated 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), 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.


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Phenyl(3-phenyloxiran-2-yl)methanone (3a). Prepared from styrene and benzaldehyde following the general procedure A to give the product as a colourless oil (92% yield, 206.3 mg). All data was consistent with that previously reported.5d 1H NMR (500MHz, 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).

13

C NMR (125MHz, Chloroform-d): 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 3chlorobenzaldehyde following the general procedure A to give the product as a colourless oil (82% yield, 212.1 mg). All data was consistent with that previously reported.17 1H NMR (400MHz, Chloroform-d): δ 4.11 (d, 1H, J = 1.96 Hz), 4.16 (d, 1H, J = 1.96 Hz), 7.35–7.44 (m, 8H), 7.64 (dd, 1H, J = 7.83, 1.47 Hz). 13C NMR (100MHz, 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 3chlorobenzaldehyde following the general procedure A to give the product as a white solid (88% yield, 227.7 mg, m.p. = 85−87 oC). All data was consistent with that previously reported.17 1H NMR (500MHz, 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).

13

C NMR

(125MHz, 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 4chlorobenzaldehyde following the general procedure A to give the product as a white solid (85% yield, 219.9 mg, m.p. = 123−125 oC). All data was consistent with that previously reported.5d 1H NMR (400MHz, Chloroform-d): δ 4.09 (d, 1H, J = 1.00 Hz), 4.24 (d, 1H, J = 1.00 Hz), 7.36–


21


Page 22 of 35

7.43 (m, 5H), 7.47 (d, 2H, J = 8.30 Hz), 7.97 (d, 2H, J = 8.30 Hz).

13

C NMR (100MHz,

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 was consistent with that previously reported.18 1H NMR (500MHz, 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).

13

C NMR (125MHz,

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 4methoxybenzaldehyde following the general procedure A to give the product as a white solid (90% yield, 228.9 mg, m.p. = 77−79 oC). All data was consistent with that previously reported.5d 1

H NMR (400MHz, 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).

13

C NMR

(100MHz, 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 1naphthaldehyde following the general procedure A to give the product as a white solid (84% yield, 230.4 mg, m.p. = 109−111 oC). All data was consistent with that previously reported.19 1H NMR (500MHz, 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).

13

C NMR (125MHz,

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.


22

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(4-fluorophenyl)(3-phenyloxiran-2-yl)methanone (3h). Prepared from styrene and 4fluorobenzaldehyde following the general procedure A to give the product as a white solid (87% yield, 210.8 mg, m.p. = 82−84 oC). All data was consistent with that previously reported.20 1H NMR (400MHz, 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).

13

C NMR (100MHz, 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 (500MHz, 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).

13

C NMR (125MHz,

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 A to give the product as a pale yellow oil (79% yield, 181.9 mg). All data was consistent with that previously reported.21 1H NMR (400MHz, 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 (100MHz, 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 1-methyl-4-vinylbenzene and benzaldehyde following the general procedure A to give the product as pale yellow oil (90% yield, 214.4 mg). All data was consistent with that previously reported.6f 1H NMR (400MHz,


23


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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).

13

C NMR (100MHz, 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-4vinylbenzene and benzaldehyde following the general procedure A to give the product as pale yellow oil (75% yield, 190.7 mg). All data was consistent with that previously reported.6f 1H NMR (400MHz, 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).

13

C NMR (100MHz, 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 colourless oil (83% yield, 186.9 mg). All data was consistent with that previously reported.22 1H NMR (400MHz, 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 (100MHz,

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 pale yellow oil (91% yield, 235.4 mg). All data was consistent with that previously reported.6f 1H NMR (400MHz, 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),


24

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7.97 (d, 2H, J = 8.31 Hz).

13

C NMR (100MHz, 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 was consistent with that previously reported.23 1H NMR (500MHz, Chloroform-d): 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).

13

C NMR (125MHz,

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 was consistent with that previously reported.24 1H NMR (500MHz, 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 (125MHz, Chloroformd): 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 4-methylbenzaldehyde following the general procedure B to give the product as a pale yellow oil (87% yield, 226.6 mg). 1H NMR (500MHz, 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).

13

C NMR (125MHz, 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.


25


Page 26 of 35

1-phenyltridecan-1-one (5d). Prepared from 1-dodecene and benzaldehyde following the general procedure B to give the product as colourless oil (82% yield, 225.0 mg). All data was consistent with that previously reported.25 1H NMR (500MHz, 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).

13

C NMR (125MHz,

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, m.p. = 81−84 oC). All data was consistent with that previously reported.25 1H NMR (400MHz, 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).

13

C NMR

(100MHz, 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 colourless oil (84% yield, 255.8 mg). All data was consistent with that previously reported.25 1H NMR (500MHz, 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).

13

C NMR (125MHz, 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 colourless oil (71% yield, 214.8 mg). All data was


26

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consistent with that previously reported.26 1H NMR (500MHz, 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).

13

C NMR (125MHz,

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

1-tetradecene

and

4-

chlorobenzaldehyde following the general procedure B to give the product as colourless oil (67% yield, 225.7 mg).

1

H NMR (500MHz, 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).

13

C NMR (125MHz, 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

1-tetradecene

and

4-

methoxybenzaldehyde following the general procedure B to give the product as colourless oil (69% yield, 229.4 mg). 1H NMR (500MHz, 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).

13

C NMR (125MHz, 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.

ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website at DOI:


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Additional experiments probing the mechanism, other mechanistic hypotheses, sunlight gramscale experiment, 1H 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 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS We thank Fundação 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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Wang, L. X.; Xu, X. F.; Zhou, Q. L. Nickel-Catalyzed Hydroacylation of Styrenes with Simple Aldehydes: Reaction Development and Mechanistic Insights. J. Am. Chem. Soc. 2016, 138, 2957˗2960. (d) Ke, Q.; Zhang, B.; Hu, B.; Jin, Y.; Lu, G. A Transition-Metal-Free, One-pot Procedure for the Synthesis of α,β-epoxy ketones by Oxidative Coupling of Alkenes and Aldehydes via Base Catalysis. Chem. Commun. 2015, 51, 1012˗1015. (6) (a) Papadopoulos, G. N.; Voutyritsa, E.; Kaplaneris, N.; Kokotos, C. G. Green PhotoOrganocatalytic C−H Activation of Aldehydes: Selective Hydroacylation of Electron‐Deficient Alkenes. Chem. Eur. J. 2018, 24, 1726˗1731. (b) Bonassi, F.; Ravelli, D.; Protti, S.; Fagnoni, M. Decatungstate Photocatalyzed Acylations and Alkylations in Flow via Hydrogen Atom Transfer. Adv. Synth. Catal. 2015, 357, 3687˗3695. (c) Moteki, S. A.; Usui, A.; Selvakumar, S.; Zhang, T.; Maruoka, K. Metal-Free C−H Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible-Light Photolysis: Successful Trapping with Electron-Deficient Olefins. Angew. Chem. Int. Ed. 2014, 53, 11060˗11064. (d) Ravelli, D.; Zema, M.; Mella, M.; Fagnoni, M.; Albini, A. Benzoyl Radicals From (hetero)aromatic Aldehydes. Decatungstate Photocatalyzed Synthesis of Substituted Aromatic Ketones Org. Biomol. Chem. 2010, 8, 4158˗4164. (e) Esposti, S.; Dondi, D.; Fagnoni, M.; Albini, A. Acylation of Electrophilic Olefins through Decatungstate-Photocatalyzed Activation of Aldehydes. Angew. Chem. Int. Ed. 2007, 46, 2531˗2534. (f) J. Li, J.; Wang, D. Z. Visible-Light-Promoted Photoredox Syntheses of α,βEpoxy Ketones from Styrenes and Benzaldehydes under Alkaline Conditions. Org. Lett. 2015, 17, 5260˗5263. (g) Keshari, T.; Yadav, V. K.; Srivastava, V. P.; Yadav, L. D. S. Visible Light Organophotoredox Catalysis: A General Approach to β-Keto Sulfoxidation of Alkenes. Green Chem. 2014, 16, 3986˗3989.


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