Organoselenium-Catalyzed Oxidative C C Bond Cleavage: A

Aug 16, 2017 - A relatively green oxidative C═C bond cleavage of alkenes was achieved by organoselenium-catalyzed alkene oxidation reaction in ethan...
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Organoselenium-Catalyzed Oxidative CC Bond Cleavage: A Relatively Green Oxidation of Alkenes into Carbonyl Compounds with Hydrogen Peroxide Tingting Wang,† Xiaobi Jing,† Chao Chen, and Lei Yu* School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, China S Supporting Information *

ABSTRACT: A relatively green oxidative CC bond cleavage of alkenes was achieved by organoselenium-catalyzed alkene oxidation reaction in ethanol with hydrogen peroxide, affording carbonyl compounds under relatively mild conditions. It is a new reaction style for the organoselenium-catalyzed oxidation of alkenes and largely contributes to the growing field of organoselenium catalysis.

1. INTRODUCTION Organoselenium catalysis is a unique topic just unfolding in recent years.1−4 It has attracted much attention in both academia and industry owning to its green features3,4 since, first, selenium is a metabolizable element that does not accumulate in organisms and is very eco-friendly.1a,c,3c,5 Second, organoselenium-catalyzed reactions are usually transition-metalfree, which can avoid the heavy metal contaminant in the products. Moreover, organic selenium compounds are much less toxic than inorganic selenium compounds. Among the frequently used organoselenium catalysts, diselenides exhibit only moderate toxicity.6 In addition, organoselenium catalysts are very stable and can be recycled and reused for many times without deactivation.4a−e Regarding the organoseleniumcatalyzed oxidation reactions, H2O2 is usually employed as the oxidant, which is clean and will not generate other waste than the water. During the last three years, we have achieved a series of organoselenium-catalyzed green transformations, such as the dihydroxylation of cyclohexenes,4b,d,f Baeyer−Villiger oxidation of ketones,4c dehydration of aldoximes,4e and deoximation.4a On the other hand, oxidation of alkenes is an important subject because of the broad application scope. It has also attracted much attention from organic chemists for the changeful reaction selectivities. Generally, there are three paths for alkene oxidation (Scheme 1): the allylic C−H oxidations lead to α,β-unsaturated ketones, aldehydes or alcohols,7 or heterocycles for certain well-designed substrates (Scheme 1, path A);8 the oxidations of CC bond produce epoxides or 1,2-diols (Scheme 1, path B);9 the oxidative scissions of alkenes are very important transformations for the synthesis of carbonyl compounds, deprotection of the functional groups, and degradation of large molecules, such as the derivatives from biomass,10 but many of them require transition metal catalysts, strong chemical oxidants or nitro-contained solvents that generate large amount of wastes and are unfriendly to environments (Scheme 1, path C). In the field © 2017 American Chemical Society

Scheme 1. Three Paths for Alkene Oxidation

of organoselenium catalysis, the former two conversions have already been achieved by us4b,d,f and other groups,3c,d,11 while the oxidative alkene scission still remains a tremendous challenge that has not been conquered yet, probably due to the high CC bond energy and the relatively complex reaction paths. Recently, after a series of catalyst screenings and condition optimizations, we successfully cut off the double bond of alkenes by using H2O2 as oxidant and diselenides as catalyst to produce carbonyls. The reaction provided a relatively green synthetic tool and largely expanded the scope of organoselenium catalysis. Herein, we report our findings.

2. RESULTS AND DISCUSSION The oxidation reaction of ethene-1,1-diyldibenzene (1a) was initially chosen as the template for catalyst screenings (Table 1). Heating alkene 1a with H2O2 in the presence of (PhSe)2 catalyst in MeCN at 80 °C for 48 h, the desired product benzophenone (3a) was obtained in 48% yield (Table 1, entry Received: May 21, 2017 Published: August 16, 2017 9342

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

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The Journal of Organic Chemistry Table 1. Catalyst Screeningsa

Table 2. Condition Optimizationsa,b

entry

R

t (h)b

3a (%)c

entry

cat (%)

2:1a

conditionsc

3a (%)d

1 2 3 4 5 6 7 8 9 10 11

Ph 4-MeC6H4 4-MeOC6H4 4-Me2NC6H4 3,5-(CF3)2C6H3 4-FC6H4 3-FC6H4 2-FC6H4 PhCH2 n-C4H9 c-C6H11

48 48 48 48 15 48 48 48 15 14 12

48d 42d 39d 23d 48 51d 45d 30d 57 55 66

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

10 5 3 1 0.5 0 5 5 5 5 5 5 5 5 5 5 5 5 5 5

5 5 5 5 5 5 6 4 2 1 5 5 5 5 5 5 5 5 5 5

MeCN, 80 °C, 8 h MeCN, 80 oC, 12 h MeCN, 80 °C, 12 h MeCN, 80 °C, 36 h MeCN, 80 °C, 48 h MeCN, 80 °C, 48 h MeCN, 80 °C, 12 h MeCN, 80 °C, 36 h MeCN, 80 °C, 48 h MeCN, 80 °C, 48 h MeCN, 80 oC, 48 h H2O, 80 °C, 48 h acetone, 80 °C, 48 h EtOH, 80 oC, 48 h i PrOH, 80 °C, 48 h t BuOH, 80 °C, 48 h EtOH, 70 °C, 48 h EtOH, 60 °C, 48 h EtOH, 100 °C, 36 h EtOH, 100 °C, 48 h

57 66 60 56e 38e 8e 67 64e 36e 23e 70 48e 20e 74e 59e 51e 50e 30e 72 55

a

Reaction conditions: 0.5 mmol 1a, 2.5 mmol H2O2 (30 w/w %), and 2 mL of MeCN were employed. bReactions were monitorred by TLC. c Isolated yields based on 1a. dReaction not completed.

1). A series of diselenides were then tested and it was found that the product yield decreased with the increase of the electron density of the diselenide catalysts (Table 1, entries 2− 4 vs 1). [3,5-(CF3)2C6H3Se]2, the favorite catalyst for alkene epoxidation and dihydroxylation that has been screened by us and others previously,3d,4d was unfortunately unfavorable for the oxidative CC cleavage and led to 3a in only 48% yield (Table 1, entry 5). Using electron-deficient (4-FC6H4Se)2, the product yield could be slightly enhanced to 51% (Table 1, entry 6), but the diselenide catalysts with fluorine at meta- and orthopositions were obviously less reactive (Table 1, entries 7−8). Interestingly, dialkyl diselenides, such as (PhCH2Se)2, (nC4H9Se)2, and (c-C6H11Se)2 (1,2-dicyclohexyldiselane), which were rarely employed in organoselenium catalysis, were preferable catalysts and the reactions finished within 12−15 h to produce 3a in 55−66% yields (Table 1, entries 9−11). The reaction conditions were then further optimized. Elevated catalyst amount accelerated the procedure, but depressed the desired product yield (Table 2, entries 1 vs 2), while the reduced catalyst dosages retarded the reactions (Table 2, entries 3−5 vs 2). A blank reaction without organoselenium catalyst was also tested, but afforded the product 3a in only 8% yield, while most of the starting materials were not converted (Table 2, entry 6). The reaction was hardly improved with enhanced H2O2 dosage (Table 2, entry 7). It was found that excess H2O2 was crucial for the full conversion of 1a (Table 2, entries 2 vs 8−10). Extension of the reaction time to 48 h could further improve the product yield (Table 2, entries 11 vs 2). Water or acetone as solvent resulted in very poor 3a yield (Table 2, entries 12−13). Reactions in alcohol solvent were also tested and it was found that although the reaction speed was reduced in ethanol, its product yield was increased to 74% (Table 2, entries 14−16). The reactions were decelerated at 60−70 °C (Table 2, entries 17−18). Enhanced reaction temperature at 100 °C led to a full conversion of 1a within 36 h (Table 2, entry 19), and the product yield decreased with extended reaction time, possibly due to the generation of a series of overoxidation byproducts such as benzoic acid, phenol, and benzoyl peroxide, etc., as detected by GC-MS analysis (Table 2, entry 20).12

a

Reaction conditions: 0.5 mmol 1a and 2 mL of solvent were employed. bCat (%) = molar ratio of (c-C6H11Se)2 vs 1a; 2:1a = molar ratio of H2O2 vs 1a. cReactions were monitored by TLC. dIsolated yields of 3a based on 1a. eReaction not completed.

We then tried to expand the application scopes of the reaction to other gem-disubstituted ethenes (Table 3). Besides 1a, the oxidative CC bond cleavage of bulky alkene 1b could also occur, but both high temperature and extended reaction time were required for the transformation (Table 3, entries 2 vs 1). Catalyzed by (n-C4H9Se)2, the electron-deficient substrate 1c produced 3c in 72% yield (Table 3, entry 3). Similarly, the oxidation of 1d provided 3d in 65% yield, whereas (PhCH2Se)2 as catalyst and high reaction temperature at 120 °C were required (Table 3, entry 4). Alkene 1e with strong electron donation groups led to the product 3e in 50% yield and the generation of the complex byproducts was also observed (Table 3, entry 5). Oxidation of 1f generated acetophenone (3f) in 70% GC yield, but due to the product volatility, the isolated yield decreased to 51% after purification (Table 3, entry 6). (PhCH2Se)2-catalyzed oxidation reaction of 1g at 120 °C led to 3g in 62% yield (Table 3, entry 7). It was very interesting that the strained cyclopropyl ring showed some degree of stability under the highly oxidative and acidic conditions and the product cyclopropyl(phenyl)methanone (3h) was smoothly synthesized in moderate yield from 1h (Table 3, entry 8). Reactions of the bulky, electron-deficient and electron-enriched methyl alkenes 1i−k produced the corresponding ketones 3i−k in moderate yields, respectively (Table 3, entries 9−11). The protocol was also effective for exocyclic CC bond, and 2,3dihydro-1H-inden-1-one (3l) could be prepared through the oxidative demethylene reaction of alkene 1l (Table 3, entry 12). Experiments with aliphatic alkenes were also conducted: oxidation of methylenecyclohexane 1m afforded cyclohexanone (3m) in 73% GC yield, while oxepan-2-one, the deep oxidation byproduct,3e was also generated in 8% GC yield (Table 3, entry 9343

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

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The Journal of Organic Chemistry Table 3. Oxidation of the gem-Disubstituted Ethenesa

a

Reaction conditions: 0.5 mmol 1, 2.5 mmol H2O2 and 2 mL of EtOH were employed. bIsolated yields of 3 based on 1 outside the brackets and GC yields of 3 inside the brackets (with biphenyl as internal standard). cReaction performed in a sealed tube. dOxepan-2-one was also generated in 8% GC yield. eEthyl acetate was also generated in 56% GC yield.

product (in 56% GC yield) due to the high activity of 3n in Baeyer−Villiger oxidations3e,4c under the strong oxidation conditions (Table 3, entry 14).

13). In the reaction of chained aliphatic alkene 2-methylbutene (1n), besides the desired product butan-2-one (3n), the overoxidized product ethyl acetate was even generated as the major 9344

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

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The Journal of Organic Chemistry

Moreover, the oxidative CC bond cleavage reactions of (E)-1,2-diphenylethene (1ac) and (E)-prop-1-en-1-ylbenzene (1ad) led to the desired product benzaldehyde (3n) in 21− 22% yield, while the deep oxidation products benzoic acid (4) and its ester 5 were also obtained in 21−26% yields (eq 1). Like

Reactions of the 1,1,2-trisubstituted and tetrasubstituted ethenes were also tested (Table 4). Oxidation of 1,1Table 4. Oxidation of the 1,1,2-Trisubstituted and Tetrasubstituted Ethenesa

entry

R1, R2, R3, R4 (1)

1

Ph, Ph, Me, H (1o)

2

Ph, Ph, n-C3H7, H (1p)

3

Ph, Ph, Ph, H (1q)

4

8

4-ClC6H4, 4-ClC6H4, Me, H (1r) 4-ClC6H4, 4-ClC6H4, Ph, H (1s) 4-MeOC6H4, 4-MeOC6H4, Me, H (1t) 4-MeOC6H4, 4-MeOC6H4, Ph, H (1u) Me, Ph, Me, H (1v)

9

Me, Ph, Ph, H (1w)

10

1-C10H7, Ph, Me, H (1x)

11

1-C10H7, Ph, Ph, H (1y)

12

Ph, Ph, MeO, H (1z)

13

Ph, Ph, CO2Et, H (1aa)

14

Ph, Ph, Ph, Ph (1ab)

5 6 7

(RSe)2 conditions (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 80 °C (PhCH2Se)2, 120 °C (PhCH2Se)2, 120 °C (c-C6H11Se)2, 100 °C (c-C6H11Se)2, 100 °C (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 120 °C (c-C6H11Se)2, 120 °C (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 80 °C (c-C6H11Se)2, 120 °C

yield (%) (3)b 52 (3a) 50 (3a) 49 (3a) 62 (3d) 53 (3d) 57 (3e)

ethyl 3,3-diphenyl acrylate (1aa), the electron deficient alkene ethyl cinnamate (1ae) was stable under the reaction conditions and no reaction was detected (eq 1). Because of the low steric hindrance in substrate, the oxidation of styrene (1af) led to the addition product 2-ethoxy-2-phenylethan-1-ol (6) in 42% yield, and ethyl 2-phenylacetate (7) was also generated as the byproduct (eq 2). Cyclic alkenes as substrates were also tested:

54 (3e) 46 (65) (3f) 44 (62) (3f) 56 (3b)c 50 (3b)c 72 (3a) NRc,d trace (3a)c,e

a

Reaction conditions: 0.5 mmol 1, 2.5 mmol H2O2, and 2 mL of EtOH were employed. bIsolated yields of 3 based on 1 outside the brackets and GC yields of 3 inside the brackets (with biphenyl as internal standard). cReaction time was extended to 96 h. dNo reaction detected. eGC yield of 3a < 3%.

instead of CC cleavage, the reactions of cyclohexene (1ag) and 1-phenyl cyclohexene (1ah) led to the adducts transcyclohexane-1,2-diol (8a) and cis-1-phenylcyclohexane-1,2-diol (8b) respectively (eq 3). Introducing a phenyl obviously enhanced the activity of 1ah, and a series of unidentified complexes were also observed in TLC and GC-MS.

diphenylpropene (1o) afforded 3a in 52% yield (Table 4, entry 1). Replacing methyl with n-propyl or phenyl, the yields of 3a were slightly decreased (Table 4, entries 2−3). With (PhCH2Se)2 as catalyst, the oxidation reactions of electrondeficient trisubstituted ethenes 1r and 1s provided 3d in 53− 62% yields (Table 4, entries 4−5). Compared with the reaction of 1e, oxidations of electron-enriched trisubstituted ethenes 1t and 1u even produced 3e in slightly enhanced yields (Table 4, entries 6−7 vs Table 3, entry 5). Acetophenone 3f could be smoothly synthesized through the oxidation of trisubstituted ethenes 1v and 1w as well (Table 4, entries 8−9). Though bearing a bulky naphthalene group, both (E)-1-(1-phenylprop1-en-1-yl)naphthalene (1x) and (E)-1-(1,2-diphenylvinyl)naphthalene (1y) as substrates could lead to the desired product 3b in moderate yield at elevated temperature and with extended reaction time (Table 4, entries 10−11). The electronenriched trisubstituted ethene 1z as substrate led to elevated 3a yield over the reaction of 1o (Table 4, entries 12 vs 1), while the reaction of electron-deficient trisubstituted ethene 1aa was difficult to occur (Table 4, entry 13). Tetrasubstituted ethene, such as 1ab, was inactive for the reaction (Table 4, entry 14).

The mechanisms of this interesting reaction were our next concern. Because homo cleavage of Se−Se bond could happen to generate selenium free radicals under heating or visible light irradiation conditions,13 these organoselenium-catalyzed reactions might proceed through free radical reaction routes. Control experiments were performed to prove or exclude the possible mechanism: the addition of AIBN as free radical initiator promoted the reaction and the 3a yield was elevated to 82% (Table 5, entry 1 vs Table 3, entry 1); the reaction was restrained when free radical scavenger 2,2,6,6-tetramethyl-1piperidinyloxy (TEMPO) was added (Table 5, entry 2 vs Table 9345

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

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The Journal of Organic Chemistry Table 5. Control Experimentsa

entry

additives

3a (%)b

1 2 3 4

AIBN (5 mol %) TEMPO (100 mol %) − (in dark) TEMPO (100 mol %, in dark)

82 32c 68c 29c

dihydroxylation of the alkenes. Moreover, detection of the epoxide 10a and the over-oxidation byproduct 11a or 12a by GC-MS analysis further confirmed the existence of the intermediate step of the reaction (Scheme 2).12 On the basis of references 3 and 4, as well as the above experimental phenomenon, a plausible mechanism was supposed (Scheme 3). Organoselenium-catalyzed epoxidation of alkene 1 occurred initially to produce the epoxide 10 through free radical (as indicated by the results in Table 5)14 or electrophilic3d mechanisms. Hydration of 10 led to the diol 9,3c,4d,f which was then oxidized into the degraded carbonyl products through two catalysis cycles. In cycle A, the catalyst (RSe)2 was oxidized by H2O2 to furnish the active species RSe(O)OOH,4c,d which then dehydrated with 9 at the R3 other than R1, R2 site hydroxyl for the lower steric hindrance reason to produce 13.4e Rearrangement in 13 led to the intermediate 14 and RSe(O)OH, which could be oxidized by H2O2 to regenerate RSe(O)OOH.4c,d In cycle B, the nucleophilic addition of RSe(O)OOH with the generated 14 led to the organoselenium peroxide 15,4a in which the rearrangement produced the intermediate 16 and RSe(O)OH. Further hydration of 16 generated the final product 315 and carboxylic acids, which reacted with EtOH solvent and was observed in TLC as the byproduct ethyl benzoate 5 in the case of the reaction of 1q (Table 4, entry 3). It was difficult to generate the key intermediate 14 from tetrasubstituted ethenes. Thus, tetrasubstituted alkene 1ab was inactive for the reaction (Table 4, entry 10). Moreover, heating 2-hydroxy-1,2-diphenylethan-1-one (14a, intermediate for the reaction of 1ac in eq 1) with H2O2 in the presence of (cC6H11Se)2 catalyst afforded the desired product 4 in 72% yield (eq 6), further supporting that 14 might be the inevitable intermediate in the alkene oxidation reaction.

a

Reactions were performed under standard conditions described in Table 3, entry 1. bIsolated yields of 3a based on 1a. cReaction not completed.

3, entry 1). As the homocleavage of Se−Se bond to generate free radicals could be driven by visible light,13b the free radical procedures in this reaction were likely initiated by background visible light irradiation. A parallel experiment in dark was conducted and the yield of 3a was decreased by 6% (Table 5, entry 3 vs Table 3, entry 1). Addition of TEMPO into the reaction further reduced the 3a yield to 29% (Table 5, entry 4). Experimental results of these partially inhibited reactions indicated that the free radical procedures might be incorporated, but were not the only course in mechanisms, and both the thermal-initiated and visible-light-driven free radical generations were involved in the reaction. Experimental results in Table 2, entries 2 and 11 revealed more important clues for mechanism study: although the starting materials 1a disappeared in TLC after 12 h (Table 2, entry 2), the product yield could be further enhanced by extending the reaction time (Table 2, entry 11). The phenomena indicated that the reaction proceeded through two steps: the substrates were initially converted into certain reaction intermediates, and the prolonged reaction time facilitated the transformation of the intermediates into final products. According to the literature,3c,4d,f it was suggested that in the procedures dihydroxylation occurred first to produce the intermediate diols 9 (eq 4), which were then oxidized into degraded ketones.

In the dihydroxylation of alkene, electron-deficient diselenides, such as [3,5-(CF3)2C6H3Se]2, etc., were favorable catalysts,3d,4d while in the Baeyer−Villiger oxidation of ketones, electron-enriched diselenides were preferable.4c Thus, the conflict of the requirements on catalyst at different steps resulted in the difficulties in condition optimizations by adjusting electron density of the catalysts (Table 1, entries 1−8). As indicated by our previous investigations, the dialkyl diselenides were good catalysts for Baeyer−Villiger oxidations,4c which were involved as the key step of the oxidative CC bond cleavage (cycle B), and should be better catalysts for this transformation, but the complex reaction mechanisms that underwent dihydroxylation (eq 4) and alcohol oxidation (cycle A) resulted in the nongeneral applicability of the catalyst (Tables 3 and 4).

To support the above hypothesis, a reaction of 1,1diphenylethane-1,2-diol 9a with H2O2 was performed under standard conditions and the product 3a could be obtained in 64% yield as expected (eq 5). The oxidation of diol 9a was

3. CONCLUSION In conclusion, we have achieved the organoselenium-catalyzed oxidative scission of alkenes into carbonyls. The reactions were performed in ethanol with H2O2 as oxidant and were relatively green transformations. Although undergoing multiple steps including the alkene dihydroxylation, the alcohol oxidation, and the Baeyer−Villiger oxidation, the protocol still worked

hardly restrained by adding TEMPO (eq 5), indicating that the free radical reactions in the alkene oxidation processes only occurred in the starting steps, e.g. the epoxidation or 9346

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

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The Journal of Organic Chemistry Scheme 2. Reaction Intermediate Capture by GC-MS

Scheme 3. Possible Mechanisms

the related products. The GC yields were calculated according to the internal standard curves using biphenyl as the internal standard. 4.3. Characterization of the Products. Benzophenone 3a. 67.4 mg, 74%. Solid, mp 47.9−48.6 °C (lit. 48.5 °C). IR (KBr): 3055, 1660, 1590, 1445, 1276, 1158, 1076, 929, 702 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.79 (d, J = 7.2 Hz, 4H), 7.56 (t, J = 7.8 Hz, 2H), 7.46 (t, J = 7.8 Hz, 4H). 13C NMR (150 MHz, CDCl3): δ 196.8, 137.6, 132.5, 130.1, 128.3. Known compound.17a Naphthalen-1-yl(phenyl)methanone 3b. 60.3 mg, 52%. Solid, mp 75.1−76.0 °C (lit. 74.5−75.5 °C). IR (KBr): 3062, 1654, 1579, 1446, 1288, 1164, 1015, 791 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 8.09 (d, J = 8.4 Hz, 1H), 7.96 (d, J = 8.4 Hz, 1H), 7.88 (d, J = 7.8 Hz, 1H), 7.84 (d, J = 7.8 Hz, 2H), 7.56−7.54 (m, 2H), 7.50−7.45 (m, 3H), 7.41 (t, J = 7.8 Hz, 2H). 13C NMR (150 MHz, CDCl3): δ 198.1, 138.36, 136.39, 133.8, 133.3, 131.4, 131.0, 130.5, 128.53, 128.50, 127.9, 127.3, 126.5, 125.8, 124.4. MS (EI, 70 eV) m/z(%): 233 (6) [M+ + 1], 232 (34) [M+], 127 (100), 105 (43). Known compound.17b (4-Chlorophenyl)(phenyl)methanone 3c. 77.4 mg, 72%. Solid, mp 77.8−78.4 °C (lit. 77−78 °C). 1H NMR (600 MHz, CDCl3, TMS): δ 7.77−7.74 (m, 4H), 7.59 (t, J = 7.2 Hz, 1H), 7.49−7.44 (m, 4H). 13C NMR (150 MHz, CDCl3): δ 195.5, 138.9, 137.2, 135.9, 132.7, 131.5, 130.0, 128.7, 128.4. MS (EI, 70 eV) m/z (%): 217 (6) [M+ + 1], 216 (42) [M+], 105 (100), 181 (14). Known compound.17b Bis(4-chlorophenyl)methanone 3d. 81.6 mg, 65%. Solid, mp 147.2−147.9 °C (lit. 146−147 °C). IR (KBr): 1651, 1580, 1478, 1280, 1156, 1086, 842 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.72 (d, J = 7.2 Hz, 4H), 7.47−7.45 (m, 4H). 13C NMR (150 MHz, CDCl3): δ 194.2, 139.2, 135.5, 131.4, 128.8. MS (EI, 70 eV) m/z (%): 250 (9) [M+], 139 (100), 215 (6). Known compound.17c Bis(4-methoxyphenyl)methanone 3e. 60.6 mg, 50%. Solid, mp 143.7−144.6 °C (lit. 144−145 °C). IR (KBr): 3008, 1596, 1454, 1318, 1254, 1157, 925 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.90−

efficiently to produce carbonyls in moderate yields. The reaction also revealed more comprehensive application scopes of organoselenium catalysis and largely contributed to the development of this unique research direction.

4. EXPERIMENTAL SECTION 4.1. General Methods. Reagents were purchased from the merchant with their purities more than 98% and were directly used as received. Solvents were analytical pure (AR) and directly used without any special treatment. Diselenides were commercially available or prepared according to literature methods.4d,16 GC analysis was performed on a JieDao TECH GC1690 instrument. GC yields of the reactions were determined according to the internal standard curve by using biphenyl as the internal standard. Melting points were measured by a WRS-2A digital instrument. IR spectra were measured on a Bruker Tensor 27 Infrared spectrometer. 1H NMR spectra were recorded on a Bruker Avance instrument using CDCl3 as the solvent and Me4Si as the internal standard. Chemical shifts for 1H NMR were referred to internal Me4Si (0 ppm) and J-values were shown in Hz. Mass spectra were measured on a Shimadzu GCMS-QP2010 Ultra spectrometer (EI). 4.2. Typical Procedure for the Alkene Oxidations. To a 10-mL reaction tube, 0.5 mmol alkene and 0.025 mmol diselenide were added. H2O2 (2.5 mmol, 30 w/w% aqueous solution) in 2 mL of solvent was then injected by a syringe. The tube was equipped with condenser and heated (for reactions at temperature higher than 100 °C, the tube was sealed). The reaction was monitored by TLC. When the reaction terminated, the mixture was quenched by 2 mL of aqueous Na2SO3 (1 mol/L) and extracted by EtOAc (2 mL × 3). The combined organic layers were dried by Na2SO4 and the solvent was evaporated by a rotary evaporator. The residue was subjected to preparative TLC (eluent petroleum ether/EtOAc = 8:1) to produce 9347

DOI: 10.1021/acs.joc.7b01245 J. Org. Chem. 2017, 82, 9342−9349

Article

The Journal of Organic Chemistry 7.88 (m, 4H), 7.44−7.42 (m, 4H), 2.59 (s, 6H). 13C NMR (150 MHz, CDCl3 ): δ 194.5, 162.9, 132.2, 130.7, 113.5, 55.5. Known compound.17c Acetophenone 3f. 30.7 mg, 51% (70% GC yield). Oil. IR (film): 3065, 1687, 1595, 1443, 1360, 1263, 1171, 956, 762 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.94 (d, J = 7.8 Hz, 2H), 7.53 (t, J = 7.2 Hz, 1H), 7.43 (t, J = 7.8 Hz, 2H), 2.57 (s, 3H). 13C NMR (150 MHz, CDCl3): δ 198.1, 137.1, 133.1, 128.6, 128.3, 26.6. MS (EI, 70 eV) m/z (%): 121 (4) [M+ + 1], 120 (42) [M+], 105 (100), 77 (42). Known compound.17a Cyclohexyl(phenyl)methanone 3g. 58.7 mg, 62%. Solid, mp 50.8− 51.6 °C (lit. 52−53 °C). IR (KBr): 3012, 1670, 1592, 1448, 1387, 1226, 992, 703 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.94 (d, J = 8.4 Hz, 2H), 7.53 (t, J = 7.2 Hz, 1H), 7.45 (t, J = 7.2 Hz, 2H), 3.29− 3.24 (m, 1H), 1.90−1.83 (m, 4H), 1.73 (d, J = 12.6 Hz, 1H), 1.53− 1.40 (m, 2H), 1.39−1.35 (m, 2H), 1.31−1.23 (m, 1H). 13C NMR (150 MHz, CDCl3): δ 203.9, 136.3, 132.8, 128.6, 128.3, 45.6, 29.5, 26.0, 25.9. MS (EI, 70 eV) m/z (%): 189 (3) [M+ + 1], 188 (23) [M+], 105 (100), 83 (2). Known compound.17d Cyclopropyl(phenyl)methanone 3h. 36.6 mg, 50% (58% GC yield). Oil. 1H NMR (600 MHz, CDCl3, TMS): δ 7.90 (d, J = 7.8 Hz, 2H), 7.43 (t, J = 7.8 Hz, 1H), 7.34 (t, J = 7.8 Hz, 2H), 2.57−2.53 (m, 1H), 1.14−1.11 (m, 2H), 0.93−0.90 (m, 2H). 13C NMR (150 MHz, CDCl3): δ 200.7, 138.0, 132.8, 128.5, 128.0, 17.2, 11.7. MS (EI, 70 eV) m/z (%): 147 (3) [M+ + 1], 146 (22) [M+], 105 (100), 69 (4). Known compound.17d 1-(Naphthalen-1-yl)ethan-1-one 3i. 44.5 mg, 52%. Solid, mp 33.6−34.4 °C (lit. 34 °C). IR (KBr): 3052, 1681, 1508, 1433, 1353, 1189, 1075, 942, 785 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 8.76 (d, J = 9.0 Hz, 1H), 7.89 (d, J = 7.8 Hz, 1H), 7.83 (d, J = 7.2 Hz, 1H), 7.79 (d, J = 8.4 Hz, 1H), 7.56−7.53 (m, 1H), 7.46 (t, J = 7.2 Hz, 1H), 7.40−7.38 (m, 1H), 2.65 (s, 3H). 13C NMR (150 MHz, CDCl3): δ 201.8, 135.3, 134.0, 133.1, 130.2, 128.9, 128.5, 128.1, 126.5, 126.1, 124.4, 30.0. Known compound.17a 1-(4-Chlorophenyl)ethan-1-one 3j. 30.9 mg, 40% (52% GC yield). Oil. IR (film): 3006, 1689, 1587, 1402, 1358, 1261, 1096, 959, 830 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.88 (d, J = 9.0 Hz, 2H), 7.42 (d, J = 8.4 Hz, 2H), 2.58 (s, 3H). 13C NMR (150 MHz, CDCl3): δ 196.8, 139.5, 135.4, 129.7, 128.9, 26.6. MS (EI, 70 eV) m/z (%): 155 (2) [M+ + 1], 154 (27) [M+], 139 (100), 111 (53). Known compound.17a 1-(p-Tolyl)ethan-1-one 3k. 33.6 mg, 50% (66% GC yield). Oil. IR (film): 2925, 1684, 1608, 1418, 1358, 1265, 1179, 956, 817 cm−1. 1H NMR (600 MHz, CDCl3, TMS): δ 7.83 (d, J = 8.4 Hz, 2H), 7.22 (d, J = 7.8 Hz, 2H), 2.54 (s, 3H), 2.38 (s, 3H). 13C NMR (150 MHz, CDCl3): δ 197.8, 143.9, 134.7, 129.2, 128.4, 26.5, 21.6. MS (EI, 70 eV) m/z (%): 135 (3) [M+ + 1], 134 (28) [M+], 119 (100), 91 (61). Known compound.17a 2,3-Dihydro-1H-inden-1-one 3l. 31.7 mg, 48%. Solid, mp 41.6− 42.5 °C (lit. 41−42 °C). 1H NMR (600 MHz, CDCl3, TMS): δ 7.74 (d, J = 7.8 Hz, 1H), 7.57 (t, J = 7.2 Hz, 1H), 7.47 (d, J = 7.8 Hz, 1H), 7.35 (t, J = 7.8 Hz, 1H), 3.14−3.12 (m, 2H), 2.68−2.66 (m, 2H). 13C NMR (150 MHz, CDCl3): δ 207.1, 155.2, 137.0, 134.6, 127.3, 126.7, 123.6, 36.2, 25.8. MS (EI, 70 eV) m/z (%): 133 (7) [M+ + 1], 132 (100) [M+], 76 (9). Known compound.17a Benzaldehyde 3o. 22.3 mg, 21%. Oil. 1H NMR (600 MHz, CDCl3, TMS): δ 10.01 (s, 1H), 7.87 (d, J = 7.6 Hz, 2H), 7.61 (t, J = 7.0 Hz, 1H), 7.51 (t, J = 7.4 Hz, 2H). 13C NMR (150 MHz, CDCl3): δ 192.3, 136.4, 134.4, 129.7, 128.9. Known compound.17e Benzoic Acid 4. 31.7 mg, 26%. Solid, mp 122.1−122.2 °C (lit. 122.13 °C). 1H NMR (600 MHz, CDCl3, TMS): δ 13.02 (s, 1H), 8.13 (d, J = 7.2 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 2 H). 13 C NMR (150 MHz, CDCl3): δ 172.7, 133.8, 130.2, 129.3, 128.5. Known compound.17e Ethyl Benzoate 5. 34.5 mg, 23%. Oil. 1H NMR (600 MHz, CDCl3, TMS): δ 8.00 (d, J = 7.2 Hz, 2 H), 7.47 (t, J = 7.2 Hz, 1 H), 7.35 (d, J = 6.8 Hz, 2 H), 4.33−4.30 (m, 2 H), 1.33 (t, J = 7.0 Hz). 13C NMR (150 MHz, CDCl3): δ166.4, 132.7, 130.5, 129.4, 128.2, 60.8, 14.2. Known compound.17e

2-Ethoxy-2-phenylethan-1-ol 6. 34.9 mg, 42%. Oil. 1H NMR (600 MHz, CDCl3, TMS): δ 7.35−7.26 (m, 5H), 4.41 (m, 1H), 3.69−3.65 (m, 1H), 3.59 (m, 1H), 3.51−3.46 (m, 1H), 3.43−3.38 (m, 1H), 2.89 (s, 1H), 1.21 (t, J = 6.6 Hz, 3H). 13C NMR (150 MHz, CDCl3): δ 139.2, 128.5, 128.0, 126.8, 83.0, 67.3, 64.5, 15.3. Known compound.17f Ethyl 2-Phenylacetate 7. 12.3 mg, 15%. Oil. 1H NMR (600 MHz, CDCl3, TMS): δ 7.31−7.23 (m, 5H), 4.14−4.11 (m, 2H), 3.59 (s, 2H), 1.23 (t, J = 7.2 Hz, 3H). 13C NMR (150 MHz, CDCl3): δ 171.6, 134.2, 129.3, 128.6, 127.1, 60.9, 41.5, 14.2. Known compound.17g cis-1-Phenylcyclohexane-1,2-diol 8b. 21.2 mg, 22%. Solid, mp 91.1−92.3 °C (lit. 91.8−92.5 °C). 1H NMR (400 MHz, CDCl3, TMS): δ 7.52−7.26 (m, 5H), 4.08−4.00 (m, 1H), 3.07−3.04 (m, 1H), 1.91−1.39 (m, 8H). 13C NMR (100 MHz, CDCl3): δ 146.3, 128.5, 127.0, 125.1, 75.7, 74.5, 38.5, 29.2, 24.3, 21.1. MS (EI, 70 eV) m/z (%): 192 (38) [M+], 133 (82), 105 (100). Known compound.17h

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01245. Mass spectra of the detected byproducts, 1H and 13C NMR spectra of the products (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] ORCID

Lei Yu: 0000-0001-5659-7289 Author Contributions †

Authors T.W. and X.J. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by NNSFC (21202141), Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions, the Open Project Program of Jiangsu Key Laboratory of Zoonosis (R1509), and the High Level Talent Support Project of Yangzhou University. We thank the testing centre of Yangzhou University for assistance in analyses. We thank Changzhou Chen for assistance in experiments.

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