Metal-Free Cascade Oxidative Decarbonylative Alkylation/Arylation of Alkynoates with Alphatic Aldehydes

Article abstract of DOI:10.1021/acs.joc.6b02451

The oxidative difunctionalization of aryl alkynoates with alphatic aldehydes as a cheap and abundant alkyl radical source was developed, providing a variety of trisubstituted alkenes in moderate to good yields. In this reaction, radical decarbonylative alkylation of C-C triple bond, 1,4-aryl migration, and decarboxylation were involved under metal-free conditions.

Full text of DOI:10.1021/acs.joc.6b02451

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Note
Metal-free Cascade Oxidative Decarbonylative Alkylation/
Arylation of Alkynoates with Alphatic Aldehydes
Changduo Pan, Yu Chen, Shuai Song, Lei Li, and Jin-Tao Yu
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 08 Nov 2016
Downloaded from http://pubs.acs.org on November 8, 2016
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The Journal of Organic Chemistry
Metal-free Cascade Oxidative Decarbonylative Alkylation/Arylation
of Alkynoates with Alphatic Aldehydes
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Changduo Pan,*,†,‡ Yu Chen,† Shuai Song,† Lei Li,† and Jin-Tao Yu*,‡
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†
School of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, P. R.
China
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‡
School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology,
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Changzhou University, Changzhou 213164, P. R. China
panchangduo@jsut.edu.cn; yujintao@cczu.edu.cn
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the
journal that you are submitting your paper to)
ABSTRACT
The oxidative difunctionalization of aryl alkynoates with alphatic aldehydes as cheap and abundant alkyl radical
source was developed, providing a variety of trisubstituted alkenes in moderate to good yields. In this reaction, radical
decarbonylative alkylation of C-C triple bond, 1,4-aryl migration, and decarboxylation were involved under metal-free
conditions.
Difunctionalization of the ubiquitous carbon-carbon triple bond is believed as a promising and convenient procedure
to generate various structural complex and synthetic useful compounds due to the readily availability of alkyne
derivatives.1 Among them, the radical oxidative coupling reactions have played important roles in synthetic organic
chemistry and offered many complementary methods to efficiently increase the molecular complexities.2 As a specific
case, activated alkynes such as alkynoates were widely utilized in organic synthesis. For example, Wu and coworkers
developed the construction of 3-acyl-4-arylcoumarins via metal-free tandem oxidative acylation/cyclization using
aldehydes as acyl radical source (eq (a), Scheme 1).3 Encouragingly, a great many of 3-functionalized coumarins were
successfully obtained by employing H-phosphonates, Togni’s reagent, ethyl bromodifluoroacetate, arylsulfinic
acids/sulfonyl hydrazides, AgSCF3 and AgSCN, α-keto acids, xanthates, N-iodosuccinimide, etc. as efficient radical
sources through oxidative radical addition and 6-endo/5-exo cyclization procedure.4 On the other hand, the
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copper-mediated radical addition to the carbon-carbon triple bond of alkynoates followed by dearomative
ipso-cyclization led to the products with an unexpected oxa-spiro skeleton.5 Radical aryl migration reactions are
common and promising strategy in organic synthesis.6 The 1,4-aryl migration was also involved in the
difunctionalization of alkynoates to furnish various trisubstituted olefins via oxidative radical addition/decarboxylation
procedure.7 In the later case, the direct functionalization of relative inert C(sp3)-H bonds were realized to generate alkyl,
benzylic, oxyalkyl, amidomethyl radicals. However, those alkylating reagents are limited to compounds with
symmetric structures or only one existing type of (activated) C(sp3)–H bond to reduce the possible regioisomers.
However, more convenient and efficient methods to provide structural complex alkyl radicals from readily available
source would be highly desirable.
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Aldehydes are cheap and readily available chemicals that can be easily converted into corresponding acyl radicals
for the acylation of various type of molecules.8 Moreover, they can also be employed as precursors for decarbonylative
reactions catalyzed by transition-metals.9 Recent studies revealed that the decarbonylation of aldehydes could also
occur in the absence of transition-metals to provide structural diversified aryl/alkyl radicals in the construction of C-C
bonds under the assistance of proper oxidants.10 As part of our ongoing interest in the direct difunctionalization of
alkynes,4c,7e,11 herein we report a general procedure involving the metal-free oxidative decarbonylative
alkylation/arylation of alkynoates using alphatic aldehydes as alkyl source to generate trisubstituted alkenes (eq (b),
Scheme 1).
Scheme 1. Difunctionalization of Alkynoates with Aldehydes
Our initial investigations focused on the optimization of the decarbonylative alkylation between diphenyl alkynoate
(1a) and pivalaldehyde (2a) (Table 1). In the presence of DTBP (di-tert-butyl peroxide), the desired decarbonylative
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alkylated product 3aa could be detected in DCE at 130 C for 20 h albeit in low yield (entry 1, Table 1). Inspired by
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this result, other solvents, such as acetonitrile, benzene, chlorobenzene, fluorobenzene, trifluoromethylbenzene and
DCM were investigated, and fluorobenzene was proved to be the best choice with an 85% yield of 3aa (entries 2-7,
Table 1). The utilization of proper oxidant was also crucial to the transformation, as TBHP, TBPB, DCP and BPO were
all inferior to DTBP (entries 8-11, Table 1). Additionally, the yield was sharply reduced under air or with less amount
of oxidant utilized (entry 5, Table 1). Temperature control experiment suggested that an obviously negative effect was
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observed at a lower temperature (110 C), while a higher temperature (140 C) didn’t result in better yield (entry 12,
Table 1).
Table 1. Screening the Optimized Reaction Conditions.a
Entry
1
Oxidant
Solvent
DCE
Yield (%)
DTBP
8
CH3CN
2
3
DTBP
DTBP
DTBP
DTBP
DTBP
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PhH
PhCl
PhF
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4
21
5
85 (62)b (66)c
PhCF3
DCM
PhF
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67
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16
DTBP
TBHP
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18
TBPB
DCP
PhF
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27
PhF
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12
70
23
BPO
PhF
68d (79)e(84)f
DTBP
PhF
a Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), oxidant (2 equiv) in solvent (2 mL) at 130 oC under N2 for 20 h. b under air. c DTBP
(1 equiv) was used. 110 C. 120 C. 140 C. DTBP = di-tert-butyl peroxide, TBHP = tert-butyl hydroperoxide, TBPB = tert-butyl
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peroxybenzoate, DCP = dicumyl peroxide, BPO = benzoyl peroxide.
Then, the generality of this oxidative decarbonylative alkylation of alkynoates with aliphatic aldehydes was
investigated. As expected, diaryl alkynoates with either electron-donating or electron-withdrawing substituents, such as
methyl, methoxyl, halogen and trifluoromethyl on either phenyl of alkynoates all reacted smoothly with pivalaldehyde
and successfully transformed into the desired 1,1-diaryl-2-tert-butyl ethylenes in moderate to good yields (3aa-3oa,
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Figure 1). In addition, volatile C-I bond and ester group were well tolerated to generate the corresponding products
(3ma & 3oa, Figure 1). Interestingly, alkynoates with meta-substitution on phenyls gave slightly lower yields
compared with substrates with para-substituted groups (3ga vs 3fa, 3ja vs 3ka, Figure 1). Unsymmetrical aryl
alkynoates were employed to examine the stereoselectivity of the reaction, giving the mixed E/Z isomers (3ia–3oa,
Figure 1),
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Figure 1. Scope of the Alkynoates.a
a Reaction conditions: 1 (0.2 mmol), 2a (0.4 mmol, 2 equiv), DTBP (2 equiv) in PhF (2 mL) at 130 oC under N2 for 20 h. b The ratio of the
isomers was determined by 1H NMR.
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Apart from pivalaldehyde, other secondary alkyl aldehydes, such as isobutyraldehyde (2b), 2-ethylbutanal (2c),
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2-methylbutanal (2d), 2-methylpentanal (2e), cyclohexanecarbaldehyde (2f) and 2-phenylpropanal (2g) were also good
choices of secondary alkyl radical sources to produce the corresponding 1,1-diphenyl-2-alkyl ethylenes in moderate to
good yields (3ab-3ag, Figure 2). Unfortunately, attempts to utilize primary alkyl aldehydes, such as hexaldehyde,
failed to deliver the desired product. It is worth to note that, although our procedure was similar with Wu’s,3 no
3-acylated coumarin was detected, which may be due to the relatively higher temperature in our current procedure.
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Figure 2. Scope of Alphatic Aldehydes.a
a Reaction conditions: 1a (0.2 mmol), 2 (0.4 mmol), DTBP (2 equiv) in PhF (2 mL) at 130 oC under N2 for 20 h.
Scheme 2. Mechanism Studies.
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Finally, control experiments were conducted to gain insights into the reaction mechanism as shown in Scheme 2.
The transformation was completely inhibited when 2,2,6,6-tetramethylpiperidinooxy (TEMPO) was added to the
reaction as radical scavenger under standard conditions (eq 1, Scheme 2). The addition of BHT
(2,6-di-tert-butyl-4-methylphenol) also effectively suppressed the reaction with the adduct formed by BHT and
tert-butyl radical detected by GC-MS analysis (eq 1, Scheme 2). These results indicated radical intermediates were
involved.
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Based on the above experimental results and former reported works, the mechanism was outlined in Scheme 3.
Firstly, the thermol homolytic cleavage of DTBP forms a tert-butoxy radical, which abstracts the hydrogen atom from
aldehyde to provide tert-butyl alcohol and acyl radical A. Then, A undergoes decarbonylation to release CO and
produce the tert-butyl radical B, which selectively adds to the α-carbon of the C−C triple bond in alkynoate 1a and
gives an active vinyl radical C. Next, the intramolecular radical ipso-cyclization of C forms a spiro intermediate D,
which readily undergoes 1,4-aryl migration and subsequent decarboxylation affording another vinyl intermediate F and
CO2. Finally, F abstracts hydrogen from aldehyde 2 to generate product 3 as well as the acyl radical A.
Scheme 3. The Proposed Mechanism.
In summary, we have developed a metal-free cascade oxidative decarbonylative alkylation of diaryl alkynoates with
aliphatic aldehydes to provide a series of trisubstituted olefins in moderate to good yields. The subsequent
decarbonylation, radical addition, 1,4-aryl migration and decarboxylation processes were involved with the cascade
cleavage of C(sp3)–C(sp2), C(sp2)-O, C(sp2)–C(sp2) bonds and the construction of C(sp3)–C(sp2) and C(sp2)–C(sp2)
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bonds in one-pot. This procedure offers a new complementary to the convenient generation of 1,1-diaryl-2-alkyl
ethylenes using alphatic aldehydes as cheap and abundant alkyl radical source.
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EXPERIMENTAL SECTION
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General Information: All chemicals were used as received without further purification unless stated otherwise.
NMR spectra were recorded at ambient temperature on a 300 or 400 M NMR spectrometer. Chemical shifts (δ) are
given in ppm relative to TMS, the coupling constants J are given in Hz. HRMS were recorded on a TOF LC/MS
equipped with electrospray ionization (ESI) probe operating in positive or negative ion mode. IR spectra were recorded
on a spectrometer using KBr disks.
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Experimental General Procedure for the Reaction: Under N2, the mixture of alkynoate 1 (0.2 mmol), aliphatic
aldehyde 2 (0.4 mmol), DTBP (0.4 mmol, 58.5 mg) and PhF (2 mL) were added into the tube and sealed. The reaction
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mixture was vigorously stirred at 130 C for 20 h. Then, the solvent was evaporated under reduced pressure and the
residue was purified by flash column chromatography on silica gel to afford the products.
(3,3-Dimethylbut-1-ene-1,1-diyl)dibenzene (3aa). 9f Flash column chromatography on silica gel (petroleum ether)
gave a colorless oil (40.1 mg, 85%). 1H NMR (CDCl3, 400 MHz): δ 7.39-7.32 (m, 3H), 7.27-7.18 (m, 7H), 6.11 (s, 1H),
0.99 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 144.1, 140.8, 140.1, 139.0, 130.4, 128.0, 127.8, 126.9, 126.7, 126.6,
34.0, 31.3.
4,4'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis(methylbenzene) (3ba). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (36.9 mg, 70%). 1H NMR (CDCl3, 300 MHz): δ 7.17-7.04 (m, 8H), 6.05 (s, 1H),
2.39 (s, 3H), 2.31 (s, 3H), 0.98 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 141.6, 139.2, 138.8, 137.9, 136.2, 130.2,
129.1, 128.9, 128.8, 128.7, 128.6, 128.4, 128.1, 126.7, 33.9, 31.4, 21.3, 21.0. IR (cm−1): ν 3021, 2956, 2922, 2865,
1654, 1630, 1509, 1473, 1459, 1362, 1249, 1188, 1021. HRMS (ESI): m/z calcd for C20H25 (M+H)+ 265.1951, found
265.1950.
3,3'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis(methoxybenzene) (3ca). Flash column chromatography on silica gel
(petroleum ether/ethyl acetate 100/1) gave a colorless oil (37.3 mg, 63%). 1H NMR (CDCl3, 400 MHz): δ 7.29 (d, J =
6.9 Hz, 1H), 7.21-7.17 (m, 1H), 6.89-6.75 (m, 6H), 6.11 (s, 1H), 3.83 (s, 3H), 3.79 (s, 3H), 1.01 (s, 9H). 13C{1H} NMR
(CDCl3, 75 MHz): δ 159.3, 159.1, 145.4, 141.9, 140.1, 138.6, 128.9, 128.7, 122.9, 119.5, 115.9, 113.1, 112.3, 111.5,
55.2, 33.9, 31.2. IR (cm−1): ν 3024, 2956, 2865, 2834, 1734, 1653, 1596, 1577, 1485, 1463, 1364, 1284, 1239, 1213,
1165, 1050. HRMS (ESI): m/z calcd for C20H25O2 (M+H)+ 297.1849, found 297.1851.
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4,4''-(3,3-Dimethylbut-1-ene-1,1-diyl)di-1,1'-biphenyl (3da). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (56.6 mg, 73%). 1H NMR (CDCl3, 300 MHz): δ 7.72-7.59 (m, 6H), 7.54-7.41 (m,
7H), 7.38-7.32 (m, 5H), 6.23 (s, 1H), 1.06 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 143.1, 140.9, 140.8, 140.5,
139.8, 139.6, 139.5, 138.3, 130.8, 128.8, 128.78, 128.72, 127.3, 127.2, 127.04, 127.01, 126.8, 126.5, 34.1, 31.4. IR
(cm−1): ν 3025, 3027, 2957, 2927, 2863, 1734, 1654, 1609, 1486, 1462, 1447, 1359, 1247, 1190, 1007. HRMS (ESI):
m/z calcd for C30H29 (M+H)+ 389.2264, found 389.2266.
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4,4'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis(fluorobenzene) (3ea). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (47.3 mg, 87%). 1H NMR (CDCl3, 300 MHz): δ 7.17-7.10 (m, 4H), 7.08-7.02 (m,
2H), 6.95-6.89 (m, 2H), 6.04 (s, 1H), 0.97 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 163.5 (d, JC-F = 6.0 Hz), 160.3
(d, JC-F = 5.3 Hz), 140.5, 140.0 (d, JC-F = 3.0 Hz), 137.0, 136.4 (d, JC-F = 3.5 Hz), 131.7 (d, JC-F = 7.5 Hz), 128.4 (d,
JC-F = 6.8 Hz), 115.0 (d, JC-F = 4.5 Hz), 114.7 (d, JC-F = 5.3 Hz), 34.0, 31.3. IR (cm−1): ν 3031, 2959, 2927, 2868, 1656,
1600, 1508, 1480, 1461, 1367, 1223, 1158, 1053. HRMS (ESI): m/z calcd for C18H19F2 (M+H)+ 273.1449, found
273.1450.
4,4'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis(chlorobenzene) (3fa).12 Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (54.7 mg, 90%). 1H NMR (CDCl3, 300 MHz): δ 7.35-7.32 (m, 2H), 7.23-7.21 (m,
1H), 7.20-7.18 (m, 1H), 7.14-7.05 (m, 4H), 6.08 (s, 1H), 0.97 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 142.1, 141.2,
138.8, 136.8, 133.0, 132.6, 131.6, 130.4, 129.5, 128.5, 128.4, 128.2, 128.17, 128.12, 34.1, 31.3.
3,3'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis(chlorobenzene) (3ga). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (48.6 mg, 80%). 1H NMR (CDCl3, 300 MHz): δ 7.32-7.29 (m, 2H), 7.19-7.17 (m,
4H), 7.10-7.07 (m, 1H), 7.03-6.99 (m, 1H), 6.09 (s, 1H), 0.98 (s, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 145.3, 142.0,
141.9, 136.6, 134.1, 133.9, 130.2, 129.3, 129.2, 128.5, 127.3, 126.9, 126.8, 125.2, 34.2, 31.2. IR (cm−1): ν 3062, 2959,
2902, 2866, 1654, 1589, 1562, 1473, 1363, 1278, 1244, 1160, 1095, 1078. HRMS (ESI): m/z calcd for C18H19Cl2
(M+H)+ 305.0858, found 305.0862.
4,4'-(3,3-Dimethylbut-1-ene-1,1-diyl)bis((trifluoromethyl)benzene) (3ha). Flash column chromatography on
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silica gel (petroleum ether) gave a colorless oil (61.7 mg, 83%). H NMR (CDCl3, 300 MHz): δ 7.63 (d, J = 7.9 Hz,
2H), 7.49 (d, J = 8.2 Hz, 2H), 7.32 (d, J = 7.9 Hz, 2H), 7.23 (d, J = 8.1 Hz, 2H), 6.19 (s, 1H), 0.97 (s, 9H). 13C{1H}
NMR (CDCl3, 75 MHz): δ 146.7, 143.9, 143.1, 136.8, 130.6, 129.4, 129.2 (q, JC-F = 32.2 Hz), 128.5, 125.9, 125.4 (q,
JC-F = 3.7 Hz), 125.1 (q, JC-F = 3.7 Hz), 125.0 (q, JC-F = 3.7 Hz), 34.3, 31.2. IR (cm−1): ν 3065, 2962, 2912, 2870, 1662,
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1613, 1574, 1465, 1324, 1248, 1166, 1127, 1068, 1017. HRMS (ESI): m/z calcd for C20H19F6 (M+H)+ 373.1385, found
373.1382.
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1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-4-ethylbenzene (3ia). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (34.3 mg, 65%). 1H NMR (CDCl3, 300 MHz): δ 7.38-7.16 (m, 6H), 7.14-7.04 (m,
3H), 6.08 (d, 1H), 2.73-2.66 (q, 1H), 2.65-2.57 (q, 1H), 1.28 (t, J = 7.6 Hz, 1H), 1.21 (t, J = 7.6 Hz, 1H), 0.98 (s, 4.5H),
0.97 (s, 4.5H). 13C{1H} NMR (CDCl3, 75 MHz): δ 144.4, 142.7, 142.6, 141.5, 140.9, 140.1, 139.3, 139.1, 137.9, 130.3,
130.2, 127.9, 127.7, 127.5, 127.2, 126.9, 126.7, 126.6, 126.5, 34.0, 33.9, 31.4, 28.6, 28.4, 15.6, 15.5. IR (cm−1): ν 3021,
2960, 2929, 2867, 1654, 1630, 1597, 1508, 1474, 1460, 1443, 1362, 1249, 1189, 1029. HRMS (ESI): m/z calcd for
C20H25 (M+H)+ 265.1951, found 265.1950.
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1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-4-methoxybenzene (3ja).13 Flash column chromatography on silica gel
(petroleum ether/ethyl acetate 100/1) gave a colorless oil (40.9 mg, 77%). 1H NMR (CDCl3, 300 MHz): δ 7.36-7.15 (m,
5H), 7.12-7.07 (m, 2H), 6.87 (d, J = 8.7 Hz, 1H), 6.77 (d, J = 8.7 Hz, 1H), 6.06 (s, 0.44H), 5.99 (s, 0.47H), 3.82 (s,
1.4H), 3.76 (s, 1.58H), 0.97 (s, 4.62H), 0.94 (s, 4.39H). 13C{1H} NMR (CDCl3, 75 MHz): δ 158.5, 158.4, 144.4, 141.0,
140.3, 138.7, 138.5, 138.4, 136.8, 132.9, 131.4, 130.3, 128.0, 127.9, 127.7, 126.9, 126.7, 126.5, 113.4, 113.2, 55.3,
55.2, 33.9, 33.8, 31.4, 31.3.
1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-3-methoxybenzene (3ka). Flash column chromatography on silica gel
(petroleum ether/ethyl acetate 100/1) gave a colorless oil (36.7 mg, 69%). 1H NMR (CDCl3, 300 MHz): δ 7.36-7.12 (m,
6H), 6.86-6.70 (m, 3H), 6.09 (s, 0.5H), 6.06 (s, 0.5H), 3.79 (s, 1.5H), 3.74 (s, 1.5H), 0.98 (s, 4.5H), 0.95 (s, 4.5H).
13C{1H} NMR (CDCl3, 75 MHz): δ 159.3, 159.1, 145.7, 143.8, 142.1, 140.6, 140.3, 140.0, 138.84, 138.80, 130.3,
128.9, 128.7, 128.0, 127.8, 126.8, 126.6, 123.0, 119.5, 115.9, 113.1, 112.2, 111.5, 55.2, 55.1, 34.0, 33.9, 31.3, 31.2. IR
(cm−1): ν 3057, 2952, 2865, 1654, 1633, 1596, 1577, 1486, 1463, 1429, 1363, 1285, 1226, 1139, 1051. HRMS (ESI):
m/z calcd for C19H23O (M+H)+ 267.1743, found 267.1744.
1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-4-fluorobenzene (3la). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (43.7 mg, 86%). 1H NMR (CDCl3, 300 MHz): δ 7.36-7.10 (m, 7H), 7.03 (t, J =
8.7 Hz, 1H), 6.90 (t, J = 8.7 Hz, 1H), 6.09 (s, 0.5H), 6.01 (s, 0.5H), 0.96-0.95 (d, 9H). 13C{1H} NMR (CDCl3, 75 MHz):
δ 163.5 (d, JC-F = 6.7 Hz), 160.2 (d, JC-F = 6.9 Hz), 143.8 (d, JC-F = 0.6 Hz), 140.7, 140.6, 140.2 (d, JC-F = 3.1 Hz),
139.9 (d, JC-F = 1.3 Hz), 138.0 (d, JC-F = 11.1 Hz), 136.5 (d, JC-F = 3.5 Hz), 131.8 (d, JC-F = 7.8 Hz), 130.2, 128.4, 128.3,
128.1, 127.9, 126.9, 126.8, 126.7, 114.8 (d, JC-F = 1.7 Hz), 114.6 (d, JC-F = 1.7 Hz), 34.0, 33.9, 31.33, 31.30. IR (cm−1):
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ν 3051, 3020, 2958, 2924, 2865, 1654, 1631, 1507, 1474, 1460, 1443, 1363, 1221, 1157, 1029, 1014. HRMS (ESI): m/z
calcd for C18H20F (M+H)+ 255.1544, found 255.1546.
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1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-4-iodobenzene (3ma). Flash column chromatography on silica gel
(petroleum ether) gave a colorless oil (52.8 mg, 73%). 1H NMR (CDCl3, 300 MHz): δ 7.67 (d, J = 8.4 Hz, 1H), 7.53 (d,
J = 8.6 Hz, 1H), 7.34-7.29 (m, 1H), 7.25-7.12 (m, 4H), 6.96-6.89 (m, 2H), 6.08 (s, 0.5H), 6.06 (s, 0.5H), 0.96 (s, 4.5H),
0.94 (s, 4.5H). 13C{1H} NMR (CDCl3, 75 MHz): δ 143.7, 143.5, 140.7, 140.6, 140.4, 140.1, 138.2, 137.9, 137.2, 137.0,
136.9, 132.3, 130.3, 128.8, 128.2, 128.1, 127.9, 127.0, 126.9, 126.8, 92.4, 92.1, 34.1, 34.0, 31.4, 31.2. IR (cm−1): ν
3056, 3021, 2957, 2926, 2864, 1653, 1633, 1597, 1491, 1481, 1460, 1443, 1386, 1359, 1246, 1188, 1059, 1006. HRMS
(ESI): m/z calcd for C18H20I (M+H)+ 363.0604, found 363.0609.
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1-(3,3-Dimethyl-1-phenylbut-1-en-1-yl)-4-(trifluoromethyl)benzene (3na). Flash column chromatography on
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silica gel (petroleum ether) gave a colorless oil (51.7 mg, 85%). H NMR (CDCl3, 300 MHz): δ 7.60 (d, J = 7.9 Hz,
1H), 7.46 (d, J = 8.2 Hz, 1H), 7.38-7.28 (m, 3H), 7.26-7.11 (m, 4H), 6.14 (s, 0.5H), 6.13 (s, 0.45H), 0.97 (s, 4.59H),
0.95 (s, 4.42H). 13C{1H} NMR (CDCl3, 75 MHz): δ 147.6, 144.8, 143.2, 142.2, 141.0, 139.9, 138.1, 137.7, 130.7,
130.3, 129.6 (q, JC-F = 6.0 Hz), 129.4, 129.2, 128.5 (q, JC-F = 6.0 Hz), 128.2, 128.0, 126.1 (q, JC-F = 2.2 Hz), 125.2 (q,
JC-F = 3.7 Hz), 124.9 (q, JC-F = 3.7 Hz), 124.7 (q, JC-F = 3.7 Hz), 122.5, 34.2, 34.0, 31.3, 31.1. IR (cm−1): ν 3056, 3022,
2960, 2867, 1615, 1493, 1474, 1407, 1364, 1325, 1165, 1125, 1067, 1016. HRMS (ESI): m/z calcd for C19H20F3
(M+H)+ 305.1512, found 305.1515.
Ethyl 4-(3,3-dimethyl-1-phenylbut-1-en-1-yl)benzoate (3oa). Flash column chromatography on silica gel
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(petroleum ether/ethyl acetate 50/1) gave a colorless oil (48.7 mg, 79%). H NMR (CDCl3, 300 MHz): δ 8.03 (d, J =
8.4 Hz, 1H), 7.89 (d, J = 8.6 Hz, 1H), 7.38-7.12 (m, 7H), 6.18-6.11 (d, 1H), 4.42-4.30 (m, 2H), 1.41 (t, J = 7.1 Hz,
1.5H), 1.36 (t, J = 7.1 Hz, 1.5H), 0.97-0.96 (d, 9H). 13C{1H} NMR (CDCl3, 75 MHz): δ 166.6, 166.5, 148.5, 145.9,
143.3, 142.0, 140.7, 140.0, 138.5, 138.1, 130.4, 130.3, 129.3, 129.1, 129.0, 128.4, 128.3, 128.1, 127.9, 127.0, 126.8,
126.7, 60.9, 60.8, 34.2, 34.0, 31.3, 31.2, 14.4, 14.3. IR (cm−1) ν 3057, 2958, 2905, 2868, 1717, 1606, 1491, 1474, 1463,
1444, 1403, 1365, 1274, 1175, 1101, 1021. HRMS (ESI): m/z calcd for C21H25O2 (M+H)+ 309.1849, found 309.1850.
(3-Methylbut-1-ene-1,1-diyl)dibenzene (3ab).14 Flash column chromatography on silica gel (petroleum ether) gave
a colorless oil (34.2 mg, 77%). 1H NMR (CDCl3, 300 MHz): δ 7.40-7.26 (m, 3H), 7.25-7.12 (m, 7H), 5.89 (d, J = 10.1
Hz, 1H), 2.50-2.38 (m, 1H), 1.01 (t, J = 6.6 Hz, 6H). 13C{1H} NMR (CDCl3, 75 MHz): δ 142.7, 140.5, 139.1, 137.3,
129.8, 128.1, 128.0, 127.1, 126.8, 126.7, 28.8, 23.3.
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(3-Ethylpent-1-ene-1,1-diyl)dibenzene (3ac).9f Flash column chromatography on silica gel (petroleum ether) gave
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a colorless oil (40 mg, 80%). H NMR (CDCl3, 300 MHz): δ 7.38-7.28 (m, 3H), 7.26-7.14 (m, 7H), 5.82 (d, J = 10.5
Hz, 1H), 2.08-1.96 (m, 1H), 1.48-1.34 (m, 2H), 1.32-1.25 (m, 2H), 0.84 (t, J = 7.4 Hz, 6H). 13C{1H} NMR (CDCl3, 75
MHz): δ 142.8, 141.7, 140.8, 134.9, 130.0, 128.1, 127.0, 126.7, 126.6, 42.2, 28.5, 12.0.
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(3-Methylpent-1-ene-1,1-diyl)dibenzene (3ad).9f Flash column chromatography on silica gel (petroleum ether)
gave a colorless oil (35.9 mg, 76%). 1H NMR (CDCl3, 300 MHz): δ 7.39-7.28 (m, 3H), 7.27-7.14 (m, 7H), 5.85 (d, J =
10.3 Hz, 1H), 2.27-2.12 (m, 1H), 1.39-1.29 (m, 2H), 0.99 (d, J = 6.7 Hz, 3H), 0.83 (t, J = 7.4 Hz, 3H). 13C{1H} NMR
(CDCl3, 75 MHz): δ 142.4, 140.7, 140.3, 136.2, 129.8, 128.2, 128.1, 127.1, 126.8, 126.7, 35.5, 30.4, 21.1, 12.0.
(3-Methylhex-1-ene-1,1-diyl)dibenzene (3ae). Flash column chromatography on silica gel (petroleum ether) gave a
colorless oil (37 mg, 74%). 1H NMR (CDCl3, 300 MHz): δ 7.39-7.28 (m, 3H), 7.27-7.14 (m, 7H), 5.85 (d, J = 10.3 Hz,
1H), 2.34-2.24 (m, 1H), 1.35-1.16 (m, 4H), 1.00 (d, J = 6.6 Hz, 3H), 0.-0.79 (t, J = 6.9 Hz, 3H). 13C{1H} NMR (CDCl3,
75 MHz): δ 142.7, 140.6, 140.0, 136.4, 129.8, 128.1, 128.0, 127.0, 126.7, 40.0, 33.6, 21.5, 20.7, 14.2. IR (cm−1): ν
3057, 3023, 2956, 2924, 2869, 1653, 1598, 1562, 1494, 1455, 1444, 1377, 1072, 1031. HRMS (ESI): m/z calcd for
C19H23 (M+H)+ 251.1794, found 251.1795.
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(2-Cyclohexylethene-1,1-diyl)dibenzene (3af).9f Flash column chromatography on silica gel (petroleum ether) gave
a colorless oil (36.7 mg, 70%). 1H NMR (CDCl3, 300 MHz): δ 7.39-7.26 (m, 3H), 7.25-7.16 (m, 7H), 5.89 (d, J = 10.0
Hz, 1H), 2.14-2.05 (m, 1H), 1.69-1.60 (m, 5H), 1.22-1.11 (m, 5H). 13C{1H} NMR (CDCl3, 75 MHz): δ 142.9, 140.6,
139.5, 136.0, 129.8, 128.1, 128.0, 127.2, 126.8, 126.7, 38.3, 33.3, 26.0, 25.6.
But-1-ene-1,1,3-triyltribenzene (3ag).9f Flash column chromatography on silica gel (petroleum ether) gave a
colorless oil (46.6 mg, 82%). 1H NMR (CDCl3, 300 MHz): δ 7.41-7.29 (m, 4H), 7.25-7.13 (m, 11H), 5.89 (d, J = 10.4
Hz, 1H), 3.65-3.54 (m, 1H), 1.38 (d, J = 6.9 Hz, 1H). 13C{1H} NMR (CDCl3, 75 MHz): δ 146.2, 142.4, 140.2, 140.1,
134.2, 129.8, 128.5, 128.3, 128.1, 127.3, 127.1, 127.0, 126.9, 126.0, 39.3, 22.4.
ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China (21602086 and 21672028), the Natural Science
Foundation for Colleges and Universities of Jiangsu Province (16KJB150002) and Jiangsu Key Laboratory of
Advanced Catalytic Materials & Technology (BM2012110) for financial supports.
Supporting Information:
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Mechanism study, 1H and 13C NMR spectra of compounds 3aa-3oa, 3ab-3ag. This material is available free of charge
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via the Internet at http://pubs.acs.org.
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