Organic Letters
Letter
5310−5316. (d) Li, H.; Zhao, Y.; Ma, L.; Ma, M.; Jiang, J.; Wan, X.
Radical-Carbene Coupling Reaction: Mn-Catalyzed Synthesis of
Indoles from Aromatic Amines and Diazo Compounds. Chem.
Commun. 2017, 53, 5993−5996. (e) Chen, R.; Zhao, Y.; Fang, S.;
Long, W.; Sun, H.; Wan, X. Coupling Reaction of Cu-Based Carbene
and Nitroso Radical: A Tandem Reaction to Construct Isoxazolines.
Org. Lett. 2017, 19, 5896−5899.
(6) (a) Ma, M.; Hao, W.; Ma, L.; Zheng, Y.; Lian, P.; Wan, X.
Interception of Radicals by Molecular Oxygen and Diazo Com-
pounds: Direct Synthesis of Oxalate Esters Using Visible-Light
Catalysis. Org. Lett. 2018, 20, 5799−5802. (b) Wang, Y.; Ma, L.; Ma,
M.; Zheng, H.; Shao, Y.; Wan, X. Bu4NI-Catalyzed Cross-Coupling
between Sulfonyl Hydrazides and Diazo Compounds to Construct β-
Carbonyl Sulfones Using Molecular Oxygen. Org. Lett. 2016, 18,
5082−5085. (c) Wang, N.-N.; Hao, W.-J.; Zhang, T.-S.; Li, G.; Wu,
Y.-N.; Tu, S.-J.; Jiang, B. Metal-Free C(sp3)−H Functionalization:
Oxidative Carbo-Oxygenation of a-Diazo Carbonyls via Radical
Dediazotization. Chem. Commun. 2016, 52, 5144−5147.
Wang, H.; Duan, X.-H. Metal-Free Oxidative HydroxyAlkylarylation
of Activated Alkenes by Direct sp3 C−H Functionalization of
Alcohols. Chem. Commun. 2013, 49, 7540−7542.
(13) (a) Li, P.; Zhao, J.; Xia, C.; Li, F. Direct Oxidative Coupling of
Enamides and 1,3-Dicarbonyl Compounds: A Facile and Versatile
Approach to Dihydrofurans, Furans, Pyrroles, and Dicarbonyl
Enamides. Org. Lett. 2014, 16, 5992−5995. (b) Ding, R.; Zhang,
Q.-C.; Xu, Y.-H.; Loh, T.-P. Preparation of Highly Substituted (β-
Acylamino)acrylates via Iron-Catalyzed Alkoxycarbonylation of N-
Vinylacetamides with Carbazates. Chem. Commun. 2014, 50, 11661−
11664.
(14) Jiang, J.; Liu, J.; Yang, L.; Shao, Y.; Cheng, J.; Bao, X.; Wan, X.
Cu-Based Carbene Involved in a Radical Process: a New Crossover
Reaction to Construct γ-Peroxy Esters and 1,4-Dicarbonyl Com-
pounds. Chem. Commun. 2015, 51, 14728−14731.
(15) (a) Zhao, J.; Li, P.; Xia, C.; Li, F. Direct N-Acylation of Azoles
via a Metal-Free Catalyzed Oxidative Cross-Coupling Strategy. Chem.
Commun. 2014, 50, 4751−4754. (b) Li, P.; Zhao, J.; Xia, C.; Li, F.
The Development of Carbene-Stabilized N−O Radical Coupling
Strategy in Metal-Free Regioselective C−H Azidation of Quinolone
N-Oxides. Org. Chem. Front. 2015, 2, 1313−1317. (c) Zhao, J.; Li, P.;
Xia, C.; Li, F. Metal-Free Regioselective C-3 Nitration of Quinolone
N-Oxides with Tert-Butyl Nitrite. RSC Adv. 2015, 5, 32835−32838.
(d) Zhao, J.; Li, P.; Li, X.; Xia, C.; Li, F. Straightforward Synthesis of
Functionalized Chroman-4-ones through Cascade Radical Cycliza-
tion-Coupling of 2-(Allyloxy)arylaldehydes. Chem. Commun. 2016,
52, 3661−3664. (e) Li, P.; Zhao, J.; Li, X.; Li, F. Alkali-Induced Ring-
Opening of 2-Amidodihydrofuran and Manganese Catalyzed Aerobic
Dehydrogenation Annulation: An Access to Functionalized Oxazole. J.
Org. Chem. 2017, 82, 4569−4577.
(16) Unhydrolyzed enamide intermediates (MW = 247.1) were
For a similar report on the hydrolysis of enamides, see: Hu, Z.; Tang,
Y.; Zhang, S.; Li, X.; Du, X.; Xu, X. MnO2-Catalyzed Oxidative
Alkylation of Enamides with Ethers via C(sp3)−H/C(sp2)−H Cross-
Dehydrogenative Coupling and Hydrolysis Sequence. Synlett 2015,
26, 2557−2560.
(7) Li, P.; Zhao, J.; Shi, L.; Wang, J.; Shi, X.; Li, F. Iodine-Catalyzed
Diazo Activation to Access Radical Reactivity. Nat. Commun. 2018, 9,
1972.
(8) We attempted an iodine-catalyzed diazoacetate activation
strategy under the thermal conditions or photoconditions, no 3aa
was detected, and the conversion of 1a was less than 5%, even using 1
equiv of I2 and 2 equiv of 2a.
(9) For selected examples on the synthesis of oxindoles through alkyl
radical addition to acrylamides, see: (a) Wei, W.-T.; Zhou, M.-B.; Fan,
J.-H.; Liu, W.; Song, R.-J.; Liu, Y.; Hu, M.; Xie, P.; Li, J.-H. Synthesis
of Oxindoles by Iron-Catalyzed Oxidative 1,2-Alkylarylation of
Activated Alkenes with an Aryl C(sp2)H Bond and a C(sp3)H
Bond Adjacent to a Heteroatom. Angew. Chem., Int. Ed. 2013, 52,
3638−3641. (b) Zhou, M.-B.; Wang, C.-Y.; Song, R.-J.; Liu, Y.; Wei,
W.-T.; Li, J.-H. Oxidative 1,2-Difunctionalization of Activated Alkenes
with Benzylic C(sp3)−H Bonds and Aryl C(sp2)−H Bonds. Chem.
Commun. 2013, 49, 10817−10819. (c) Wang, H.; Guo, L.-N.; Duan,
X.-H. Silver-Catalyzed Oxidative Coupling/Cyclization of Acryla-
mides with 1,3-Dicarbonyl Compounds. Chem. Chem. Commun.
2013, 49, 10370−10372. (d) Wang, H.; Guo, L.-N.; Duan, X.-H.
Metal-Free Oxidative Spirocyclization of Hydroxymethylacrylamide
with 1,3-Dicarbonyl Compounds: A New Route to Spirooxindoles.
Org. Lett. 2013, 15, 5254−5257. (e) Wang, H.; Guo, L.-N.; Duan, X.-
H. Palladium-Catalyzed Alkylarylation of Acrylamides with Unac-
tivated Alkyl Halides. J. Org. Chem. 2016, 81, 860−867. (f) Zhao, Y.;
Li, Z.; Sharma, U. K.; Sharma, N.; Song, G.; Van der Eycken, E. V.
Copper-Catalyzed Alkylarylation of Activated Alkenes Using Iso-
cyanides as the Alkyl Source: an Efficient Radical Access to 3,3-
Dialkylated Oxindoles. Chem. Commun. 2016, 52, 6395−6398.
(g) Xie, J.; Xu, P.; Li, H.; Xue, Q.; Jin, H.; Cheng, Y.; Zhu, C. A
Room Temperature Decarboxylation/C−H Functionalization Cas-
cade by Visible-Light Photoredox Catalysis. Chem. Commun. 2013, 49,
5672−5674. (h) Dai, Q.; Yu, J.; Jiang, Y.; Guo, S.; Yang, H.; Cheng, J.
The Carbomethylation of Arylacrylamides Leading to 3-Ethyl-3-
Substituted Indolin-2-one by Cascade Radical Addition/Cyclization.
Chem. Commun. 2014, 50, 3865−3867. (i) Li, Z.; Zhang, Y.; Zhang,
L.; Liu, Z.-Q. Free-Radical Cascade Alkylarylation of Alkenes with
Simple Alkanes: Highly Efficient Access to Oxindoles via Selective
(sp3)C−H and (sp2)C−H Bond Functionalization. Org. Lett. 2014,
16, 382−385. (j) Wang, S.; Huang, H.; Li, B.; Ge, Z.; Wang, X.; Li, R.
A Metal-Free Synthesis of Oxindoles by a Radical Addition-
Cyclization onto N-Arylacrylamides with Xanthates. Tetrahedron
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(10) Iodide catalysts only played a single electron transformation
role to assist the decomposition of hyperoxide, and not catalyzed
diazoacetates to generate carbene.
(11) The reaction did not work using tert-butyl alcohol, and the
result appears to indicate that the hydrogen abatraction is not direct
from the hydroxyl of alcohol.
(12) The byproduct 6 generated through radical A2 addition to 1a
was detected in 10% yield in our system; see: Meng, Y.; Guo, L.-N.;
E
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