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Synthesis of carbamates
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A copper-based photoredox catalyst, bearing a tridentate carbazolide/bisphosphine
ligand, that can be activated upon irradiation by blue LEDs, achieves the
coupling of a range of primary carbamates with unactivated secondary alkyl
bromides at room temperature.
J. M. Ahn, J. C. Peters, G. C. Fu, J. Am. Chem. Soc., 2017,
139, 18101-18106.
The arylation of N-H and O-H containing compounds at room temperature with
phenylboronic acids is promoted in the presence of cupric acetate and a tertiary
amine. Substrates include phenols, amines, anilines, amides, imides, ureas,
carbamates, and sulfonamides.
D. M. T. Chan, K. L. Monaco, R.-P. Wang, M. P. Winteres, Tetrahedron Lett.,
1998, 39, 2933-2936.
A highly efficient Ni(II)-catalyzed
photoredox N-arylation of Cbz-amines/Boc-amines with aryl electrophiles at room
temperature provides a wide
variety of N-aromatic and N-heteroaromatic carbamate products that find use in
the synthesis of several biologically active molecules. The reaction offers a
viable alternative to traditional palladium-catalyzed Buchwald-Hartwig reaction.
L. R. Reddy, S. Kotturi, Y. Waman, V. R. Reddy, C. Patel, A. Kobarne, S.
Kuttappan, J. Org. Chem., 2018, 83,
13854-13860.
An efficient synthesis of aryl carbamates - including major carbamate protecting
groups - was achieved by introducing alcohols into the reaction of
palladium-catalyzed cross-coupling of aryl chlorides and triflates with sodium
cyanate. This methodology also provides direct access to S-thiocarbamates
and diisocyanate precursors to polyurethane materials.
E. V. Vinogradova, N. H. Park, B. P. Fors, S. L. Buchwald, Org. Lett., 2013,
15, 1394-1397.
A CuI/MNAO [2-((2-methylnaphthalen-1-yl)amino)-2-oxoacetic acid] catalyzed
cross-coupling of (hetero)aryl chlorides with potassium cyanate in alcohols
provides N-(hetero)aryl carbamates in very good yields at 120-130°C.
Moreover, (hetero)aryl bromides and (hetero)aryl iodides were reacted at lower
catalyst loadings and lower temperatures.
S. V. Kumar, D. Ma, J. Org. Chem., 2018, 83,
2706-2713.
The reaction of azidoformates with boronic acids in the presence of 10 mol% of
copper chloride enables a mild and efficient synthesis of N-arylcarbamates
in an open flask at room temperature without additional base, ligand, or
additive. A subsequent reaction with aluminum-amine complexes in a two-step
one-pot procedure gives N-arylcarbamates.
S.-Y. Moon, U. Bin Kim, D.-B. Sung, W.-S. Kim, J. Org. Chem.,
2015,
80, 1856-1865.
The use of PhINTs as a reagent enables a mild Hofmann rearrangement of aromatic
and aliphatic carboxamides. The mild reaction conditions and high selectivity in
the reaction of carboxamides with PhINTs allow the isolation of the initially
formed labile isocyanates or their subsequent conversion to stable carbamates by
treatment with alcohols.
A. Yoshimura, M. W. Luedtke, V. V. Zhdankin, J. Org. Chem., 2012,
77, 2087-2091.
An intramolecular decarboxylation of readily prepared alkanoyloxycarbamates
enables a general and effective synthesis of primary and secondary alkylamines.
The reaction tolerates a broad range of functional groups and the corresponding
products were obtained in good yields under mild conditions.
P. Li, N. Ma, Z. Wang, Q. Dai, C. Hu, J. Org. Chem., 2018, 83,
8233-8240.
Catalysts generated from Pd2(dba)3 and biphenyl ligands efficiently
promote the coupling of amides and carbamates with unactivated vinyl triflates
and tosylates, to provide enamides in good to excellent yields.
M. C. Willis, G. N. Brace, I. P. Holmes,
Synthesis, 2005, 3229-3234.
A mild palladium-catalyzed conjugate addition of a carbamate nucleophile to an
enone provides β-amido ketones in very good yields. The regiocontrol, neutral
conditions, and lack of preactivation of the nucleophile are attractive features
of this transformation.
M. J. Gaunt, J. B. Spencer,
Org. Lett., 2001, 3, 25-28.
The AuCl3-PPh3-catalyzed direct
three-component Mannich reactions of aryl aldehydes, aryl ketones, and
carbamates led to N-protected β-aryl-β-amino ketones.
L.-W. Xu, C.-G. Xia, L. Li, J. Org. Chem.,
2004,
69, 8482-8484.
A direct reaction between carbamates and achiral allylic carbonates to form
branched, conveniently protected primary allylic amines with high
regioselectivity and enantioselectivity occurs without base in the presence of a
metalacyclic iridium catalyst containing a labile ethylene ligand.
D. J. Weix, D. Marković, M. Ueda, J. F. Hartwig, Org. Lett., 2009,
11, 2944-2947.
Iridium-catalyzed allylation of potassium trifluoroacetamide or the highly
reactive ammonia equivalent lithium di-tert-butyliminodicarboxylate forms
a range of conveniently protected, primary, α-branched allylic amines in high
yields, high branched-to-linear regioselectivities, and high enantiomeric excess.
M. J. Pouy, A. Leitner, D. J. Weix, S. Ueno, J. F. Hartwig, Org. Lett., 2007,
9, 3949-3952.
Alkylcarboxamides can be converted to the respective alkylcarbamates by
Hofmann rearrangement using hypervalent iodine species generated in situ from
PhI and Oxone in methanol. In addition, substituted benzamides can be converted
to the respective quinone derivatives by treatment with Oxone and iodobenzene in
aqueous acetonitrile.
A. A. Zagulyaeva, C. T. Banek, M. S. Yusubov, V. V. Zhdankin, Org. Lett., 2010,
12, 4644-4647.
Hofmann rearrangement of carboxamides to carbamates using Oxone as an oxidant
can be efficiently catalyzed by iodobenzene via hypervalent iodine species
generated in situ in the presence of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) in
aqueous methanol solutions. Under these conditions, Hofmann rearrangement of
various carboxamides affords corresponding carbamates in high yields.
A. Yoshimura, K. R. Middleton, M. W. Luedtke, C. Zhu, V. V. Zhdankin, J. Org. Chem., 2012,
77, 11399-11404.
A versatile and efficient
copper-catalyzed amidation of vinyl bromides and iodides has been developed.
The protocol, which uses a combination of copper iodide and N,N'-dimethyl
ethylenediamine, tolerates substrates bearing ester, silyl ether, and amino
groups.
L. Jiang, G. E. Job, A. Klapars, S. L. Buchwald, Org.
Lett., 2003, 5, 3667-3669.
A mild, ruthenium-catalyzed anti-Markovnikov addition of secondary amides,
anilides, lactames, ureas, bislactames, and carbamates to terminal alkynes
has been developped. Two complementary protocols provide either the E
or the Z isomers.
L. J. Goossen, J. E. Rauhaus, G. Deng, Angew. Chem. Int. Ed., 2005,
44, 4042-4045.
A range of enol triflates can be coupled with amides, carbamates, and
sulfonamides using palladium catalysis. This method allows the synthesis of
enamides, which may not be readily available by other means.
D. J. Wallace, D. J. Klauber, C.-Y. Chen, R. P.
Volante, Org. Lett., 2003, 5, 4749-4752.
Silyl carbamates undergo allylation using allylic fluorides in the presence
of common Lewis base catalysts. The reactions are rendered enantioselective in
the presence of chiral Lewis base catalysts and produce suitably protected
derivatives of enantioenriched chiral β-amino acids.
M. Lange, F. L. Meyer, O. Nosovska, I. Vilotijevic, Org. Lett., 2023, 25,
9097-9102.
Silyl carbamates undergo allylation using allylic fluorides in the presence
of common Lewis base catalysts. The reactions are rendered enantioselective in
the presence of chiral Lewis base catalysts and produce suitably protected
derivatives of enantioenriched chiral β-amino acids.
M. Lange, F. L. Meyer, O. Nosovska, I. Vilotijevic, Org. Lett., 2023, 25,
9097-9102.
A facile route to ynamides in high yields was achieved through an
iron-catalyzed C-N coupling reaction of amides with alkynyl bromides in the
presence of 20 mol % of N,N′-dimethylethane-1,2-diamine (DMEDA).
B. Yao, Z. Liang, T. Niu, Y. Zhang, J. Org. Chem., 2009,
74, 4630-4633.
A robust transition-metal-free reaction of sulfonamides and (Z)-1,2-dichloroalkenes
or alkynyl chlorides enables the synthesis of internal and terminal ynamides.
The reaction tolerates various functional groups.
X. Zeng, Y. Tu, Z. Zhang, C. You, J. Wu, Z. Ye, J. Zhao, J. Org. Chem., 2019, 84,
4458-4466.
An efficient palladium-catalyzed homocoupling reaction of 2-bromo-1-iodoalkenes
gives 1,3-diynes. Moreover, ynamides can be synthesized in high yields from
2-bromo-1-iodoalkenes and carbamates using nanoparticulate copper(I) oxide as
catalyst.
J. Xue, M.-T. Luo, Y.-L. Wen, M. Ye, L.-X. Liu, Z.-W. Chen, Synthesis, 2014, 46,
3191-3198.
Acid- or base-promoted condensation reactions of carbamates with β-alcoxyacrylates
provide N-monosubstituted
β-Aminoacrylates. Whereas the base-promoted reaction is E-selective, acid catalysis can selectively form
E or Z isomers depending on the solvent.
S. R. Pollack, A. Dion, J. Org. Chem., 2021, 86,
11748-11762.
Acid- or base-promoted condensation reactions of carbamates with β-alcoxyacrylates
provide N-monosubstituted
β-Aminoacrylates. Whereas the base-promoted reaction is E-selective, acid catalysis can selectively form
E or Z isomers depending on the solvent.
S. R. Pollack, A. Dion, J. Org. Chem., 2021, 86,
11748-11762.
Rhodium(II) azavinyl carbenes, which are conveniently generated from
1-sulfonyl-1,2,3-triazoles, undergo a facile, mild, and convergent formal
1,3-insertion into N-H and O-H bonds of primary and secondary amides, various
alcohols, and carboxylic acids to afford a wide range of vicinally
bisfunctionalized (Z)-olefins with perfect regio- and stereoselectivity.
S. Chuprakov, B. T. Worrell, N. Selander, R. K. Sit, V. V. Fokin, J. Am. Chem. Soc., 2014,
136, 195-202.
CeCl3 • 7H2O/NaI supported on
neutral alumina (Al2O3) promotes heteroatom Michael
additions under solvent-free conditions. The CeCl3 • 7H2O/NaI/Al2O3
system works well for hetero-Michael additions of weak nucleophiles such as
imidazoles and carbamates to various acceptors.
G. Bartoli, M. Bartolacci, A. Giuliani, E. Marcantoni, M. Massaccesi, E.
Torregiani, J. Org. Chem., 2005,
70, 169-174.
An efficient palladium-catalyzed asymmetric amination of 2,3-allenyl
phosphates with nitrogen nucleophiles such as amines, hydroxylamines, and
imides can be performed in presence of SEGPHOS or MeOBIPHEP ligand,
affording the corresponding optically active 1-aminated derivatives with
high enantiomeric excess.
Y. Imada, M. Nishida, K. Kutsuwa, S.-I. Murahashi, T. Naota, Org. Lett.,
2005,
7, 5837-5839.