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Synthesis of benzylic amines
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In the presence of 2-amino-2-phenylpropanoate salts as the amine source,
aromatic aldehydes underwent an efficient decarboxylative transamination under
very mild conditions to produce a variety of arylmethylamines in very good
yields.
W. Cai, Y. Yang, J. Ma, J. Cao, X. Ren, B. Zhao, Org. Lett., 2023, 25,
3876-3880.
An efficient, metal and base-free, chemoselective reaction of boronic acids with
cyanamidyl/arylcyanamidyl radicals provides primary aryl-, heteroaryl-, and
alkyl amines at ambient temperature within 1 h. The reaction is mediated by PIFA
and NBS.
N. Chatterjee, M. Arfeen, P. V. Bharatam, A. Goswami, J. Org. Chem.,
2016,
81, 5120-5127.
A highly active Mn(I) pincer catalyst enables an atom-economic and
highly efficient N-alkylation of amines with alcohols utilizing the borrowing
hydrogen methodology. A broad range of anilines and more challenging aliphatic
amines were alkylated with primary and secondary alcohols. The reaction offers
low catalyst loadings and mild reaction conditions.
L. Homberg, A. Roller, K. C. Hultzsch,
Org. Lett., 2019, 21, 3142-3147.
Well-defined Co(II) complexes stabilized by a PCP ligand catalyze efficient
alkylations of aromatic amines by primary alcohols into mono-N-alkylated
amines in very good yields. The inexpensive, earth-abundant nonprecious metal
catalysts make this acceptorless alcohol dehydrogenation concept environmentally
benign.
M. Mastalir, G. Tomsu, E. Pittenauer, G. Allmaier, K. Kirchner, Org. Lett.,
2016, 18, 3462-3465.
Commercially available [(PPh3)2NiCl2] is an
efficient catalyst for the mono-N-alkylation of (hetero)aromatic amines,
employing alcohols to deliver diverse secondary amines in excellent yields via
the borrowing hydrogen strategy. The catalyst system can also be used for
accessing various quinoline derivatives following the acceptorless
dehydrogenation pathway.
S. N. R. Donthireddy, V. K. Pandey, A. Rit, J. Org. Chem., 2021, 86,
6994-7001.
Low loadings of an air-stable and easy to prepare Ru complex bearing a
tridentate redox-active azo-aromatic pincer ligand catalyze N-alkylation
of amines with C3-C10 alcohols. A wide array of N-methylated, N-ethylated,
and N-alkylated amines were prepared in good yields with wide functional
group tolerance.
A. K. Guin, S. Pal, S. Chakraborty, S. Chakraborty, N. D. Paul, J. Org. Chem., 2023, 88,
5944-5961.
Imines and secondary amines were synthesized selectively by a Pd-catalyzed
one-pot reaction of benzyl alcohols with primary amines. The reactions did not
require any additives and were effective for a wide range of alcohols and
amines.
M. S. Kwon, S. Kim, S. Park, W. Bosco, R. K. Chidrala, J. Park, J. Org. Chem., 2009,
74, 2877-2879.
The addition of 4 Å molecular sieves enables an efficient cobalt(II)-catalyzed
N-alkylation of both aromatic and aliphatic amines with alcohols with high
chemoselectivity (amines vs imines). A hydrogen-borrowing mechanism is
responsible for the tandem acceptorless dehydrogenation/condensation/hydrogenation
process.
G. Zhang, Z. Yin, S. Zheng, Org. Lett., 2016, 18,
300-303.
A Chan-Lam coupling reaction of benzylic and allylic boronic esters
with primary and secondary anilines provides valuable alkyl amine products. Both
secondary and tertiary boronic esters can be used as coupling partners, with
mono-alkylation of the aniline occurring selectively.
J. D. Grayson, F. M. Dennis, C. C. Robertson, B. M. Partridge, J. Org. Chem., 2021, 86,
9883-9897.
A catalytic system generated in situ from a tetranuclear Ru-H complex with a
catechol ligand enables a direct deaminative coupling of two primary amines to
form secondary amines. The analogous coupling of aniline with primary amines
formed aryl-substituted secondary amines.
P. T. K. Arachchige, H. Lee, C. S. Yi, J. Org. Chem., 2018, 83,
4932-4947.
A monobenzylation of aromatic amines with benzylic alcohols in good yields
proceeds under MW conditions in the presence of SmI2 as a catalyst
with the generation of water as the sole byproduct. This reaction offers a broad
substrate scope and good functional-group tolerance.
J. Gour, S. Gatadi, S. Malasala, M. V. Yaddanpudi, S. Nanduri, J. Org. Chem., 2019, 84,
7488-7494.
SPINOL-derived borophosphates catalyze an asymmetric reductive amination of
ketones with pinacolborane to provide a series of chiral amine derivatives
bearing multiple functional groups in very good yields and enantioselectivities
under mild reaction conditions.
Z. Wu, H. He, M. Chen, L. Zhu, W. Zheng, Y. Cao, J. C. Antilla, Org. Lett., 2022, 24,
9436-9441.
The use of 1,2-benzisoxazole as a practical electrophilic primary amine source
enables a mild and general copper-hydride-catalyzed hydroamination of alkenes and alkynes
to form primary amines. This method provides access to a broad
range of chiral α-branched primary amines and linear primary amines.
S. Guo, J. C. Yang, S. L. Buchwald, J. Am. Chem. Soc.,
2018,
140, 15976-15984.
A protocol for the dehydrative amination of alcohols in water using a
water-soluble calix[4]resorcinarene sulfonic acid as a reusable multifunctional
catalyst allows an environmentally benign synthesis of benzylic and allylic
amines. The aqueous phase containing the catalyst can be readily recycled.
S. Shirakawa, S. Shimizu, Synlett, 2008,
1539-1542.
A catalytic amount of manganese dioxide and solvent-free conditions under air
enabled a practical and efficient N-alkylation method for a variety of
sulfonamides and amines using alcohols as green alkylating reagents.
X. Yu, C. Liu, L. Jiang, Q. Xu, Org. Lett., 2011,
13, 6184-6187.
Halogen bonding induces an intermolecular Csp3-H amination and
even enables a hydrogen atom transfer relay strategy to access privileged
pyrrolidine structures directly from alkanes. Mechanistic studies support the
presence of multiple halogen bond interactions.
F. Wu, J. P. Ariyarathna, N. Kaur, N.-E. Alom, M. L. Kennell, O. H. Bassiouni,
W. Li,
Org. Lett., 2020, 22, 2135-2140.
A base-catalyzed/promoted transition-metal-free direct alkylation of amines with
either aromatic or aliphatic alcohols provides the desired amines in good yields.
Q.-Q. Li, Z.-F. Xiao, C.-Z. Yao, H.-X. Zheng, Y.-B. Kang, Org. Lett.,
2015,
17, 5328-5331.
A well-defined Zn(II)-complex catalyzes a sustainable and eco-friendly N-alkylation
of various amines by alcohols in very good yields. The method shows wide
functional group tolerance and produces the precursors in high yields for the
marketed drugs tripelennamine and thonzonium bromide in gram-scale reactions.
S. Chakraborty, R. Mondal, S. Pal, A. J. Guin, L. Roy, N. D. Paul, J. Org. Chem., 2023, 88,
771-787.
A highly enantio- and regioselective copper-catalyzed hydroamination reaction of
alkenes with hydroxylamine esters in the presence of diethoxymethylsilane
enables the conversion of a wide variety of substituted styrenes, including
trans-, cis-, and β,β-disubstituted styrenes, to yield α-branched
amines. In addition, aliphatic alkenes gave exclusively the anti-Markovnikov
hydroamination products.
S. Zhu, N. Niljianskul, S. L. Buchwald, J. Am. Chem. Soc., 2013,
135, 15746-15749.
A CuH-catalyzed hydroamination of alkenes using an amine transfer reagent and a
silane provides chiral amines with high efficiency and stereoselectivity.
However, the current technology has been limited to dialkylamine transfer
reagents (R2NOBz). A modified type of monoalkylamine transfer enabled
the synthesis of chiral secondary amines, including those derived from amino
acid esters, carbohydrates, and steroids.
D. Niu, S. L. Buchwald, J. Am. Chem. Soc., 2015,
137, 9716-9721.
An efficient, palladium-catalyzed hydroamination of vinylarenes using aromatic
amines provides sec-phenethylamine products in the presence of an acid
cocatalyst.
M. Kawatsura, J. F. Hartwig, J. Am. Chem. Soc., 2000,
122, 9546-9547.
Benzylic hydrocarbons are selectively converted to the corresponding
sulfonamides by the [Cu(CH3CN)4]PF6-catalyzed reaction with anhydrous
TolSO2NNaCl (chloramine-T). Under the same conditions, representative ethers
and olefins are
also amidated.
R. Bhuyan, K. M. Nicholas, Org. Lett., 2007,
9, 3957-3959.
A palladium complex generated in situ from [Pd(η3-C3H5)(cod)]BF4
and DPPF is a good catalyst for benzylations of malonates with a wide range
of benzyl methyl carbonates. The DPEphos ligand is superior to DPPF in the
case of palladium-catalyzed benzylic amination of benzylic esters.
R. Kuwano, Y. Kondo, Y. Matuyama, J. Am. Chem. Soc.,
2003,
125, 12104-12105.
A Mannich-like zinc-mediated three-component reaction of aromatic halides,
amines, and paraformaldehyde allows the straightforward synthesis of a range of
functionalized tertiary benzylamines. This procedure involves the in situ
formation of arylzinc reagents.
E. Le Gall, A. Decompte, T. Martens, M. Troupel, Synthesis, 2010,
249-254.
Treatment of ketones with
ammonia in ethanol and titanium(IV) isopropoxide, followed by in situ reduction
with sodium borohydride allows a highly chemoselective reductive
mono-alkylation of ammonia. A simple workup afforded primary amines in good to
excellent yields. Reductive alkylation of ammonia with aldehydes afforded the corresponding symmetrical secondary amines selectively.
B. Miriyala, S. Bhattacharyya, J. S. Williamson, Tetrahedron, 2004,
60, 1463-1471.
The use of an oxazaborolidine-BH3 complex enables a simple and
efficient copper-catalyzed selective transfer hydrogenation of nitriles to
primary amine-boranes and secondary amines in good yields. The selectivity
control was achieved under mild conditions by switching the solvent and the
copper catalysts.
H. Song, Y. Xiao, Z. Zhang, W. Xiong, R. Wang, L. Guo, T. Zhou, J. Org. Chem., 2022, 87,
790-800.
A metal bis(trimethylsilyl)amide/Cs2CO3 co-catalyzed
benzylation of in situ generated N-(trimethylsilyl) aldimines with toluene
derivatives provides a diverse array of bioactive 1,2-diarylethylamines with excellent efficiency and broad
functional group tolerance. The catalyst exhibits high
chemoselectivity for deprotonation of toluenes at the benzylic position.
G. Liu, P. J. Walsh, J. Mao,
Org. Lett., 2019, 21, 8514-8518.
A simple Re2O7-catalyzed direct dehydrative coupling
between π-activated alcohols with electron-deficient amines has been
achieved under mild and open flask conditions. The protocol alows the conversion
of allylic, benzylic, and propargylic alcohols. The mechanistic proof for the SN1-type
process has also been provided.
B. G. Das, R. Nallagonda, P. Ghorai, J. Org. Chem., 2012,
77, 5577-5583.
The synthesis of free α-chiral amines by a one-pot multicomponent procedure
involves the formation of N-diphenylphosphinoylimines from
commercially available starting materials and the subsequent
enantioselective addition of diakylzinc reagents using an air-stable
precatalyst complex.
. Cote, A. B. Charette, J. Org. Chem.,
2005,
70, 10864-10867.
Nickel nanoparticles catalyse the reductive amination of aldehydes by transfer
hydrogenation with isopropanol at 76°C.
F. Alonso, P. Riente, M. Yus, Synlett, 2008, 1289-1292.
Manganese dioxide is employed as an in situ oxidant for the one-pot conversion
of alcohols into imines. In combination with polymer-supported cyanoborohydride
(PSCBH), a one-pot oxidation-imine formation-reduction sequence enables alcohols
to be converted directly into both secondary and tertiary amines.
L. Blackburn, R. J. K. Taylor, Org.
Lett., 2001, 3, 1637-1639.
Treatment of methylarenes with 1,3-dibromo-5,5-dimethylhydantoin or N-bromosuccinimide
and a catalytic amount of 2,2′-azobis(isobutyronitrile) followed by a reaction
with a nucleophile, such as benzoic acid, p-toluenethiol, sodium p-toluenesulfinate,
aqueous dimethylamine, or succinimide, provides the corresponding benzylated
products in good yields.
H. Shimojo, K. Moriyama, H. Togo, Synthesis, 2015, 47,
1280-1290.
A Lewis acid palladium-catalyzed reaction of amides, aryl aldehydes, and
arylboronic acids enables a practical and general synthesis of α-substituted
amides from simple, readily available building blocks.
T. Beisel, G. Manolikakes, Org. Lett., 2013,
15, 6046-6049.
A palladium-catalyzed, enantioselective three-component reaction of
sulfonamides, aldehydes, and arylboronic acids generates a wide array of
α-arylamines with high yields and enantioselectivities. Notably, this process
tolerates air and moisture and provides an operationally simple approach
for the synthesis of chiral α-arylamines.
T. Beisel, G. Manolikakes, Org. Lett.,
2015,
17, 3162-3165.
N-(Diphenylmethylene)-1,1,1-trifluoromethanesulfonamide is a
bench-stable and readily accessible carboamination reagent, that enables a
facile and versatile trifluoromethylimination of alkenes under metal-free
photocatalytic conditions. The mild reaction conditions and good functional
group compatibility render this protocol highly valuable for the
difunctionalization of olefins.
Y. Zheng, Z. Liao, Z. Xie, H. Chen, K. Chen, H. Xiang, H. Yang, Org. Lett., 2023, 25,
2129-2133.
Aromatic aldehydes can be converted to α-amino anion equivalents via amination
with 2,2-diphenylglycine and subsequent decarboxylation. These in situ generated
α-imino anions are highly reactive for Pd-catalyzed allylation to give
homoallylic amines in high yields with excellent regioselectivity.
L. Ding, J. Chen, Y. Hu, J. Xu, X. Gong, D. Xu, B. Zhao, H. Li, Org. Lett., 2014,
16, 720-723.
A one-pot catalyst-free chemoselective synthesis of N-benzyl
propargylamines with good functional group compatibility involves in situ
formation of an active amine through Petasis reaction of primary amines,
formaldehyde solution, and boronic acids, which reacts in a decarboxylative
coupling reaction with propiolic acids to give products in high yields.
H. Feng, H. Jia, Z. Sun, J. Org. Chem.,
2014,
79, 11812-11818.
A wide range of chiral propargylamines can be prepared in a one-pot
three-component reaction between an alkyne, an aldehyde and a secondary
amine at room temperature in the presence of CuBr and (R)-quinap in
good yield and good enantioselectivity.
N. Gommermann, C. Koradin, K. Polborn, P. Knochel, Angew. Chem., 2003,
115, 5941-5944.
The regioselective opening of Bn2N-α-methylserine-β-lactone
with organocuprates gave enantiopure α-methyl amino acids in excellent yields.
N. D. Smith, A. M. Wohlrab, M. Goodman, Org. Lett., 2005,
7, 255-258.
A Cu-catalyzed regioselective and stereospecific aminoboration of styrenes with
bis(pinacolato)diboron and O-benzoyl-N,N-dialkylhydroxylamines
delivers β-aminoalkylboranes in good yields. The Cu catalysis enables
introduction of both amine and boron moieties to C-C double bonds simultaneously
in a syn fashion. Moreover, the use of a chiral biphosphine ligand, (S,S)-Me-Duphos,
provides optically active β-aminoalkylboranes.
N. Matsuda, K. Hirano, T. Satoh, M. Miura, J. Am. Chem. Soc., 2013,
135, 4934-4937.
An organo-photocatalytic sulfonylimination of alkenes using readily available
N-sulfonyl ketimines as bifunctional reagent enables a direct and
atom-economic synthesis of valuable β-amino sulfone derivatives as a single
regioisomer. A formal insertion of alkenes into cyclic sulfonyl imines affords
ring expansion products.
L. Wang, Y. Yu, L. Deng, K. Du, Org. Lett., 2023, 25,
2349-2354.