Categories: C=N Bond Formation >
Synthesis of imines
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A mild three-component reaction of aromatic aldehydes, alkyl bromides, and
aqueous ammonia as the nitrogen source gives imines in very good yields. The
reaction conditions are compatible with a range of functional groups. The
reaction of aldehydes and aqueous ammonia with epoxides leads to imines bearing
a vicinal hydroxyl group regioselectively.
J.-M. Huang, J.-F. Zhang, Y. Dong, W. Gong, J. Org. Chem., 2011,
76, 3511-3514.
Neat non-volatile amines react efficiently with various aromatic aldehydes
in the absence of any catalyst or solvent, to give imines after a reaction
time of eight minutes under microwave irradiation. 1,3-dimethylurea
dispersed on montmorillonite K10 is used as an methylamine precursor.
L. Paquin, J. Hamelin, F. Texier-Boullet, Synthesis, 2006, 1652-1656.
Pyrrolidine as an organocatalyst enables a general and efficient biomimetic
method for the synthesis of aldimines from aldehydes and compounds bearing an
amino group. This nucleophilic catalysis proceeds via iminium activation with
outstanding yields in the absence of acids and metals under simple conditions.
The method has been applied to the synthesis of N-sulfinyl, N-sulfonyl
imines, N-phosphinoyl, N-alkyl, and N-aryl imines.
S. Morales, F. G. Guijarro, J. L. G. Ruano, M. B. Cid, J. Am. Chem. Soc., 2014,
136, 1082-1089.
The reaction of an arylaldehyde and a sulfonylisocyanate in a solvent or in neat
form under catalyst- and additive-free conditions gives the desired N-sulfonylimine
with the release of carbon dioxide. The method offers unique clean efficiency,
convenience, and scalability, although it was reported to fail half a century
ago.
D. Huang, X. Wang, X. Wang, W. Chen, X. Wang, Y. Hu, Org. Lett., 2016, 18,
604-607.
Tris(2,2,2-trifluoroethyl)borate [B(OCH2CF3)3]
is a mild and general reagent for condensation of amides or amines with carbonyl
compounds providing N-Sulfinyl, N-toluenesulfonyl, N-(dimethylamino)sulfamoyl,
N-diphenylphosphinoyl, N-(α-methylbenzyl), and N-(4-methoxyphenyl)
aldimines at room temperature. The reactions are operationally simple, and the
products are obtained without special workup or isolation procedures.
J. T. Reeves, M. D. Visco, M. A. Marsini, N. Grinberg, C. A. Busacca, A. E.
Mattson, C. H. Senanayake, Org. Lett.,
2015,
17, 2442-2445.
The use of low loadings of a silver NHC catalysts enables a mild, selective
oxidation of alcohols to aldehydes or carboxylic acids in the presence of BnMe3NOH
or KOH under dry air in excellent yield. The catalytic system can also be used
for a one-pot synthesis of imines in excellent yield.
L. Han, P. Xing, B. Jiang, Org. Lett., 2014,
16, 3428-3431.
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.
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.
A modular aerobic oxidation of amines to imines has been achieved using an
ortho-naphthoquinone (o-NQ) catalyst. Whereas the cooperative
catalyst system of o-NQ and Cu(OAc)2 provided homocoupled
imines from benzylamines, the presence of TFA helped the formation of
cross-coupled imines in excellent yields. The oxidation of secondary amines to
imines or ketimines is facilitated with the help of Ag2CO3
as cocatalyst.
Y. Goriya, H. Y. Kim, K. Oh, Org. Lett.,
2016, 18, 5174-5177.
Iron-catalyzed aerobic oxidative reactions of primary amines, secondary amines,
benzylamines with anilines, and alcohols with amines in the presence of air as
the economic and safe oxidant, provide several direct, practical, and greener
approaches for the preparation of useful imines.
E. Zhang, H. Tian, S. Xu, X. Yu, Q. Xu, Org. Lett., 2013,
15, 2704-2707.
A base-mediated protocol enables the synthesis of imines and amines from N-phenylureas
and alcohols in good yields under air. This protocol is as an efficient
alternative to conventional methods for the synthesis of imines and amines.
D. K. T. Yadav, B. M. Bhanage,
Synlett, 2014, 25, 1611-1615.
An intermolecular reductive Schiff base formation from nitroarenes and
benzaldehydes to yield diarylimines is carried out in the presence of iron
powder and dilute acid. This process tolerates various functional groups and
often proceeds quantitatively with no need for purification.
A. L. Korich, T. S. Hughes, Synlett, 2007,
2602-2604.
The use of photosensitive C70 for the catalytic oxidation of
benzylamines to the corresponding imines enables faster reaction rates, lower
catalyst loadings, and clean reactions with simple workup without chromatography,
compared to C60 or other commonly used photosensitizers such as
tetraphenylporphyrin (TPP). Singlet oxygen (1O2) and the
superoxide radical anion (O2•–) act as important reactive
species in this oxidation.
R. Kumar, E. H. Gleißner, E. G. V. Tiu, Y. Yamakoshi, Org. Lett., 2016, 18, 184-187.
By employing Pd(OAc)2 and (t-Bu)2PNP(i-BuNCH2CH2)3N
as ligand, a broad range of aryl bromides and chlorides possessing
base-sensitive substituents provide coupling products with bulky aryl amines in
good to excellent yields. An efficient coupling of vinyl bromides with a variety
of amines produces imines and enamines at room temperature.
Ch. V. Reddy, J. V. Kingston, J. G. Verkade, J. Org. Chem., 2008,
73, 3047-3062.
A Michael addition of amines and hydrazines to nitrostyrenes provides N-alkyl/aryl
substituted benzyl imines and N-methyl/phenyl substituted benzyl
hydrazones via a retro-aza-Henry-type process under mild, noncatalytic
conditions. The method can be used for the synthesis of biologically important
N-methyl pyrazoles in a one-pot manner, simple starting with the
corresponding nitrostyrenes and the methylhydrazine.
M. G. Kallitsakis, P. D. Tancini, M. Dixit, G. Mpourmpakis, I. N. Lykakis, J. Org. Chem.,
2018, 83, 1176-1184.
A novel Au(I)-precatalyst is applied to intermolecular alkyne hydroamination.
DFT calculations revealed the cyclopropenium counterion of this
Au(I)-precatalyst imparts stability through H-bonding and other noncovalent
interactions.
R. Mir, T. Dudding, J. Org. Chem.,
2016,
81, 2675-2679.
Readily available and stable titanocene-alkyne complexes can be used for the
hydroamination of internal and terminal alkynes. The reactions of terminal alkynes with aliphatic amines proceed highly
selectively to give the corresponding primary anti-Markovnikov functionalized
imines in good to excellent yields.
A. Tillack, I. G. Castro, C. G. Hartung, M. Beller, Angew. Chem. Int. Ed.,
2002, 41, 2541-2543.
Use of the heterogeneous catalyst amberlist-15 A enables an efficient synthesis
of N-(tert-butylsulfinyl)imines under microwave irradiation. Amberlist-15
is convenient to handle, inexpensive, safe to use and quickly separable from the
reaction mixture. This method offers a number of advantages including
operational simplicity, high yield of products, and broad substrate scope.
C. Sanaboina, S. Jana, L. Eppakayala,
Synlett, 2014, 25, 1006-1008.
Microwave-promoted condensation of carbonyl compounds with (R)-2-methylpropane-2-sulfinamide
under solvent-free conditions in the presence of Ti(OEt)4 enables a
simple, environmentally friendly synthesis of optically pure N-(tert-butylsulfinyl)imines.
Sulfinyl aldimines can be prepared with excellent yields and purities in only 10
min, whereas the reaction time for the preparation of ketimines has been
extended to 1 h.
J. F. Collados, E. Toledano, D. Guijarro, M. Yus, J. Org. Chem., 2012,
77, 5744-5750.
A number of new reactions of IBX with heteroatom-containing substrates were
discovered and their utility was demonstrated. IBX was used for the generation
of imines from secondary amines in notably high yields, for the oxidative
aromatization of nitrogen heterocycles and for the cleavage of dithianes.
K. C. Nicolaou, C. J. N. Mathison, T. Montagnon, Angew.
Chem., 2003, 115, 4211-4216.
[RuCl2(CO)3]2/dppp is a highly effective
catalyst system for the intramolecular oxidative amination of various
aminoalkenes in presence of K2CO3 and allyl acetate in
N-methylpiperidine to give the corresponding cyclic imines and
indoles in excellent yields.
T. Kondo, T. Okada, T.-A. Mitsudo, J. Am. Chem. Soc., 2002, 124,
186-187.
A transition-metal-free oxidative C-C bond cleavage process for a broad range of
ester and dicarbonyl compounds involves carbanion addition to nitrosobenzene and
proceeds via fragmentation of a previously unobserved oxazetidin-4-one
heterocycle.
J. N. Payette, H. Yamamoto, J. Am. Chem. Soc., 2008,
130, 12276-12278.
The reaction of aldehydes, amines, and TMSCN in the presence of 2-iodoxybenzoic
acid (IBX) and tetrabutylammonium bromide (TBAB) afforded α-iminonitriles in
good to excellent yields under mild conditions. The presence of TBAB is
essential for this transformation.
P. Fontaine, A. Chiaroni, G. Masson, J. Zhu, Org. Lett., 2008,
10, 1509-1512.
A highly regioselective hydroamination of unsymmetrical electron-poor and
electron-rich alkynes with anilines is catalyzed by Au(I) under mild conditions.
In addition, applications toward indole syntheses are presented including an
example of a one-pot synthesis from a nonfunctionalized aniline.
S. Kramer, K. Dooleweerdt, A. T. Lindhardt, M. Rottländer, T. Skrydstrup, Org. Lett., 2009,
11, 4208-4211.
A high-yielding, asymmetric synthesis of novel 4-formyl-1-(2- and
3-haloalkyl)azetidin-2-ones was developed as valuable starting materials for the
synthesis of different enantiomerically enriched bicyclic azetidin-2-ones, such
as piperazine, morpholine, and 1,4-diazepane annulated β-lactam derivatives.
W. Van Brabandt, M. Vanwalleghem, M. D'hooghe, N. De Kimpe, J. Org. Chem., 2006, 71, 7083-7086.