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Synthesis of thiocyanates
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A practical, rapid, and efficient microwave (MW) promoted nucleophilic
substitution of alkyl halides or tosylates with alkali azides, thiocyanates
or sulfinates in aqueous media tolerates various reactive functional groups.
Y. Ju, D. Kumar, R. S. Varma, J. Org. Chem., 2006, 71, 6697-6700.
A novel and highly selective method uses triphenylphosphine,
diethylazodicarboxylate and NH4SCN for the conversion of
alcohols, thiols, carboxylic acids, silyl ethers, and silyl carboxylates to
their corresponding thiocyanates.
N. Iranpoor, H. Firouzabadi, B. Akhlaghinia, R. Azadi, Synthesis, 2004,
92-96.
SO2F2 promotes a one-step synthesis of thiocyanates
through C-O bond cleavage of readily available alcohols with ammonium
thiocyanate as the thiocyanating agent. A borad range of alcohols reacted with
high efficiency in ethyl acetate under mild conditions to afford the
corresponding thiocyanates in very good yields with broad functional group
compatibility.
G. Zhang, L. Xuan, Y. Zhao, C. Ding, Synlett, 2020,
31,
1413-1417.
Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents
for nucleophilic substitution reactions of sulfonate esters derived from primary
and secondary alcohols. The newly developed protocol is very environmentally
attractive because the reactions use stoichiometric amounts of ionic liquids as
sole reagents without additional solvents and activating reagents. Moreover,
these ionic liquids can be readily recycled.
Y. Liu, Y. Xu, S. H. Jung, J. Chae, Synlett, 2012, 23,
2663-2666.
A cross-coupling reaction of arylboronic acids with KSCN salt to yield aryl
thiocyanates is catalyzed by copper acetate in the presence of 4-methylpyridine
serving both as ligand and base under 0.2 MPa of molecular oxygen. Various
arylboronic acids were suitable under the reaction conditions.
N. Sun, H. Zhang, W. Mo, B. Hu, Z. Shen, X. Hu, Synlett, 2013, 24,
1443-1447.
Various aromatic and heteroaromatic compounds have been efficiently thiocyanated
by using a combination of bromodimethylsulfonium bromide (BDMS) and ammonium
thiocyanate.
D. S. Bhalerao, K. G. Agamanchi, Synlett, 2007,
2952-2956.
Iron(III) chloride is an effective Lewis acid for the activation of N-thiocyanatosaccharin
and the subsequent thiocyanation of a wide range of activated arenes. The
procedure was applicable for the thiocyanation of biologically active compounds
such as metaxalone and an estradiol derivative.
L. J. N. Waddell, M. R. Senkrans, A. Sutherland, J. Org. Chem., 2023, 88,
7208-7218.
A stereoselective gold-catalyzed hydrothiocyanation of haloalkynes provided
vinyl thiocyanates in good yields. Furthermore, a sulfur-based gold catalyst
(PPh3AuSCN) has shown a unique reactivity in gold-catalyzed reactions
such as the cyclization of N-propargylic amides.
X. Zeng, B. Chen, Z. Lu, G. B. Hammond, B. Xu,
Org. Lett., 2019, 21, 2772-2776.
Individual β-hydroxy thiocyanates can be synthesized in high yield and with
more than 90% regioselectivity in the presence of phenol-containing macrocyclic
diamides under mild reaction conditions. The method offers high regioselectivity,
simple regeneration/reuse of catalyst through several cycles without a decrease
in activity, and ease of workup of the reaction.
H. Sharghi, M. A. Nasseri, K. Niknam, J. Org. Chem., 2001,
66, 7287-7293.
A simple and efficient FeCl3-mediated method for the α-thiocyanation
of ketones produces α-oxo thiocyanates in very good yields and with high
selectivity under mild conditions. The use of inexpensive and readily available
iron(III) chloride makes this procedure simple, convenient and practical.
J. S. Yadav, B. V. S. Reddy, U. V. S. Reddy, D. N. Chary, Synthesis, 2008,
1283-1287.
A mild and environmentally friendly visible-light-mediated additive-free
decarboxylative functionalization of acrylic acids in the presence of ammonium
thiocyanate, the inexpensive organic dye 9,10-dicyanoanthracene as a
photocatalyst, and dioxygen as both an oxygen source and an oxidant provides a
series of important α-thiocyanate ketones.
Z.-L. Wang, J. Chen, Y.-H. He, Z. Guan, J. Org. Chem., 2021, 86,
3741-3749.
A mild oxidation of selected anions (N3-, SCN-, I-, and Br-) by ceric ammonium
nitrate (CAN) in the presence of substituted cyclopropyl alcohols provides β-functionalized
ketones in short reaction times. This method provides an alternative
pathway to important starting materials and intermediates in organic synthesis.
J. Jiao, L. X. Nguyen, D. R. Patterson, R. A. Flowers II, Org. Lett., 2007,
9, 1323-1326.
Anhydrous FeCl3 oxidizes potassium thiocyanate to the corresponding
radical and promotes subsequent addition to nucleophilic olefins to produce
dithiocyanate derivatives under mild conditions with excellent yields and
chemoselectivities. The use of ferric chloride makes this method simple,
convenient and practical.
J. S. Yadav, B. V. S. Reddy, M. K. Gupta, Synthesis,
2004, 1983-1986.
A 1,2-thiocyanatosulfonation of terminal alkynes with NH4SCN and
sulfonyl hydrazides provides (E)-β-(thiocyanato)vinyl sulfones via a
radical pathway. This metal-free reaction offers mild conditions, readily
available reagents, a broad substrate scope, good functional group compatibility,
and excellent stereoselectivity.
M. Zhang, X. Zeng, Org. Lett., 2021, 23,
3326-3330.