Potassium Thiocyanate (KSCN)

SPOTLIGHT 2035

SYNLETT Potassium Thiocyanate (KSCN): Spotlight 284 A Versatile Reagent Compiled by Soheil Sayyahi This feature focuses on a re- Soheil Sayyahi was born in Ahwaz, Iran in 1975. He received his agent chosen by a postgradu- Bachelor and M.Sc. degrees from Shahid Chamran University of ate, highlighting the uses and Ahwaz, where he is currently carrying out his Ph.D. under the su- preparation of the reagent in pervision of Prof. Kiasat and Prof. Badri. His area of research in- current research cludes the application of polymer-supported reagents and catalysts in organic synthesis. Chemistry Department, College of Science, Chamran University, Ahvaz 61357-4-3169, Iran E-mail: [email protected]

Introduction nyl thiocyanates and isothiocyanates from alkenes.3 Vari- ous tosyl and bromo derivatives of Cbz-, Boc-, and Fmoc- Potassium thiocyanate (KSCN) is a white odorless, crys- protected threonine methyl esters have been subjected to talline powder, slightly hydroscopic, and commercially nucleophilic substitution with potassium thiocyanate in available reagent. It is readily soluble in water and stable acetonitrile for the synthesis of allo- and threo-3,3¢-dime- under normal temperature and pressure (mp: 173 °C, d = thylcystine derivatives.4 This reagent is supported on sili- 1.89 g/cm3). Since sulfur-containing groups serve as an ca gel and applied for thiocyanation of b-dicarbonyl important auxiliary function in synthetic sequences,1 po- compounds and the synthesis of 2-aminothiazoles.5 Re- tassium thiocyanate is widely used as a transfer reagent cently, potassium thiocyanate is used for the conversion for sulfur in various organic transformations.2 The hyper- of alkyl halides into alkyl thiocyanate in water under valent iodine(III) in combination with potassium thio- phase-transfer catalysis.6 It is also employed for the cyanate and diphenyl diselenide promoted a synthesis of 1-aroyl-3-(substituted-2-benzothiazolyl)thio- multicomponent reaction for the synthesis of phenylsele- ureas with antibacterial properties.7

Abstracts

8 S (A) Das et al. reported an efficient and catalyst-free procedure for O

the synthesis of thiiranes from oxiranes by treatment with KSCN KSCN, PEG

using PEG as a reaction medium at room temperature. r.t., 45 min

89–95%

LiClO

(B) In the presence of a catalytic amount of LiClO , oxiranes are S 4 4

RO KSCN converted into the corresponding thiiranes by potassium thiocyanate +

in nonaqueous condition.9 MeCN, r.t. 72–95%

10a

2 R S

2 (C) Aoyama et al. introduced a supported reagent system, KSCN/ 1 R R

, BnNH OAc, Al O

SiO2 and BnNH3OAc/Al2O3, that has been employed in a one-pot KSCN, SiO

2 3 2 3

N N Ph

synthesis of N-allylthioureas. Also, various a-halo ketones and allyl- Br

C H , 80 °C, 6 h

6 6

3 N R ic bromides were converted into 2-aminothiazoles and -allylthio- R ureas from commercially available materials in one pot by using the

10b This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

supported reagents. O

R N

KSCN, SiO , R NH OAc, Al O X

1 2 3 2 3

3 R NHR

C H , 80 °C, 6 h

6 6

2 2 R R

SYNLETT 2009, No. 12, pp 2035–2036 xx.xx.2009 Advanced online publication: 03.07.2009 DOI: 10.1055/s-0029-1217441; Art ID: V29109ST © Georg Thieme Verlag Stuttgart · New York 2036 SPOTLIGHT

(D) Rao et al. reported a mild and efficient method for the regio- Ts

SCN

O selective ring opening of aziridines with KSCN in the presence of β-CD, H

b-CD as catalyst and water at room temperature with excellent 2

KSCN, r.t.

yields ranging from 78 to 90%. NHTs

R = H, 4-Cl, 4-Br, 4-OMe, 4-Me, 4-COMe

NHTs

O β-CD, H

2 NTs

( )

( ) KSCN, r.t.

n SCN n = 0,1

(E) Recently, a practical synthesis of 1,3-disubstituted imidazole-2- S

thiones via a microwave-promoted reaction of imidazolium salts R

KSCN

2 N

R N

with potassium thiocyanate or potassium thioacetate under solvent- + N

12 –

MW, 50–200 W, 5–15 min

free conditions has been developed. X

(F) Ring-opening reactions of various N-tosylaziridines with KSCN Ts

TsNH H

proceeded in a silica–water reaction medium in good yield with N

R R H 1

silica gel 60 (1.0 g)

complete regioselectivity. The system is applicable to a ring expan- R + KSCN

2 3

O, 80 °C, 24 h H

2 R R sion of an aziridine with potassium thiocyanate leading to a thiazo- 2 R CN

lidine derivative.13 (2 equiv)

C H 6 13

HNTs

silica gel 60 (0.5 g)

S + KSCN

H O, 80 °C, 24 h

H C (2 equiv) 13 6

H C 13 6

(G) The microwave-assisted nucleophilic substitution of potassium

KSCN

RSCN thiocyanate with different halides or tosylates in water has been de- RX

O, MW H

veloped and proved very successful with the formation of alkylthio- 2

78–95% cyanates in good to excellent yields. Noteworthy, no significant X = Br, Cl, I, OTs rearrangement to isothiocyanates was observed.14

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