Potassium selenocyanate, reaction with

Amino-A.-selenazoline and its 5-methyl derivative have previously been obtained by Baringer (61) starting from 2-bromoethylamine hydrobromide and l-amino-2-bromopropane hydrobromide, respectively, by reaction with potassium selenocyanate. 

A related ring closure is also successful in the thiazole series. Treatment of a /3-amino-a,/3-unsaturated ketone with thiocyanogen gave the intermediate thiocyano compound (323) which underwent ring closure to the 2-iminothiazoline derivative (324) (83MI40300). Related reactions are described in Chapter 4.19, and for those involving potassium selenocyanate see Chapter 4.20. 

Diazotization of 3-amino-2-acetylselenophene (105) and reaction with potassium selenocyanide yields the selenocyanate (106) ring closure with ammonia gives the fused system 107 which was O-methylated with dimethyl-sulfate.135... 

Amino-substituted selenophenes are in general unstable compounds, and are conveniently isolated as IV-acetyl or iV-formyl derivatives. An ortho situated electron-attracting substituent such as acetyl, formyl or nitro renders the amino compounds stable. Derivatives of this type can be diazolized and the resulting diazonium salts converted into azides (by reaction with azide ion) (75CR(C)(281)317) and selenocyanates (by reaction with selenocyanide ion) (79BSF(2)237). 3-Acetamidoselenophene can be thiocyanated or selenocyanated in the 2-position by treatment with bromine and potassium thiocyanate or potassium selenocyanate, respectively (78TL1797). 

The selenocyano-group may be introduced conveniently into the benzene nucleus by the aid of the diazo-reaction, e.g. diazotised aniline reacts with potassium selenocyanate to yield phenyl selenocyanate ... 

Aminoanthraquinone, 2 2 kilograms, in concentrated sulphuric acid, is diazotised with nitrosylsulphuric acid. The addition of ice precipitates the diazosulphate, which is removed, dissolved in water and treated with 1 5 kilograms of potassium selenocyanate. The red diazoseleno-cyanate separates out and some nitrogen is evolved. The reaction is completed by warming, whereby an orange precipitate of selenocyanoanthraquinone is obtained. This crystallises from nitrobenzene as yellowish-red needles, M.pt. 249° C. 

Amino-3-methyl- or 5-amino-3-phenyl-l,2,4-selenadiazoles (165) are prepared by reaction of potassium selenocyanate with N-haloamidines (Scheme 68) (63CB1289). 

A similar exchange reaction produced the 1 1 complexes of phenyl tellurium thiocyanate with ethylenethiourea1, when the phenyl tellurium chloride complex was treated with potassium thiocyanate in aqueous methanol. However, the phenyl tellurium chloride -selenourea adduct and potassium selenocyanate yielded bis[phenyIteUuro] selenium3. Phosphane selenides also coordinate to phenyl tellurium halides3. 

Reactions leading to the formation of alkenic or a,/3-unsaturated bonds are very important in synthesis. This type of functionality is synthetically versatile, and of wide utility in the carbohydrate field. The use of sulfur reagents for conversion of sugar epoxides on vicinal disulfonates into al-kenes is well established97a 97b, and subsequent work with selenium reagents provided essentially comparable results. Thus, treatment of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside (219) with potassium selenocyanate in aqueous 2-methoxymethanol afforded methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-ery/firo-hex-2-enopyranoside (220).27 Similarly, treatment of 5,6-anhydro-l,2-0-isopropylidene-a-D-glucofuranose (221) with potassium selenocyanate in methanol at room temperature... 

A striking difference to the reactions with cyanate and thiocyanate [Eq. (95)] has been found with potassium selenocyanate. Elemental selenium is precipitated and cyanide ion is the reactive species in accordance with Eq. (86) (237). 

Benzoselenazole-2-thione 63 is obtained by a four-step procedure starting from o-nitroaniline <2002J(P1)1568, 2001CC1336>. Reaction of potassium selenocyanate with the diazonium salt yields o-nitrophenyl selenocyanate. Treatment of the o-nitrophenyl selenocyanate with sodium in ethanol affords bis(o-nitrophenyl) diselenide. The m situ reduction of this with sodium hydrosulfide gives an intermediate o-aminobenzeneselenoate, which cyclizes with carbon disulfide in basic medium, work-up giving 3/7-benzoselenazole-2-thione 63 (Scheme 22). 

The treatment of simple and fused oxaziridines with sulfur-containing nucleophiles such as thiourea, potassium thiocyanate, potassium ethyl-xanthate, potassium selenocyanate, and triphenyl-phosphine sulfide resulted in the formation of the related imines, most probably—in analogy to the results of the treatment of oxiranes with the same reagents—via the corresponding thiaziridine intermediate. The proposed reaction mechanism is given in Scheme 8 <73AJC2159>. 

The first derivative of this ring system, 2-imino-2,3.5.6-tetrahydro-l,3-selenazine (216), was obtained through the reaction of l-bromo-3-amino-propane with potassium selenocyanate. [Eq. (51)]. 

With other halides, the reaction is conveniently performed by treatment of the alkylthdlium compound with the appropriate copper(I) halide. The product yield is increased by the addition of potassium halide.jhe thallium moiety can also be replaced by other groups, similarly to the arylthallium compounds. The cyano group is introduced by reaction with copper(I) cyanide.lSi the thiocyano group by reaction with potassium and/or copper thiocyanate>5i.i52 and the selenocyano group by treatment with potassium selenocyanate. 

Potassium selenocyanate in acetic anhydride reacts with epoxides to give 2-acetylamino-l,3-oxaselenole derivatives <93JCS(P2)35l>. Low yields of 1,3-oxaselenoles are obtained in the reaction of selenium with ethyne in aqueous base <89ZOR2283). 

When diallyl ether (40) is reacted with potassium selenocyanate, copper(II) chloride, and methanol a mixture of 3,5-bis(methoxymethyl)-1,4-oxaselenane (41) and 3-methoxymethyl-6-methyl-l,4-oxaselenepane (42) is formed. The amount of the selenane increases with reaction time and the ratio of products is also affected by variations in temperature. These facts suggest that an equilibrium exists, linking the products through an intermediate episelenonium cation (43) (Scheme 16) <79JCS(P1)1206>. 

A cyclic sulfate 278 treated with potassium selenocyanate gave the expected selenirane 282, which underwent the elimination of a selenium atom, giving rise to alkene 283 [95JCS(CC)461] (Scheme 71). Interestingly, the reaction of di-O-isopropylidine cyclic sulfate 284 with sodium thioacetate did not yield the corresponding episulfide 285. However, when sodium sulfide was used as a nucleophile in boiling methanol, a 42% yield of episulfide 285 was obtained [Eq. (48)] [94JCS(CC)461]. 

Other Systems.—An oxaselenepan (195) is formed as the primary product by intramolecular oxyselenation in the reaction of diallyl ether with potassium selenocyanate in methanol, in the presence of copper(ii) chloride.A range of... 

The benzo-l,2-selenazine (benzisoselenazine) ring system 144 can be prepared by copper(l)-promoted reaction of amine 143 with potassium selenocyanate in the presence of triethylamine (Equation 37) <2000JOC8152>. The ring closure also affords 3,3-dimethylindoline as a by-product, but a twofold excess of selenocyanate and acetonitrile as a solvent led to optimum formation of the desired selenazine. 

The l,4-selenazin-3-one 168 was prepared as an analog of the cardiotonic drug bemoradan (where Se = 0) <1992JME172>. This ring system can be prepared in a series of reactions by the treatment of the amine 165 with bromine-potassium selenocyanate, followed by sodium sulfide (Scheme 46). The resulting aminoselenol 166 can be cyclized to the selenazinone 167 by treatment with chloroacetyl chloride. Treatment with hydrazine completes the synthesis of 168. 

Similarly, reaction of hydrazidoyl halides with sodium cyanate ( ), potassium selenocyanate and sodium azide has been reported. For example, decarboxylation occurs when the carboxylic acid derivative XLIV is treated with sodium azide, and the tetrazole derivative XLVI is isolated... 

A standard condition has been optimized for this reaction, in which the aryl amine is diazotized in 10 times its amount of acetic acid, followed by the addition of one equivalent of cuprous halide in hydrohalic acid. Under these conditions, the acetate salt of aryl amine is relatively soluble, and less froth and tarry material are formed during diazo transformation. In addition, chlorination, bromination, and iodonation of p-haloaniline to dihalobenzenes under such standard conditions give almost comparable average yields. Other modifications of this reaction include the formation of phenyl selenocyanate by the reaction with potassium selenocyanate, and aryl nitrile by the reaction with nickel cyanide. Moreover, this reaction has been extended to the preparation of phenyl thiocyanate, phenyl isothiocyanate and aromatic sulfonyl chloride. ... 

---