Allyl thiocyanate, rearrangement

Experimental and theoretical studies on the isomerization of allyl thiocyanate to aUyl isothiocyanate have indicated that the transformation proceeds by a [3,3]-sigmatropic rearrangement involving a cychc transition state. A novel tandem [3,3]-sigmatropic rearrangement of allylic thiocyanates (129) followed by a stereo-controlled intramolecular addition of the amino function to the developing isothiocyanate group, has... 

The rearrangement of allylic thiocyanates while also a first-order process shows a much smaller dependence of rate on solvent polarity . The results of the effects of substituents, solvent and salt effects on the rate of reaction seem to indicate that the rearrangement of allylic thiocyanates essentially occurs by way of a nonionic cyclic mechanism , viz. 

Allyl thiocyanate, CH2=CHCH2SC=N, on distillation rearranges to allyl isothiocyanate, CH2=CHCH2N=C==S. Cinnamyl imd crotyl thiocyanates also rearrange the rearrangement of the former occurs without inversion, yielding cinnamyl isothiocyanate that of the latter is accompanied by inversion, yielding a-methylallyl isothiocyanate. 

Sigmatropic rearrangements have also found use in allylic S — N transposition. The rearrangement of allyl thiocyanates to allyl isothiocyanates (equation 27) ° belongs to this class as does the rearrangement of 5-allyl thioimidates (equation 28). ° ... 

The stereoselective formation of imidazolidine thiones via the rearrangement of chiral thiocyanates has recently been reported. Heating allylic thiocyanates such as 255 at 80 °C produced El-mixtures of diastereomeric isothiocyanates 256a in 92%... 

A method which is suitable for the preparation of allylic amines involves the allylation of thiocyanate ion to give the allyl thiocyanate followed by rearrangement (by the mechanism in many cases) to the isothiocyanate, and subsequent hydrolysis . 

The chief product of the reaction is thus allyl iso-thiocyanate (allyl thiocarbimide), a pungent and disagreeable liquid. A small quantity of the normal allyl thiocyanate is also formed, tc ther with traces of tdlyl cyanide and carbon disulphide. As mustard oU consists almost entirely of allyl iso-thiocyanate, and the latter body is easily prepared artificially, there is an artificial oil on the market. This is made by distilling allyl iodide or bromide with alcoholic solution of potassium thiocyanate— a molecular rearrangement to the iso-thioej anic radicle taking place. Thus—... 

Another route to sugar isothiocyanates involves thermal isomerization of the corresponding thiocyanates. Ferrier and Vethaviyasar20,21 and, later, Guthrie and Williams22-23 reported the allylic rearrangement of unsaturated thiocyanates to isothiocyanates see formulas 9-14. 

Organic selenocyanates similarly undergo facile isomerizations but very little information on this is available. Selenocyanates isomerize somewhat faster than thiocyanates and the rate is insensitive to solvent polarity for the allyl compound, but very sensitive to solvent and structure for benzhydryl compounds. It is considered that the mechanisms of rearrangement are closely parallel to those of the thiocyanates. 

This compound undergoes rearrangement the same as ammonium cyanate and thio-urea is obtained. With a soluble mercuric salt ammonium thiocyanate precipitates mercuric thio-cyanate which on heating swells up into phantastic shapes which are known as Pharaoh s serpents. The alkyl thio-cyanates are known and have been discussed (p. 74). Allyl-thio-cyanate is a constituent of oil of garlic. These... 

Isothiocyanates (105) are very reactive molecules, but rather less so than isocyanates. Some are physiologically active and occur as natural products for example, allyl isothiocyanate (105) (R=CH2CH=CH2) is a major component of mustard oil and horseradish root. Isothiocyanates can be prepared by thermal rearrangement of the analogous thiocyanates (111) the latter are obtained by treatment of alkyl halides or tosylates with potassium thiocyanate (110) (Scheme 60). 

Allylic rearrangement of thiocyanates to isothiocyanates has been demonstrated for monosaccharide derivatives, " - " opening up methods for sugar transformations but especially for s mthesizing amino-sugars. " For example, (165) gives (166) by way of the isothiocyanate resulting from thermal isomerization. " The allylic O-methanesulphonyl substituent in... 

Aza-Claisen rearrangement of allylic imidates and thiocyanates in presence of o-xylene under microwave irradiation resulted in corresponding amides and isothiocyanates (Gonda et al., 2007). The reaction rate was enhanced 8-30 and 24-80 times, respectively. 

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