Isothiocyanates, addition alkenes

In a manner analogous to classic nitrile iinines, the additions of trifluoro-methylacetonitrile phenylimine occur regiospecifically with activated terminal alkenes but less selectively with alkynes [39], The nitnle imine reacts with both dimethyl fumarate and dimethyl maleate m moderate yields to give exclusively the trans product, presumably via epimenzation of the labile H at position 4 [40] (equation 42) The nitrile imine exhibits exo selectivities in its reactions with norbornene and norbornadiene, which are similar to those seen for the nitrile oxide [37], and even greater reactivity with enolates than that of the nitnle oxide [38, 41], Reactions of trifluoroacetomtrile phenyl imine with isocyanates, isothiocyanates, and carbodiimides are also reported [42]... 

A single report of the addition of sodium azide to cyclohexene in the presence of iodine under phase-transfer catalytic conditions to produce 2-iodocyclohexanyl azide has the potential for extension to other alkenes [17], The analogous reaction of cyclohexene with potassium thiocyanate and iodine produces 2-iodocyclohexyl isothiocyanate (17%) and 2-iodocyclohexanyl thiocyanate (61%). Similar products are obtained with other alkenes [17],... 

Exposure of alkenes to a combination of 4 and trimethylsilyl isothiocyanate leads to the formation of 1,2-dithiocyanates [Eq. (8)] [28]. The reaction involves the formation of bis(thiocyanato)-A3-iodane by a ligand exchange. The decomposition of this iodane leads to the formation of thiocyanogen, which in turn undergoes the anti electrophilic addition to olefins. 

Admixture of BAIB with two equivalents of trimethylsilyl isothiocyanate in dichloromethane leads to the rapid formation of thiocyanogen and iodoben-zene, presumably via [bis(thiocyanato)iodo]benzene (Scheme 10) [32]. The addition of alkenes to such solutions affords vzcmaZ-dithiocyanatoalkanes. Cyclohexene and its 1-methyl analog were converted exclusively to the transadducts under these conditions, while dihydropyran gave a 1 1 mixture of cis-and trans-isomers. 

A,-(Trimethylsilylmethyl)thioureas are readily accessible via the addition of an amine to the corresponding isothiocyanate. They are good starting materials for preparing 2-amino-A1-pyrroline derivatives via their corresponding azomethine ylids. This is illustrated by condensation with maleimide and different alkenes.245,469... 

Phenylseleno thiocyanate rapidly undergoes addition to alkenes without the presence of a catalyst, producing -thiocyanates and/or /1-isothiocyanates. The stereoselectivity of the addition is less predictable than with other selenenyl electrophiles. 

Cyclisation of the allyl ether shown having an azadiene and an alkene system occurred by an intramolecular Diels-AkJer addition to afford a route to a tricyclic thiazine (ref. 154). Cyclohexyl isothiocyanate has also been used in the initial step. 

Addition of thiocyanic acid to alkenes is rather interesting in view of the am-bident nature of the thiocyanate ion. Norbornene gives a mixture containing 90% isothiocyanate and 9% thiocyanate (34), suggesting considerable hardness of the cationic carbon. In contrast, addition of HNCS to acrylic esters leads to thiocyanate adducts exclusively. The S end is employed to bond with the P carbon of the unsaturated acyl system. It should be noted that neutralization of tropylium fluoroborate with NaSCN yields cycloheptatrienyl isothiocyanate (35). 

Reviews cover the topics alkynethiolates in synthesis " oxygen-exchange reactions of sulphoxides sulphonyldiazomethanes C—S bond cleavage acyl isothiocyanates radical reactions of sulphur compounds addition of sulphenyl halides to olefins " sulphenamidcs mercaptoethylation of amines sulphur as a chiral centre " stereochemistry of S and S " compounds " reductive cleavage of sulphides, synthetic uses of alkene- and alkyne-thiolates, and thio-Claisen rearrangements nucleophilic displacements at sulphur in disulphides aromatic... 

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