Thiocyanates, alkenes with isothiocyanates

A series of papers detailing a continuation of the study of the synthesis and reactions of uic-iodothiocyanates and -iodoisothiocyanates has been published.Similarly, the treatment of alkenes with thiocyanogen bromide [from equimolar quantitites of bromine and thallium(i) thiocyanate] gives moder-ate-to-high yields of uic-bromothiocyanates. " Unlike the analogous vic-iodothiocyanates, the bromo-compounds are not readily isomerized to the corresponding isothiocyanates. 

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],... 

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. 

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). 

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