Iodothiocyanates and iodoisothiocyanates: synthesis and chemistry

Abstract

The addition of the elements of iodine(I) thiocyanate to alkenes has been examined with various reagents under different conditions, and high conversion into the desired adducts has been achieved. The products, isolated and characterised by spectroscopic and combustion data, are consistent with the intermediacy of a symmetric iodonium ion for cyclohexene and 5α-androst-2-ene, and an open or asymmetric cation for α-aryl alkenes. The ratio of vicinal iodothiocyanate to iodoisothiocyanate varies with reagents used, and also with the structure of the alkene substrates. The iodothiocyanato adduct is the kinetically formed product, and then may rearrange to its thermodynamically more stable iodoisothiocyanato isomer either in situ or separately in the presence of a Lewis acid, thereby providing a simple route to the trans vicinal iodoisothiocyanates which are useful in the synthesis of heterocycles. The application of biphasic systems in the electrophilic addition of iodine(I) thiocyanate to alkenes, with or without added. phase-transfer catalysts, enhance the reaction rate, particularly in the case I of 5α-androst-2-ene. These systems have been used also to advantage for the synthesis of vicinal iodoazides and iodoacetates. The chemistry of vicinal iodothiocyanates and iodoisothiocyanates, such as isomerisation, elimination reduction, and thiirane formation, has been studied briefly. The utility of an iodoisothiocyanate in forming derivatives of 2-thiazolidinone or 2-amino-2-thiazoline provides a new synthetic method in heterocycllc chemistry. The formation of 2-alkyl-2-thiazolines from iodoisothiocyanates, albeit in only low yield, has provided encouraging results for further exploration.