CIS-EXO ADDITION OF ISOTHIOCYANIC ACID TO NORBORNENES . SYNTHESIS AND ISOMERIC CONFIGURATION OF HERBICIDE NOREA

Isothiocyanic acid (HNCS) adds predominantly cis and exo to six norbornenes studied, producing norbornyl isothiocyanates in good to excellent yields. This cis-exo addition of HNCS to endo-dicyclopentadiene is utilized to prepare exo-5-isothiocyano-5,6-dihydro-endo-dicyclopentadiene, an intermediate used in the synthesis of the herbicide norea. Norea, which is predominantly exo-5-(3,3-dimethylureido)tetrahydro-endo-dicyclopentadiene, is prepared from the iso thiocyanate in three steps: (1) the isothiocyanate is allowed to react with dimethylamine; (2) the resulting thiourea is converted into the corresponding urea by phosgenolysis and hydrolysis; and (3) the urea is catalytically hydrogenated to norea. Nonpolar media and moderate temperatures favor the cis-exo addition of isothiocyanic acid to endo-dicyclopentadiene. © 1969, American Chemical Society. All rights reserved.