Studies of Acyl and Thioacyl Isocyanates. VIII. Cycloaddition Reactions of Benzoyl and Thiobenzoyl Isocyanates with Carbodiimides

Abstract

Abstract The investigations of cycloaddition reactions of benzoyl and thiobenzoyl isocyanates with carbodiimides have shown that the adducts formed from benzoyl isocyanates and N,N′-dicyclohexylcarbodiimide are the corresponding (4+2) cycloadducts, and not the (2+2) cycloadducts proposed by Neidlein. The reaction of isocyanates with N,N′-diphenylcarbodiimide at 0°C gave (2+2) cycloadducts, which were thermally isomerized into the corresponding (4+2) cycloadducts. Benzoyl isocyanates reacted with N-cyclohexyl-N′-phenylcarbodiimide to give (4+2) cycloadducts of isocyanates to the cyclohexyl-N=C bond in the carbodiimide. On treatment with neutral alumina, (4+2) cycloadducts were easily isomerized into 1,3,5-triazines. Thiobenzoyl isocyanate reacted with both the N=C bonds of the carbodiimide to afford two isomeric (4+2) cycloadducts. It has been found that benzoyl isocyanates reacted with N-phenyl-N′-o-tolylcarbodiimide to yield the corresponding (4+2) cycloadducts of isocyanates to the o-tolyl-N=C bond and/or the isomeric 1,3,5-oxadiazin-6-ones, depending on the nature of the substituent in the isocyanate. Reaction paths for the formation of the product are also discussed.