Aryl isocyanates and N,N-diary1 carbodiimides are known to homodimerize and trimerize, yielding 1,3-diazetidines and hexahydro-s-triazine derivatives.(l,2) Both heterocumulenes are also known to react with each other via a [2 + 21 cycloaddition, giving 2-arylimino-1,3-diaryl-diazetidinones.(3) Cycloadducts derived from two moles of aryl isocyahate and one mole of N,N'diarylcarbodiimide or vice versa have not been synthesized so far.(4,5) We found that 1,3,5triaryl-2-phenylimino-4,6-dioxo-hewhydro-s-tiSazines 2 (2:l cycloadducts from aryl isocyanates and N,N'-diary1 carbodiimide) can be prepared conveniently from 1,3-diphenylz2-phenyliminodiazetidinone 1 and aryl isocyanates or bis-(chlorocarbonyl) arylamines 4 and N,N',N"-triphenyl guanidine.
On treatment of a suspension of 1 in excess phenyl isocyanate with gaseous hydrogen chloride at room temperature, 1,3,5-triphenyl-2-phenylimino~,6-dioxohe~hyd~~-t~azine 3a is formed in 82% yield. Other aryl isocyanates such as p-tolyl and m-chlorophenyl isocyanate can also be used in the reaction, resulting in the formation of hexahydro+-triazine derivatives derived from two different aryl isocyanates. Of the two possible structural isomers, 2 and 3, which can be expected from a reaction with a different isocyanate, only 2 is obtained.(6)