Cumulated double bonds carbodiimides

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

Thus, the carbodiimides CXIII, having a phosphorus atom attached to the cumulative double bond system, were obtained for the first time ( ). 

Other halides which have been added to carbodiimides include phosphorus trichloride, phosphorus oxychloride, sulfur dichloride, sulfuryl chloride, and thionyl chloride ( ), and product formation was judged on the basis of disappearance of the cumulative double bond absorption of the carbodiimides. 

In addition to activated olefins, other double-bond substrates, such as carbonyl and thiocarbonyl compounds and azomethines have been used ( ). Likewise, heterocumulenes, such as carbon disulfide, isocyanates, isothiocyanates, carbodiimides, and N-sulfinylamines have been added to nitrile imides ( ). While usually reaction occurs across one of the cumulative double bonds, with carbon disulfide only the bis-adduct LVIII could be isolated ( ). 

The silatropic process combined with the addition reaction can be realized with quite a number of compounds, including carbodiimides [Eq. (6a)], isocyanates, carbon disulfide [Eq. (6b)], or carbon dioxide [Eq. (6c)], which exhibit cumulated hetero double bonds. The first step, insertion between the P-Si bond, is followed by a silyl migration (32-35). 

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