Bonds reaction with cyanamide

An alternative mechanism [8] entails reaction of cyanamide (or dicyandiamide) with the dye phosphonate to give an O-acylisourea derivative (7.47). This is able to react directly with cellulose to form dye-fibre bonds, urea being released as the anticipated by-product (Scheme 7.31). In support of this mechanism, it is known that O-acylisourea derivatives of arylcarboxylic acids react readily with alcohols and this constitutes an efficient route for the preparation of carboxylic esters [44]. 

The reaction of dichloromethylsilane with cyanamide affords a highly crosslinked polymer caused by hydrosilation reactions between the carbodiimide and the Si-H bond. Gels are obtained in the reaction of dimethylchlorosilane with bis(trimethylsilyl)carbodiimide. Using TiCU or Ti(NEt2)4 with bis(trimethylsilyl)carbodiimide produces poly(titanium... 

Because of their predictable behavior and reactivity, thioacyl isocyanates comprise the bulk of this work, and extensive studies of their [4 + 2] reactions with olefins,83 enamines,84 enol ethers,843 thioacyl isocyanates,85 imines,85 1 86 carbodiimides,84387 isocyanates,843 azirines,88 /3-enaminoke-tones,89 dianils,86d azines,90 hydrazones,91 imidazoline-4,5-diones,92 aryl cyanates,93 disubstituted cyanamides,93 aldehydes,94 ketones,94 ketenes,94 alkyl or aryl iminodithiocarbonates,95 and the carbon-carbon double bond of ketenimines96 have been detailed. In an extensive comparative study of the [4 + 2] cycloaddition reactions of thioacyl isocyanates, the heterocu-mulenes bearing strong electron-withdrawing substituents were found to be more stable and less prone to participate in cycloaddition reactions.84 Representative examples are summarized in Scheme 9-IV. 

The mechanism of the reactions of aromatic unsaturated ketones with malonamide was described in [154]. The expected product of (3-addition— <5-ketamide—was isolated and fully characterized. The proposed mechanism of the formation of the terahydropyridone cycle in [154] was similar to one suggested in [134, 153] for cyanamide. The first stage of the reaction is an addition of the CH-acid to the ethylene bond of the unsaturated ketone and generation of the (3-adduct, which can easily undergo a cyclization leading to dihydro derivatives of 2-pyridone 146 (Scheme 3.45). 

Cyclic addition reactions of 16a with diynes or cyanamide are interpreted as being initiated by an electrophilic attack of the cyanamide or the terminal carbon atom of a C=C bond. Both result in ring expansion and the formation of 2,4-As,As-diphosphapyridine 39 <1998ZNB443> or l,3-A5,A5-diphosphabenzenes 40, respectively (Scheme 10). The diyne reaction is not limited to conjugated systems. 1,5-Hexadiyne and 1,7-octadiyne can be used as well <1997JOM(529)223>. 

To sum up, the addition of an unsaturated system X=Y=Z to Hector s base may be represented31,33 by the reaction sequence of Scheme 3, in which the final step involves merely a proton shift, and a rotation about a C—N bond. In the case of the isothiocyanate esters, factors as yet unknown terminate the reaction at the simple addition stage 25, but permit it to continue to 26 in the case of cyanamides and carbon disulfide. The dimethylated Hector s base does not form adducts with any of these reagents.31... 

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>. 

In aqueous methanol, the oxidation of catharanthinic acid (236) with mercuric acetate gives a product (239), obtained by oxidative decarboxylation and rearrangement. A possible mechanism for this reaction is illustrated (Scheme 32). An alternative preparation of (239) involves the von Braun degradation of catharanthine (234), which severs the 21-Nb bond to give a cyanamide derivative (240). Saponification of (240) followed by bromodecarboxylation and removal of the N-cyano-group affords a tetracyclic amino-diene (241) which, on oxidation in methanol solution, gives the epimers (239)." ... 

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