Carbon nitrogen double bonds, formation

Polyurethane Formation. The key to the manufacture of polyurethanes is the unique reactivity of the heterocumulene groups in diisocyanates toward nucleophilic additions. The polarization of the isocyanate group enhances the addition across the carbon—nitrogen double bond, which allows rapid formation of addition polymers from diisocyanates and macroglycols. 

For reviews of reactions of carbonyl compounds leading to the formation of C=N bonds, see Dayagi, S. Degani, Y. in Patai The Chemistry of the Carbon-Nitrogen Double Bond Ref. 40, p. 64 Reeves, R.L. in Patai, Ref. 2, p. 600. 

In the base-catalysed dehydration for oxime formation a significant development of the carbon-nitrogen double bond in the TS is assumed. 

The carbon-nitrogen double bond of phenanthridine can be reduced selectively by hydrogenation over Raney nickel, and attempted reductive dechlorination of 6-chloro derivatives in the presence of this catalyst normally results in the formation of the corresponding 5,6-dihydro compounds.106 Hydrogenations over palladium catalysts are more successful.203 325 Desulfurization of phenanthridinthione... 

Treatment of an ethereal solution of 4-oxo-dihydro-l,3-diaza-anthracene (108) with lithium aluminum hydride reportedly resulted in the reduction of only the 1,2-carbon-nitrogen double bond with 4-oxo-l,2,3,4-tetrahydro-l,3-diazaanthracene (109) being the only product isolated.134 Apparently conditions were not sufficiently vigorous for the further reduction of the tautomeric form of 109, or possibly the formation of a complex with the aluminohydride pre-... 

This reaction was intensely investigated by Mloston et al. In a classical, but not general reaction, they observed that heating aromatic or aliphatic thioketones [251, 252], thionoesters [253] and dithioesters [252, 253] with aryl-or benzylazides led to the formation of a carbon-nitrogen double bond. A [3+2] cycloaddition was assumed, with successive elimination of nitrogen and sulfur. 

The mechanism for amide formation promoted by DCC is shown in Figure 26.4. The carboxylic acid first reacts with DCC to form an intermediate that resembles an anhydride, but with a carbon-nitrogen double bond in place of one of the carbonyl groups. 

In a similar manner, imines 50 with various ancillary groups X, such as ethoxy-carbonyl, 2-pyridyl, or 2-thiazolyl, are also converted into lactams 51 in mod-erate-to-good yields (Eq. 24) [38]. The [2+2+1] lactam formation using a chiral substrate 52, ethylene, and CO quantitatively furnished the spiro lactam 53 (Eq. 25) [39]. The cycloaddition exclusively took place at the carbon-nitrogen double bond next to the oxazine oxygen atom, although 53 was obtained as a diastereomeric mixture. 

The final example is slightly different from the previous protocols in two ways. First, the IMP is generated by Sn2 displacement of a benzotriazole moiety. The IMP then opens an epoxide, which generates a betaine with an extra carbon atom between phosphorus and the negatively charged oxygen. Collapse of this betaine results in the formation of an aziridine as opposed to a carbon-nitrogen double bond. 

The most commonly used of these three bond classes is the formation of bond b . Formation of bond b typically occurs through an intramolecular alkylation of a nitrogen atom. A second highly prevalent method for the formation of the type I structure is the formation of bonds b and c from addition of a nitrogen across a carbon-carbon double bond. A final rarely used route is the formation of bonds c and e through the intramolecular addition of a carbene across and carbon-nitrogen double bond. Methods in which bond a is formed are rare in terms of simple fused-ring aziridines but several examples can be found in Section 1.02.7 in the discussion of the mitomycin family of alkaloids (Scheme 1). 

For a review of the formation and reactions of imino chlorides, see Bonnett, R., in Patai, S. The Chemistry of the Carbon-Nitrogen Double Bond, Wiley, NY, 1970, pp. 597-662. 

Dehydrogenations, which involve the elimination of hydrogen Ifom organic molecules, lead to compounds containing double bonds, multiple bonds, or aromatic rings. For practical reasons, only the formation of carbon-carbon double bonds, of carbon-nitrogen double bonds in cyclic amines, and of aromatic rings (both carbocyclic and heterocyclic) will be discussed in this chapter. The conversion of alcohols into aldehydes and ketones and of amines into imines and nitriles will be discussed in the chapter Oxidations (Chapter 3). 

Example 4. Polyurethane formation, in which the alcohol adds across the carbon nitrogen double bond of the isocyanate function (0 = C = N-R) to form the urethane (-0-C0-NH-) link without loss of a small molecule, represents an exception to this general recognition feature of polycondensations. Bakelite is one of several possible products from phenol-formaldehyde resins, and these may or may not involve loss of a small molecule. This more complicated process will be discussed in further detail later. 

The [3+2] cycloaddition of allylsilanes is applicable to imines and iminium salts [419, 484, 485], Highly substituted pyrrolidines can be synthesized with high diastereo and enantio control by reaction of homochiral crotylsilanes with carbon-nitrogen double bond generated in situ from acetals and methyl carbamate (Scheme 10.174) [419]. The cycloaddition to N-tosylaldimines of aromatic aldehydes proceeds with excellent 2,4-ds selectivity whereas the stereoselectivity with aliphatic aldimines is rather low [484]. With N-tosylaldimines, fhe formation of [2+2] adducts is not observed (vide infra). 

The formation of 111 (Scheme 32) has been rationalized as a [2-1-2] cycloaddition of one of the two carbon-nitrogen double bonds of the dicyclohexylcarbodiimide to the Cp-C. double bond of the allenylidene of 43 to give the intermediate 113, which rapidly evolves into 114, by an Alder-ene reaction, where the C -Cp double bond of 113 acts as an enophile. The presence... 

Treatment of LXXXV with ethyl formate gave the C-10 hydroxy-methylene derivative, which was converted to the thioketal LXXXVI by means of trimethylene-bis- -toluenethiosulfonate. Mercuric acetate in aqueous acetic acid furnished a bright yellow a-diketone, which formed the enol acetate (LXXXVII) on treatment with acetic anhydride in pyridine. Alkaline treatment of LXXXVII in the presence of air gave the tropolone LXXXVIII. Reductive removal of the sulfur atom with Raney nickel, saturation of the carbon-nitrogen double bond, and acetylation provided dLcolchiceine (LXXXIX), identical with an authentic specimen. 

At pH 4.0, proton elimination, which leads to formation of the nitrile, is the dominant reaction process. These reaction products are the same as those found for the acid-catalyzed degradation of aldicarb (Bank and Tyrrell, 1984). Nucleophilic addition of water across the carbon-nitrogen double bond (pathway b) results in the formation of an unstable complex, which decomposes readily by cleavage of the carbon-nitrogen bond to give the aldehyde, methylamine, and carbon dioxide. 

Carbon-carbon and carbon-nitrogen double bonds were utilized as an entry point to A-functionalization by formation of new carbon-nitrogen bond in mechanosynthetic reactions such as aza-Michael reaction and aminohalogenation of olefins. 

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