Anions isocyanate

Under these conditions, silver-assisted electrocyclic ring opening provided the haloallyl cation, which was subsequently trapped by isocyanate anion. Interception of the cationic species with isocyanate was successful since bromide was removed from the reaction mixture as a precipitate (AgBr). Finally, treatment of intermediate 9 with methanol furnished the desired carbamate in 96% yield. This example demonstrates the usefulness of the silver(I)-mediated process. Removal of free halide from the reaction mixture affords a long-lived cationic species that can be captured by a different nucleophile, such as solvent, the silver(I) counteranion, or an intramolecular nucleophile. This reactivity has been exploited in many different ways throughout the years and is examined in greater detail later in this chapter. 

The structure of the enniatin B complex with potassium iodide has been studied by X-ray crystallography Unfortunately, from this investigation it could not be concluded with certainty whether the metal ion is entrapped in the central cavity or, instead, occupies a site between two adjacent ligand molecules. An arrangement of the latter type has been observed in the crystal structure of the 1 1 complex between RbNCS and the synthetic LDLLDL isomer of enniatin B In this case, Rb" ions are coordinated by five carbonyl oxygens (three of the upper and two of the lower depsipeptide molecules) and the nitrogen atom of the isocyanate anion, thus forming infinite sandwiches. 

An exclusive complex of this type was actually found also in the crystalline state for the KNCS complex of the smaller [2.2.1] cryptand From molecular models, the cavity radius of this ligand was estimated to be 1.1 A which is too small for potassium to enter. As a result, occupies a site in the 18-membered ring rather than in the central cavity (see Fig. 38), thus resembling the coordination of K" by [18]crown-6. Additionally, the potassium ion is bonded to the isocyanate anion whereas anions are generally not coordinating to alkali metal ions in inclusive cryptates. 

H-pyrane] derivatives in the presence of isatins, malononitrile, and acetylacetone/ethyl 3-oxobutanoate [103]. Yan and coworkers showed in 2012 that chiral tertiary amine-thiourea (158) derived from quinine can catalyze a three-component reaction between isatins 118, malononitrile (119), and a-phenyl-isocyanoacetate (217) (Scheme 2.75) [104]. The process affords dihydropyrryl-spirooxindoles 218 and involves an initial Knoevenagel condensation of 118 and 119 followed by the nucleophilic anion attack of 217 (see the key transition state intermediate on Scheme 2.75). Final intramolecular cyclo-addition affords the expected compounds where H bond interactions are supposed to direct the attack of isocyanate anion and, consequently, contfol the enantioselectivity. One year later, Xu s group used a bifunctional cinchona-based squaramide to catalyze multicomponent cascade reaction to synthesize spiro[pyrrolidin-3,2 -oxindoles] via 1,3-proton shift and [3h-2]... 

The result of the double C-N disconnection in the heterocyclic ring is the two target molecules of the next generation, a-keto-cyclopentane carboxylic acid TM 7.1a and N-cyclohexylurea TM 7.1b. On refra-Dieckmann disconnection, TM 7.1a leads to diethyl adipate (Sect. 4.3.3, Scheme 4.23) and TM 7.1b affords the isocyanate anion and cyclohexylamine. 

In the proposed synthesis, silicon tetraisocyanate is used as a convenient source of the isocyanate anion (Scheme 7.2) [5]. 

Enamines and enolate anions react with benzofuroxan to give quinoxaline di-A -oxides (Scheme 38) (69AHC(10)1). Sydnones (274) with phenyl isocyanate give 1,2,4-triazoles (275) (76AHC(19)l), and from (276) the intermediate adduct (277) can be isolated (73JA8452). This is one of the few instances in which such primary cycloadducts have been isolated in the oxazole series of mesoionic compounds. 

The waterborne prepolymer process is similar to the prepolymer synthesis described earlier, except that most of the waterborne prepolymers are based on aliphatic isocyanates and contain an internal emulsifier. There are several types of internal emulsifiers, both anionic and cationic. A good summary of these stabilizers is found elsewhere [56], The majority of the waterborne urethanes are anionic dispersions. An internal surfactant, such as dimethylolpropionic acid, is often incorporated into the prepolymer ... 

The chiral bicyclic imidazolidine 74 is deprotonated at the 2 position by s-BuLi and the resulting anion adds to alkyl halides, acid chlorides, chlorofor-mates, phenyl isocyanate, and aldehydes. The use of this compound as a chiral formyl anion equivalent seems to be limited, however, since the diastereoselectiv-ity in the addition to aldehydes is poor and hydrolysis of the products 75 to give aldehydes also produces cyclohexane-1,2-diamine, necessitating isolation of the aldehyde as its 2,4-dinitrophenylhydrazone (96SL1109 98T14255). 

The yV-bromoamide, its anion as well as the isocyanate have been identified as intermediates thus supporting the reaction mechanism as formulated above. 

Fusion of an all cyclic ring onto the piperidine so as to form a perhydroisoquinoline is apparently consistent with analgesic activity. Synthesis of this agent, ciprefadol (68), starts with the Michael addition of the anion from cyclohexanone 56 onto acrylonitrile (57). Saponification of the nitrile to the corresponding acid ( ) followed by Curtius rearrangement leads to isocyanate Acid... 

Alkylation of the protected azetidinyl bromide 61 with the anion from m-trifluormethyl-phenol gives ether 62. Removal of the N-(alpha-methylbenzyl)- protecting group by catalytic hydrogenation gives the secondary amine 63. Reaction of that compound with methyl isocyanate gives the anticonvulsant urea fluzinamide (64) [14]. 

Reaction of dimsyl anion with isothiocyanates gives a-thioamidosulphoxides 478 in 12-59% yield, whereas with isocyanates it affords a mixture of a-amidosulphoxides 479 and methylsulphinylmalonoamides 480, the products of a double addition549 (equation 289). 

In contrast, a-ketosulphoxides react with isocyanates to give the products of a monoaddition only550 (equation 290). Reaction of dimsyl anion with trithiocarbonates 481 followed by alkylation results in the formation of (methylsulphinyl)ketene dithio-acetals 482551 (equation 291). 

Anionic copolymerization involving similar monomer pairs which propagate through a similar chain end occurs rather easily. Examples are the copolymerization involving aldehydes, isocyanate and ketenes, although these are not always random... 

M-substituted 2-pyridones can be prepared by N-alkylation, under basic conditions (pfCa of the amide proton is 11). The resulting anion can then react on either nitrogen or oxygen depending on the conditions employed [24-27]. Also, several direct methods for the construction of N-substituted 2-pyridones have been reported. Two such examples can be seen in Scheme 3 where the first example (a) is an intramolecular Dieckmann-type condensation [28] and the second (b) is a metal-mediated [2 -I- 2 + 2] reaction between alkynes with isocyanates [29,30]. 

For a monograph, see Reutov, O.A. Beletskaya, I.P. Kurts, A.L. Ambident Anions Plenum NY, 1983. For a review, see Black, T.H. Org. Prep. Proced. Int., 1989, 21, 179. Both cyanates and isocyanates have been isolated in treatment of secondary alkyl iodides with NCO Holm, A. Wentrup, C. Acta Chem. Scand., 1966, 20, 2123. 

A useful method to synthesize ten and fourteen-membered ring imides 346 involved an initial condensation of macrocyclic -ketoestes 343 with alkyl or aryl isocyanates and carbodiimides, respectively, in the presence of a base [68]. After a nucleophilic attack of the enolate on the isocyanate C, the resultant amide N anion 344 induced a ring closure by addition to the keto group. Then, the intermediately formed four-membered ring 345 underwent a fragmentation... 

The anionic method of polymerization is most useful for the synthesis of low molecular weight hydroxy-terminated oligomers and polymers that are to be further processed. For example, the treatment of hydroxy-terminated oligomers with isocyanates has been used to obtain polyester-urethanes (9,20), while triblock copolymers (PCL-PEG-PCL) are prepared by initiating the polymerization of e-caprolactone with the disodium alcoholate from polyethylene glycol (26). 

Four years after Doering s discovery of the hygroscopic bromide of the tropylium ion [3" ] (Doering and Knox, 1954), Vol pin et al. (1957) reported that the tropylium ion (pXr+ 3.88) gives a covalent compound with acetate ion (pXb 9.24) but not with isocyanate ion (pK 10.1). This suggests that an anion with pXb greater than 10.1 would give a salt with the tropylium ion. 

C09-0108. Carbon, nitrogen, and oxygen form two different polyatomic ions cyanate ion, NCO, and isocyanate ion, CNO". Write Lewis stmctures for each anion, including near-equivalent resonance structures and indicating formal charges. 

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