Acid halides precursor

A simple two-step synthesis of 5H-alkyl-2-phenyloxazol-4-ones has been reported by Trost and coworkers (Scheme 6.209) [377]. a-Bromo acid halides were condensed with benzamide in the presence of pyridine base at 60 °C to form the corresponding imides. Microwave irradiation of the imide intermediates in N,N-dimethylacetamide (DMA) containing sodium fluoride at 180 °C for 10 min provided the desired 5H-alkyl-2-phenyloxazol-4-ones (oxalactims) in yields of 44—82%. This class of heterocycles served as excellent precursors for the asymmetric synthesis of a-hydroxycar-boxylic acid derivatives [377]. 

All BMI building blocks and maleimide-terminated oligomers discussed previously are synthesized from the corresponding polyamine precursor and maleic anhydride simply because of economic reasons. However, there are other synthetic methods available, for instance, the reaction of a functionalized monomaleimide with a polyfunctional monomer or oligomer. Such a functionalized monomaleimide is maleimido benzoic acid or its acid halide. These were used to synthesize maleimide-terminated polyamides (39, 40) or polyesters (41), respectively. 

In 1994, Buzek et al. (109) reported that the allyl cation could be prepared from a variety of halide precursors, e.g., allyl chloride or cyclopropyl bromide, on SbF5 at cryogenic temperature, based on the infrared spectrum of the products. Those workers challenged BGW s claim of the persistent allyl cation based on the discrepancy between the isotropic 13C shift in the zeolite and that calculated at MP2/6-31G. This was one of the first examples of the use of chemical shift calculations to interpret (and in this case challenge) an NMR study of a species on a solid acid. 

Smith et al. adapted Sheehan and Izzo s synthesis of 2-aryl-4(5//)-oxazolones and developed a general synthesis of 2-alkyl-4(5//)-oxazolones. The reaction between acid halides and AgNCO followed by treatment with ethanol-free diazomethane produced oxazolones 252, which served as precursors to triflyloxyoxazoles 253 (Scheme 74). Triflyloxyoxazole 253 (R = CH2Br) was utilized as a difunctional linchpin for the bidirectional assembly of the natural product phorboxazole <2001JA10942>. 

The preparation of the acid derivatives is organized according to their precursors. The synthetic method of choice in a particular case will depend on a number of factors of which the presence of other functional groups in the molecule under study is not the least important. The methods will be evaluated with respect to their scope of application. The chemistry of acid halides has been reviewed. Methods of preparation are treated in Houben-WeyP as well as in other reference books. This applies also to acid anhydrides and a-ketonitriles. ... 

Imidazole acid halides are very reactive and are easily converted into other acid derivatives <82JHC56l, 84JOC1951>. They cannot, however, be used as precursors of acetyl functions in reaction with lithium dimethylcopper <92JHCl02i>. 

Mutually reactive functional group combinations like acid halide and alcohol in the same precursor are recognized in the precursor evaluation routine. The user specifies to EVAL whether such precursors should be deleted. 

The mechanism of the Ni catalyzed carbonylation is depicted in Scheme 1.5 [17]. Ni(CO)4 is formed from various Ni precursors by a reductive reaction with CO. The hahde ions are important since they are the source of HX that can be oxidatively added to Ni(CO)4, forming HNi(C02)X. The latter reacts with olefin in an anti-Markovnikov way, giving the hnear alkyl-Ni species. The insertion of CO into the alkyl-Ni bond forms the acyl-Ni complex that decomposes under reductive elimination into the corresponding acid halide and Ni(CO)4. The former reacts with the nucleophile so that the product is set free and HX is regenerated. 

Most of the available evidence points to a rate-controlling substitution by the amine on the acyl halide, like that for acylation by esters, although other mechanisms involving ionisation to give an acyl ion which then attacks the amine, are, in principle, possible. However, since ionisation of acid halides occurs most readily in acid media, conditions under which the amine would be protonated and therefore unreactive, any mechanism involving this process as the precursor to reaction seems unlikely. Also, slow ionisation of the acyl halide implies that the rate of reaction should be independent of the amine and... 

They include natural polymers such as silk and synthetics such as nylons. Nylon polymers first were synthesized by Wallace Carothers and CO workers at Du Point in the late 1920s and 1930s. They are derived from carboxylic acid and amine precursors by both condensation and ring opening polymerization. They are commonly named by adding to the word nylon, a number equal to the number of carbons in the parent compounds. Thus, nylon 6.6 is the product of the condensation reaction between hexamethylenediamine, NH2(CH2)eNH2, or HMD A, and adipic acid or its acid halide and methyl ester. 

Ionic liquids formed by treatment of a halide salt with a Lewis acid (such as chloro-aluminate or chlorostannate melts) generally act both as solvent and as co-catalyst in transition metal catalysis. The reason for this is that the Lewis acidity or basicity, which is always present (at least latently), results in strong interactions with the catalyst complex. In many cases, the Lewis acidity of an ionic liquid is used to convert the neutral catalyst precursor into the corresponding cationic active form. The activation of Cp2TiCl2 [26] and (ligand)2NiCl2 [27] in acidic chloroaluminate melts and the activation of (PR3)2PtCl2 in chlorostannate melts [28] are examples of this land of activation (Eqs. 5.2-1, 5.2-2, and 5.2-3). 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

Historically, the rhodium catalyzed carbonylation of methanol to acetic acid required large quantities of methyl iodide co-catalyst (1) and the related hydrocarboxylation of olefins required the presence of an alkyl iodide or hydrogen iodide (2). Unfortunately, the alkyl halides pose several significant difficulties since they are highly toxic, lead to iodine contamination of the final product, are highly corrosive, and are expensive to purchase and handle. Attempts to eliminate alkyl halides or their precursors have proven futile to date (1). 

Apart from the alkyl halide-Lewis acid combination, two other sources of carbo-cations are often used in Friedel-Crafts reactions. Alcohols can serve as carbocation precursors in strong acids such as sulfuric or phosphoric acid. Alkylation can also be effected by alcohols in combination with BF3 or A1C13.37 Alkenes can serve as alkylating agents when a protic acid, especially H2S04, H3P04, and HF, or a Lewis acid, such as BF3 and A1C13, is used as a catalyst.38... 

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