Carboxylated preparation

The same methodology was also used starting from the ethyl 6-amino-7-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate, prepared by reduction of the nitro derivative. The requisite nitro derivative was prepared by nitration of ethyl 7-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate. A second isomer was prepared from 4-chloro-3-nitroaniline by reaction with diethyl ethoxymethylene-malonate, subsequent thermal cyclization, and further ethylation because of low solubility of the formed quinolone. After separation and reduction, the ethyl 7-amino-6-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate 32 was obtained. The ort/io-chloroaminoquinolones 32,33 were cyclized to the corresponding 2-substituted thiazoloquinolines 34 and 35, and the latter were derivatized (Scheme 19) (74JAP(K)4, 79CPB1). 

A number of 4,5,6,7-tetrahydrobenzo[6]thiophenes have been synthesized recently from cyclohexanones (Section IV, A). Hydrolysis of ethyl 2-amino-4,5,6,7-tetrahydrobenzo[i>]thiophene-3-carboxylate, prepared in this way, affords the free amino acid, which readily loses carbon dioxide to yield 2-amino-4,5,6,7-tetrahydrobenzo[6]thiophene in 71% overall yield.254... 

The Nd-carboxylates prepared by the described large-scale methods contain excess carboxylic acid and excess water. The viscosities of Nd carboxy-lates in organic solvents are significantly reduced by the presence of these two impurities which also have an impact on the course of the polymerizations and on various features of the resulting BR (Sect. 2.2.3). 

Various stereoselectively a-, a,p- or JJ-deuterated carboxylates prepared form deute-rated substrates in H2O or by reduction of nonlabelled substrates in H20 buffer and freeze dried microorganisms. 

Almost all of the 2-hydroxy carboxylates prepared were analysed on a Chiral-l/HPLC column by ligand exchange chromatography using a dilute copper sulphate solution as eluent. As already shown a-values for both enantiomers of aromatic as well as for aliphatic 2-hydroxy acids are in the range of 1.3-1.8 with higher retention times for the (i )-2-hydroxy acids (60). For details see (43). 

Phosphole sulfides are frequently stable, unlike oxides which rapidly dimerize, and can be used as precursors of phospholes by simple reduction methods. In another approach <80NJC683>, this stability was taken advantage of for the introduction of the carboxylate group on the 3,4-dimethyl-phosphole ring (Scheme 83). The sulfide forms a carbanion (270) which can be quenched with diethyl oxalate to form a phosphole sulfide 2-carboxylate. This was converted to the phosphole by removing the sulfur with a more nucleophilic phosphine (tri- -butylphosphine or tris-(2-cyano-ethyOphosphine). The phosphole-2-carboxylates prepared this way ((271) and (272)) were significantly more stable than the 3-carboxylates and could be stored at room temperature. 3,4-Dimethyl substitution is well known to increase the stability of phospholes, and at present it is unknown if this substitution pattern or the position of the carboxylate is responsible for the increased stability. 

Similarly, hard Lewis acids, including SnCL, TiCLt, and (C2H5)2A1C1, also afforded the frani-oxazoline 808 as the major product. Some selected examples of cis-2-oxazoline-4-carboxylates prepared by this method are shown in Table 1.58. 

Hydroxy-quinoline carboxylates, prepared using the Could-Jacobs reaction, have also been frequently used as precursors for the synthesis of biologically interesting quinoline compounds. For example, the syndiesis of... 

The only other useful aryne precursor of the zwitterionic type is diphenyliodonium-2-carboxylate, prepared from 2-iodobenzoic acid. It is much more thermally stable than benzenediazonium-2-carboxylate, decomposing in the range 160-200 °C with elimination of carbon dioxide and iodobenzene (Scheme 7.15). 

Aziridine-2-carboxylates Preparation, nucleophilic ring opening, and ring expansion 12H(85)2837. 

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