Condensation aprotic

In aprotic conditions acetic anhydride sodium acetate induces formation of a fused ring through an intra molecular condensation. It results in a pyrrolo[2,l-fc]thiazole (39), which constitutes an interesting intermediate for the synthesis of dyes (Scheme 18) (40). 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

Condensation ofDianhydrides with Diamines. The preparation of polyetherknides by the reaction of a diamine with a dianhydride has advantages over nitro-displacement polymerization sodium nitrite is not a by-product and thus does not have to be removed from the polymer, and a dipolar aprotic solvent is not required, which makes solvent-free melt polymerization a possibiUty. Aromatic dianhydride monomers (8) can be prepared from A/-substituted rutrophthalimides by a three-step sequence that utilizes the nitro-displacement reaction in the first step, followed by hydrolysis and then ring closure. For the 4-nitro compounds, the procedure is as follows. 

The Dnseoc group was developed as a base-labile protective group for the 5 -hydroxyl in oligonucleotide synthesis. It is cleaved with DBU in aprotic solvents. The condensation of oligonucleotide synthesis can be monitored by UV detection at 350 nm or by fluorescence at 530 nm of the liberated vinylsulfone. ... 

A very efficient method for annulations158 is based on the addition of lithium or silyl enolates to a-silylated enones as a key step. The diastereoselective 1,4-addition is followed by an aldol condensation. This procedure allows Michael additions under aprotic conditions, whereby the silyl substituent stabilizes the enolate of the Michael adduct preventing polymerization of the enone, 59 l63. 

Weiss et al. (1984) showed that A V-bis-silylated anilines react in aprotic dichloro-methane with generation of diazonium salts and formation of the non-nucleophilic hexamethyldisiloxane (Scheme 2-28). The authors indicate that the monosilylated aniline C6H5NHSi(CH3)3 reacts in many cases in an analogous way. This seems surprising, since the hydroxytrimethylsilane HOSi(CH3)3 that is formed is a potential proton donor, as it will rapidly condense to give (CH3)3SiOSi(CH3)3 + H20. 

Two-shot techniques for acyclic diene metathesis, 435-445 for polyamides, 149-164 for polyimides, 287-300 for polyurethanes, 241-246 for transition metal coupling, 483-490 Anionic deactivation, 360 Anionic polymerization, 149, 174 of lactam, 177-178 Apolar solvents, 90 Aprotic polar solvents, 185, 338 Aprotic solvents, low-temperature condensation in, 302 Aqueous coating formulations, 235 Aqueous polyoxymethylene glycol, depolymerization of, 377 Aqueous systems, 206 Ardel, 20, 22... 

The first involved a chemoselective 2-step sequence (1) selective O-pivaloylation of OH-6 and OH-2 2) selective oxidation at C-3 to afford the target ketone (Scheme 28). When the condensation with HSCN was carried out in refluxing ethanol, a good overall transformation yield of 83% was obtained two OZTs were formed in 22% (R = H) and 61% (R = Et) yield, respectively. Performing the reaction in a mixture of aprotic solvents (THF/DMF) afforded the target OZT (R + H) in 79% yield (Scheme 28). 

The compounds are obtained by coupling diazotized 1-aminoanthraquinone onto 2-hydroxy-3-naphthoic acid, followed by separation, drying, and conversion into the azo dye acid chloride. Condensation with amines (structure 81) is achieved in an aprotic organic solvent. 

Finer particle sizes are obtained if l,9-anthrapyrimidine-2-carboxylic acid chloride is condensed with 1-aminoanthraquinone in a dipolar aprotic solvent (such as N-methylpyrrolidone) at a temperature between 70 and 110°C. The reaction may be accelerated by using a proton acceptor such as triethylamine or tert-butanol,... 

Table 1. Grafting of 3-aminopropyl groups on mesoporous silica obtained in polar-protic, polar-aprotic and non-polar solvents, surface area and catalytic efficiency for Nitroaldol condensation of 4-hydroxybenzaldehyde and nitromethane [22]. 

Condensation of the sodium salt of phenylacetonitrile with 1,3-dibromobulane gives an isomeric mixture of l-cyano-2-methyl-1-phenylcyclobutanes 21 and 22.30 The effects of solvents on this cyclization reaction have been studied. While solvents of low dielectric constants seem to favor the formation of 21, the ratio of 21 to 22 was found to be almost 1 1 in dipolar aprotic solvents, as can be seen in the following table.30... 

Bacon and Hill (3) have found that copper (I) oxide can be conveniently used as a source of the copper catalyst. They performed the condensation simply by heating the phenol and aromatic halide in the presence of the oxide in the aprotic dipolar solvents, collidine, pyridine, dimethyl sulfoxide or dimethyl formamide. Neither of these groups appear to have used these milder conditions for the preparation of polymers. 

The reaction sequence described herein enables the preparation of heteroaromatic stilbenes by direct condensation of methyl or methylene groups with anils derived from aromatic aldehydes, in the presence of strong base, and in certain dipolar aprotic solvents. 

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