Amide formation urethane

In step growth reactions, on the other hand, neither are specific activated centers present to force the connection of the monomers, nor does the process occur as a cascade reaction. Instead, the monomers are tied together in discreet, independent steps via conventional organic reactions such as ester-, ether-, amide-, or urethane formation. Depending on whether small molecules are set free in the connection step, one distinguishes between polycondensations (2.9) and polyadditions (2.10) ... 

Finally, the strategy should be of interest because it only requires two reactions steps. This is possible because ketimine isolation is not required, and while rarely discussed can be time consuming, may provide mediocre yield, and unnecessarily lengthens the synthesis of amines. Furthermore, all the reagents are already in use by the pharmaceutical industry, a broad range of ketone substrates are suitable (even aliphatic ketones), either enantiomeric form of the a-chiral amine product can be produced, and the process has been demonstrated on a 20 g scale. The method is compatible with acetonides, ethers, silyl ethers, bulky esters, secondary amides, tertiary amides, carbamates, urethanes, etc. With these beneficial qualities noted, the method suffers when non-branched 2-alkanones are used (product des <75%). In these cases, HCl salt formation allows further enrichment via crystallization, alternatively stoichiometric Yb(OAc)3 can be used during the reductive amination to allow enhanced de. Both of these solutions require additional processing time and/or cost and require consideration before scale-up. 

A variety of vegetable oils have been directly used to obtain many industrially important paints and coatings. " However, vegetable oils alone cannot meet the film properties required for many applications and a number of approaches for modification of the oils are reported in the literature. These include the formation of functional groups such as ester, amide, oxirane, urethane and ester-amide, with an increase in molecular weight which will be discussed in subsequent chapters. 

Formation of vinylogous amides and urethanes by alkylation of secondary or tertiary thioamides with an electophilic agent followed by elimination of sulfur ... 

A related enamine alkylation is seen in the rearrangement of an ethylene imine vinylogous amide, which was heated with sodium iodide in diglyme. The presumed internal enamine alkylation constitutes a critical step in an oxocrinane synthesis (265). Use of an ethylene imine urethane for alkylation of an enamine and formation of the hexahydroindole system has also been reported (266). 

When the enolate of an ,) - or a /j,y-unsatunited amide is used, it can react in an a or in a y fashion with a,/i-unsaturated esters, however, in most cases only a-selectivity is observed. Using l-(l-oxo-2-butenyl)pyrrolidine and lithium diisopropylamide at — 78 °C in a THF/HM-I A mixture (1 1), high. syn-selective formation of 3-alkyl-5-oxo-5-(l-pyrrolidinyl)-4-vinylpen-tanoates is achieved78,381 382. Related syn- or anti-selective additions of a vinylogous urethane also are known79. 

Among the different chemical reactions usable to synthesize polymeric materials by step polymerisation are esterification, amidation, nucleophilic aromatic substitution and urethane (carbamate) formation. Polymerisation... 

Many of the common condensation polymers are listed in Table 1-1. In all instances the polymerization reactions shown are those proceeding by the step polymerization mechanism. This chapter will consider the characteristics of step polymerization in detail. The synthesis of condensation polymers by ring-opening polymerization will be subsequently treated in Chap. 7. A number of different chemical reactions may be used to synthesize polymeric materials by step polymerization. These include esterification, amidation, the formation of urethanes, aromatic substitution, and others. Polymerization usually proceeds by the reactions between two different functional groups, for example, hydroxyl and carboxyl groups, or isocyanate and hydroxyl groups. 

Reaction of the imidazole (7-4) with the benzofuran derivative (6-7) leads to the displacement of the benzylic halogen and the formation of the alkylation product (8-1). Treatment of that intermediate with trifluoroacetic acid breaks open the urethane to afford the corresponding free amine. This is allowed to react with ttiflic anhydride to afford the trifluoromethyl sulfonamide (8-2). The ester group on the imdidazole is then saponified, and the newly formed acid is reacted with carbonyl diimidazole. Reaction with ammonia converts the activated carboxyl group to the amide. There is thus obtained the angiotensin antagonist saprisartan (8-3) [6]. 

Incorporation of a piperazine function on the heterocyclic ring leads to a compound in which bronchodilator activity predominates. Treatment of the amino-amide (73-1) with trimethyl orthoformate provides the additional carbon atom for the formation of the quinazolone ring in (73-2). Reaction with phosphoms oxychloride in effect converts the ring to its aromatic form (73-3) by locking in the former amide as an enol chloride. Displacement of the halogen with the isobutyryl urethane (73-4) from piperazine affords piquizil (73-5) [82]. 

Other macromolecules are formed by condensing their monomers to form a repeat functional group (e.g., esters, amides, ethers) interspersed by alkyl chains, aromatic rings, or combinations of both. These condensations are characterized frequently, although not always by the loss of some by product (e.g., water, alcohol). The methods of formation of these polymers are far more varied than those of addition polymers. Examples of condensation polymers are (a) poly(esters), (b) poly(urethanes), (c) poly (carbonate), and (d) polyphenylene oxide). 

Dicarboxylic acid halogen amides, their salts and use in crosslinking of cellulose fibers thru urethane formation 5 D1202... 

The main problem a peptide chemist has to tackle with CMetrasubstituted a-amino acids is their rather poor reactivity in peptide-bond formation due to steric hindrance at the a-carbon. In addition, during the activation process of the carboxylic function of peptides and urethane or amide N-protected derivatives, an intramolecular reaction leading to the oxazoI -5 (4 //) -on e heterocyclic skeleton is greatly favored by the gem-dialkyl effect (Scheme... 

The formation of isocyanurates in the presence of polyols occurs via intermediate allophanate formation, i.e, die urethane group acts as a cocatalyst in the dimerization reaction. By combining cyclotrimeiization with polyurethane formation, processibility is improved, and the friability of the derived foams is reduced. Modification of cellular polymers by incorporating amide, imide, oxazolidinone, or carbodiimide groups has been attempted but only the urethane-modified isocyanurate foams are produced in the 1990s. PUIR foams often do not require added fire retardants to meet most regulatory requirements. A typical PUIR foam formulation is shown in Table 2. 

The polyurethane (PU) can be considered an environment-friendly material because the urethane bond resembles the amide bond, which implies possible biodegradability. It can be used in various elastomer formulations, paints, adhesives for polymers and glass, and artificial leather as well as in biomedical and cosmetic fields. Polyurethane spheres were prepared from 20/40% of PU prepolymer solution in xylene [91]. PU droplets were formed in water with the SPG membrane of different pore size (1.5-9.5 pm) and then polymerized to form the final microspheres. Finally, spherical and solid PU particles of 5 pm were obtained after the removal of the solvent. In another study, Ma et al. reported the formation of uniform polyurethane-vinylpolymer (PUU-VP) hybrid microspheres of about 20 pm, prepared using SPG membranes and a subsequent radical suspension polymerization process [92], The prepolymers were solubilized in xylene and pressed through the SPG membrane into the continuous phase containing a stabilizer to form uniform droplets. The droplets were left for chain extension at room temperature for some hours with di- and triamines by suspension polymerization at 70 °C for 24h. Solid and spherical PU-VP hybrid particles with a smooth surface and a higher destructive strength were obtained. 

Interaction of 258 with anilines or five-membered nitrogen heterocycles produced 265 and 266 via an aminoalkylation . Bicyclic derivatives 267-271 with an aminal structure resulted from the interaction of 258 with amides, urethanes, imides, ureas, amines or hydrazines. Finally, 272 was formed with carbon acids and a reduction to 273 occurred with the sodium salt of formic acid " . It is not yet totally clear whether an iminium ion is involved in the formation of 259-273. The yields of isolated products varied from 45 to 95 %. 

Polycondensation at room temperature between two or more fast-reacting intermediates is becoming widely used because of its convenience and speed. The interfacial polycondensation system, in particular, which employs two immiscible liquids, is applicable to a wide voriety of chemical structures amides, urethanes, esters, sulfonates, sulfonamides, and ureas. Many products can be made at low temperature which could not be formed by melt methods because of their infusibility or thermal instability. The low temperature procedures are subject to the effect of many variables, but these are readily controlled and acceptable conditions for use with new polymers or intermediates can usually be found. The processes are readily scaled up in simple batch equipment or continuous reactors. Special areas of application are the direct formation of fibers from the reactants and polycondensation on fiber substrates. 

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