Isocyanates, amino functionalization using

Related methods may be used to introduce amino functions. For example, thiocyanate 237, made from the 4,6-dimesylate, rearranges to the isothiocyanate 238,225 and 3,4-unsaturated 2-cyanates, easily made in situ from the corresponding carbamates, afford the A-bonded 4-isocyanates of the 2-enes.229 From both types of rearranged products aminodeoxy sugars may be accessed, and in this way perosamine peracetate (239) can be synthesized from the cyanate of a 3,4-unsaturated 2-ol, which is thermally rearranged prior to dihydroxylation and acetylation.229... 

Forosamine is an amino sugar component of the antibiotic Lepicidin. Since Le-picidin is sensitive to acid and catalytic hydrogenation, an Fmoc group was selected to protect the amino function. A rather unconventional method was used to introduce it [Scheme 8.94].230 A Curtius rearrangement on the acyl azide derived from carboxylic acid 94.1 proceeded with retention of configuration to give the isocyanate intermediate 94.2 that was trapped with 9-fluorenylmethanol to afford the N-Fmoc derivative 94J in 72% yield. 

Despite the transformation of a certain number of amino groups into urea groups, the qualitative shape of the zeta-potential plots as a function of pH is not changed significantly. That indicates that PVFA-co-PVAm can be used as a precursor polymer for the gradual functionalization of silica particles and other Bronsted-acidic surfaces with amino functionality. Chemical reactions of PVFA-co-PVAm/silica particles with isocyanates or other electrophilic reagents offer a wide field of applications, because of the simple experimental procedure this material combination seems promising for the construction of tailor-made polyelectrolyte networks on Bronsted-acidic surfaces or for other multicomponent systems. 

The alternative [2 + 2] cycloaddition route to azetidinones, using chloro-sulphonyl isocyanate and functionalized alkenes, has been further used in syntheses of /8-lactam antibiotics. Asymmetric induction in the formation of /3-amino-aa-dimethyl-/8-phenylpropionic acid has been achieved, using a Reformatsky reagent and a chiral Schifif base, the reaction proceeding through a /3-lactam intermediate. ... 

Thermosetting (crosslinking) acrylics normally require a crossUnker to be present. Their actual cure behaviour is dependent upon the pendant (side chain) functionality of the copolymerised co-monomers. Acrylamide will crosslink with itself, epoxy or amino resins, whilst amino or melamine crosslinkers will react with hydroxyl or acid groups. Isocyanates can react with hydroxyl groups at room temperature. To reduce the hazards of isocyanates and the inconvenience of two pack systems, blocked isocyanates can be used. At elevated temperatures used for stoving they can unblock generating an alcohol and an isocyanate which will react with any hydroxyl or acid groups on the acryUc resin. 

Nitrocellulose based lacquers often contain short or medium oil alkyds to improve flexibiUty and adhesion. The most commonly used are short oil non drying alkyds. Amino resins or urethane resins with residual isocyanate functional groups may be added to cross-link the coating film for improved solvent and chemical resistance. The principal appHcations are furniture coatings, top lacquer for printed paper, and automotive refinishing primers. 

Reaction with Phosgene. This reaction of amino acid esters is used for preparing the corresponding isocyanates, especially lysine diisocyanate [4460-02-0] (LDI). LDI is a valuable nonyellowing isocyanate with a functional side group for incorporation in polyurethanes. 

Urethane sealants have good inherent adhesion to most substrates, but silane adhesion promoters are often used to improve this adhesion. Epoxy-, amino-, and mercapto-functional silanes are the most common because of their dual reactive nature. The silane end can react with surface hydroxyls the epoxy, amino, or mercapto end can react with the isocyanate. 

In order to investigate dendrimers of a different nature [230], Bradley described the synthesis and transfection efficiency of polyamidourea dendrimers synthesised from isocyanate-containing AB3 monomers [231-234]. The use of this kind of tris-branched building block was addressed to enhance dendrimer synthesis by replacement of the 1,4-addition step typical of PAMAM synthesis and to a rapid increase in terminal functionality. The dendritic structures were synthesised using a divergent, microwave-assisted, solid-phase approach with the dendrimers assembled on polystyrene resin via an acid labile linker (see Fig. 26). In particular, a G3.0 polyamidourea bis-dendron with the peripheral amino groups conjugated to L-lysine residues demonstrated remarkable transfection abilities [234],... 

There are several types of chiral derivatizing reagents commonly used depending on the functional group involved. For amines, the formation of an amide from reaction with an acyl halide [147,148], chloroformate reaction to form a carbamate [149], and reaction with isocyanate to form the corresponding urea are common reactions [150]. Carboxyl groups can be effectively esterified with chiral alcohols [151-153]. Isocynates have been used as reagents for enantiomer separation of amino acids, iV-methylamino acids, and 3-hydroxy acids [154]. In addition to the above-mentioned reactions, many others have been used in the formation of derivatives for use on a variety of packed and capillary columns. For a more comprehensive list, refer to References 155-159. 

When primary aliphatic isocyanates that show the lowest reactivity compared to secondary or aromatic isocyanates are used in combination with hydrophilic (pre-) polymers, crosslinking may be performed in aqueous solution without the use of additional crosslinkers. At neutral pH, hydrolysis of isocyanates to carbaminic acid with subsequent decarboxylation yields amines. These amines react much more rapidly than water with isocyanates, resulting in crosslinking if the functionality per macromolecule is more than two [43], This crosslinking reaction can be quenched by adjustment of the pH value. At pH values above 10, carbamate formation is faster than decarboxylation, whereas at pH values below 3 an almost quantitative protonation of the formed amino groups results in the formation of ammonium. In both cases, chemical crosslinking is prevented. 

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