Chemical bond imine

On the basis of the same principle, we developed a three-component synthesis of macrocycles starting from azido amide (46), aldehyde (47) and a-isocyanoaceta-mide (48) (the cx-isocyanoacetamides are easily available, see [84—86]) bearing a terminal triple bond (Scheme 11) [87]. The sequence is initiated by a nucleophilic addition of isonitrile carbon to the in situ generated imine 50 led to the nitrilium intermediate 51, which was in turn trapped by the amide oxygen to afford oxazole 52 (selected examples [88-94]). The oxazole 52, although isolable, was in situ converted to macrocycle 51 by an intramolecular [3+2] cycloaddition upon addition of Cul and diisopropylethylamine (DIPEA). In this MCR, the azido and alkyne functions were not directly involved in the three-component construction of oxazole, but reacted intramolecularly leading to macrocycle once the oxazole (52) was built up. The reaction created five chemical bonds with concurrent formation of one macrocycle, one oxazole and one triazole (Scheme 15). 

Fourre et al found that their ELF-based topological description of the chemical bond provides a deeper insight into the bonding evolution upon excitation, ionization, and electron attachment in carbonyl and imine compounds than the classical MO point of view. The changes occurring in the valence basin... 

Besides these chemically bonded residues, it is possible to form stationary phases for ion-exchange chromatography based on cellulose by impregnation. Examples of this are the polyethylene imine (PEI) and the polyphosphate (Poly-P) celluloses. The cellulose exchangers discussed here have to be distinguished based on their use for an anion- or cation-exchange mechanism. Suitable for the... 

Isocyanide has been widely utilized as a key reagent in organic synthesis. Besides, the insertion of isocyanides into M-C bonds is one of the powerful means for carbon chain construction [16-34]. Insertion of isocyanide into M-C bonds afforded / -iminoacyl-metal intermediates, such as / -iminoacyl-Zr complexes [19-27], which can be conveniently converted to one-carbon elongated products such as imines, aldehydes, or nitriles via various chemical bond cleavage including Zr-C, C=N, and N-R bonds (Scheme 2.8) [29-32]. / -Iminoacyl-Zr complexes... 

Many biological processes involve an associa tion between two species in a step prior to some subsequent transformation This asso ciation can take many forms It can be a weak associ ation of the attractive van der Waals type or a stronger interaction such as a hydrogen bond It can be an electrostatic attraction between a positively charged atom of one molecule and a negatively charged atom of another Covalent bond formation between two species of complementary chemical re activity represents an extreme kind of association It often occurs in biological processes in which aide hydes or ketones react with amines via imine inter mediates... 

A mechanistic rationale for the observed cw-selectivity has been proposed based on preorganisation of the Breslow-type intermediate and imine through hydrogen bonding 253, with an aza-benzoin oxy-Cope process proposed. Reaction via a boat transition state delivers the observed cw-stereochemistry of the product (Scheme 12.57). Related work by Nair and co-workers (using enones 42 in place of a,P-unsaturated sulfonylimines 251, see Section 12.2.2) generates P-lactones 43 with fran -ring substituents, while the P-lactam products 252 possess a cw-stereo-chemical relationship. 

Because organophosphorus compounds are important in the chemical industry and in biology, many methods have been developed for their synthesis [1]. This chapter reviews the formation of phosphorus-carbon (P-C) bonds by the metal-catalyzed addition of phosphorus-hydrogen (P-H) bonds to unsaturated substrates, such as alkenes, alkynes, aldehydes, and imines. Section 5.2 covers reactions of P(lll) substrates (hydrophosphination), and Section 5.3 describes P(V) chemistry (hydrophosphorylation, hydrophosphinylation, hydrophosphonylation). Scheme 5-1 shows some examples of these catalytic reactions. 

T. Deuterium isotope effects on 13 C chemical shifts In the studies of proton transfer equilibrium of Schiff bases, the most informative are deuterium isotope effects measured for carbons bonded with proton donor groups (C-2 or C-7 for gossypol derivatives). For imines in which... 

The values of the 15N CP MAS chemical shift of Lys296 nitrogen bonded to retinal via the —C=N bond ( Schiff base) was equal to 155.4 ppm for rhodopsin and 282.8 ppm for metarhodopsin (relative to 5.6 M aqueous NH4C1).70 The results proved the imine bond polarisation, which facilitates Schiff base hydrolysis. The comparison between chemical shifts for metarhodopsin and model compounds suggested that Schiff base linkage of the all-frans retinal chromophore in Metall is in a polar environment. 

This chapter deals with [2 + 2]cycloadditions of various chromophors to an olefinic double bond with formation of a four-membered ring, with reactions proceeding as well in an intermolecular as in an intramolecular pattern. Due to the variety of the starting materials available (ketones, enones, olefins, imines, thioketones, etc.. . .), due to the diversity of products obtained, and last but not least, due to the fact that cyclobutanes and oxetanes are not accessible by such a simple one-step transformation in a non-photo-chemical reaction, the [2+2]photocycloaddition has become equivalent to the (thermal) Diels-Alder reaction in importance as for ring construction in organic synthesis. 

Organic dye nanoparticles of DHIA and DHBIA (the chemical structures are shown in Fig. 1) have been synthesized in THF/water mixed solvent by a reprecipitation method [32]. These dye molecules possess a 2-(2-hydroxyphenyl) benzothiazole (HBT) unit, which is known to be more stable as an enol imine form in the ground state and as a keto amine form in the excited state [32, 33] (Fig. 6). The nanoparticles exhibited the AIEE phenomenon mainly due to a restricted intramolecular motion, that is, impediment to free rotation of two end-substituted HBT units around single bonds. It is interesting to note that the... 

The kinetics and mechanism of pyrrole pyrolysis were investigated by ab initio quantum-chemical calculations. It was revealed that pyrrole undergoes tautomerization to form 2H- and 37/-pyrroles prior to any thermal decomposition. It has been shown that the major product, HCN, arises from a hydrogen migration in pyrrole to form a cyclic carbene with the NH bond intact. Ring scission of the carbene leads to an allenic imine of HCN and propyne which is the lowest energy pathway. The 277-pyrrole... 

The reaction of an amino group with an aldehyde or ketone leads to an imine, which, as we have just seen with aldolase, provides a splendid example of how to bond a carbonyl substrate to an enzyme, and yet maintain its chemical reactivity in terms of enolate anion chemistry. Another type of covalent interaction is quite commonly encountered, and this exploits the thiol group of cysteine. Thiols are more acidic than... 

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