Adduct-forming reactions

Adduct-forming reactions of Mg with alkanes, aUcenes and other... 

Adduct-forming reactions of Mg+ with aikanes, aikenes and other unsaturated species... 

The kinetic approach confirmed our presumption that the optically active 1-phenylethanol arised from the hydrogenolytic cleavage of the C-N bond of the adduct of (S)-proline and acetophenone. The reasons for the relatively low enantioselectivities are (i) the low diastereoselectivity 100[nu-(l-nu)]=32% with the presumption of retention in the hydrogenolysis of the adduct forming reaction and (ii) the ratio of competitive reactions namely the hydrogenation of the free acetophenone and that of the adduct. 

Sulfite ions, too, show high reactivity in adduct-forming reactions. With TNB, 2,4, 6-trinitroanisole and V-substituted picramide adducts with 1 1 and 2 1 stoichiometries may be formed by reaction at unsubstituted ring positions. Measurements in water and DMSO show that formation of 2 1 adducts (62) is favored in water that will solvate the localized negative charges [126]. 

Sulfamation is the formation (245) of a nitrogen sulfur(VI) bond by the reaction of an amine and sulfur trioxide, or one of the many adduct forms of SO. Heating an amine with sulfamic acid is an alternative method. A practical example of sulfamation is the artificial sweetener sodium cyclohexylsulfamate [139-05-9] produced from the reaction of cyclohexylamine and sulfur trioxide (246,247) (see Sweeteners). Sulfamic acid is prepared from urea and oleum (248). Whereas sulfamation is not gready used commercially, sulfamic acid has various appHcations (see SuLFAMiC ACID AND SULFAMATES) (249—253). 

Several methods were reported for the analysis of histamine, but the fluorimetric determination with o-phthaldialdehyde (OPA) the most widely used. It was shown that adducts, formed in the reaction of histamine with OPA in the presence of reducing agent, is more stable and gives high relative fluorescence intensity. The influences of different tiols on the fluorimeric determination histamine with OPA have been investigated. 

Tliere is ample NMR evidence for the existence of the covalent 4-amino-dinitro compounds (87a/ 87b) and (90b) with liquid ammonia (see Chapter 5). In the cases of 87c or 87d, besides the covalent 4-amino-temperature dependent (85JHC761). For example, when 87c was dissolved in liquid ammonia at -45°C the ratio of 4-amino-room temperature it changed to 40 60. However, 87d, when dissolved in liquid ammonia at -45°C, gave a mixture of 4- and 5-amino-[Pg.304]

Problem 14.5 J The 1,2 adduct and the 1,4 adduct formed by reaction of HBr with 1,3-butadiene are in equilibrium at 40 °C. Propose a mechanism by which the interconversion of products lakes place. 

When 2-lithio-2-(trimethylsilyl)-l,3-dithiane,9 formed by deprotonation of 9 with an alkyllithium base, is combined with iodide 8, the desired carbon-carbon bond forming reaction takes place smoothly and gives intermediate 7 in 70-80% yield (Scheme 2). Treatment of 7 with lithium diisopropylamide (LDA) results in the formation of a lactam enolate which is subsequently employed in an intermolecular aldol condensation with acetaldehyde (6). The union of intermediates 6 and 7 in this manner provides a 1 1 mixture of diastereomeric trans aldol adducts 16 and 17, epimeric at C-8, in 97 % total yield. Although stereochemical assignments could be made for both aldol isomers, the development of an alternative, more stereoselective route for the synthesis of the desired aldol adduct (16) was pursued. Thus, enolization of /Mactam 7 with LDA, as before, followed by acylation of the lactam enolate carbon atom with A-acetylimidazole, provides intermediate 18 in 82% yield. Alternatively, intermediate 18 could be prepared in 88% yield, through oxidation of the 1 1 mixture of diastereomeric aldol adducts 16 and 17 with trifluoroacetic anhydride (TFAA) in... 

Similar 2,3-adducts form with chlorine or bromine in carbon tetrachloride when the reactions are carried out with an iodine promotor and in the presence of light [57FES930 60LA(631)194], More polar solvents... 

The different possible adducts formed between mitomycin C and DNA have been isolated by degradation of DNA after in vitro alkylation/crosslinking reactions and structurally characterized. Monoadduct 21 (Scheme 11.3), derived from alkylation at C-l only [53], and monoadducts 22 [54] and 23 [55, 56] (derived from C-10 alkylation by 16 at N-7 or N-2 of guanine, respectively) have been isolated, together with bisadducts 24 [57] and 25 [58], derived from interstrand and intrastrand crosslinks, respectively, and adduct 26 [59], formed by addition of a molecule of water to C-10 instead of the second guanine. All of these adducts have also been isolated from DNA after in vivo crosslinking [60, 61]. 

The predominating onti-diastereomers of the primary adduct form an ( (-double bond on anti elimination and a (Z)-double bond on syn elimination, the latter proceeding frequently on warming of the reaction mixture to room temperature. 

Alkaline hydrolysis of the crude adduct formed with benzaldehyde, followed by treatment with diazomethane and column chromatography, affords methyl (2R,3S)-3-hydroxy-2-methyl-3-phenylpropanoate in 96% ee. Reduction of the crude products formed in the reactions with 2-inethylpropanal and 2,2-dimethylpropanal leads to the corresponding 1,3-diols with >96% ee. In both the hydrolysis and the reduction procedures, the chiral auxiliary reagent, 1,1,2-triphenyl-1,2-ethanediol, can be recovered and reused72. 

Incorporation of a chiral phosphane allowed resolution of the complex 6 which was obtained in enantiomerically pure form. Reaction of 6 with 2,2-dimethylpropanal provided the adduct 7 as the sole observable aldol product13. Oxidation of the metal center of 7 with ferric chloride induced decomplexation via reductive elimination, to provide the enantiomerically pure cy-clobutanone 8. 

Reaction of the chiral (45,5R)-oxazolidine 9. obtained from 3-pentanone and (-)-2-amino-l-phenylpropanol, with aldehydes gives predominantly a H -aldol adducts of high enantiomeric purity. The corresponding spn-adducts, formed in low enantiomeric excess, are isolated from the diaslereomeric mixture by chromatography 5. 

The Vilsmeier-Haack type adduct, formed by the reaction of oxalyl chloride with DMF can be also be employed for the activation of carboxylic acids, as shown in Fig. 8 [200]. 

If reaction time is kept short, however, the derivatization process can be intercepted at the mono-adduct form, which is sufficiently fluorescent for assay purposes. It should be noted that the fluorescence efficiencies of the CBI adducts are relatively insensitive to the water content of the solvent mixture (11,12) in contrast with earlier reports on the dansyl derivatives, which lose an order of magnitude of efficiency in aqueous-based solvent systems(9). 

The simplest type of Lewis acid-base reaction is the combination of a Lewis acid and a Lewis base to form a compound called an adduct. The reaction of ammonia and trimethyl boron is an example. A new bond forms between boron and nitrogen, with both electrons supplied by the lone pair of ammonia (see Figure 21-21. Forming an adduct with ammonia allows boron to use all of its valence orbitals to form covalent bonds. As this occurs, the geometry about the boron atom changes from trigonal planar to tetrahedral, and the hybrid description of the boron valence orbitals changes from s p lo s p ... 

B. Reactions.—This year has seen the publication of a number of papers on the reactions of olefins and acetylenes with phosphorus pentachloride, to produce new phosphorus-carbon bonds. An investigation into the structural requirements of trisubstituted olefins (40) undergoing the above reaction has shown that both steric and electronic factors are important, e.g. an adduct forms with (40 X = CH3) but no reaction occurs for (40 X = Ph). Further examples of the reactions of unsaturated ethers include the formation and decomposition of adducts from a-methoxystyrene... 

Although the path (a), which is the initiation stage of the catalytic reaction, was actually confirmed by a stoichiometric reaction, no direct evidence has been provided about paths (b)-(d). When the reaction was carried out by using PdCl2(PhCN)2 as a catalyst precursor, the Markovnikov adducts formed in situ isomerized into internal vinyl sulfide 14 (Eq. 7.10) [22]. 

The chemical adducts formed by reaction of aldehydes with lysine residues form highly immunogenic epitopes, and antibodies have been prepared specific for malondialdehyde- and 4-hydroxynonenal-conjugated LDL (Gonen et al., 1987 Yla-Herttuala et al., 1989 Jurgens et al., 1990). These antibodies cross-react with material in atherosclerotic lesions but not normal tissue, thus supporting the central role of lipid peroxidation in the patho nesis of atherosclerosis (Yla-Herttuala et al., 1989, 1991). 

Stone, K., Ksebati, M. and Marnett, L.J. (1990a). Identification of the adducts formed by reaction of malondialdehyde with adenosine. Chem. Res. Tox. 3, 33-38. 

The mechanism of conjugate addition reactions probably involves an initial complex between the cuprate and enone.51 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species, which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.52 Solvent molecules also affect the reactivity of the complex.53 The mechanism can be outlined as occurring in three steps. 

In contrast to the lability of certain dN adducts formed by the BHT metabolite above, amino acid and protein adducts formed by this metabolite were relatively stable.28,29 The thiol of cysteine reacted most rapidly in accord with its nucleophilic strength and was followed in reactivity by the a-amine common to all amino acids. This type of amine even reacted preferentially over the e-amine of lysine.28 In proteins, however, the e-amine of lysine and thiol of cysteine dominate reaction since the vast majority of a-amino groups are involved in peptide bonds. Other nucleophilic side chains such as the carboxylate of aspartate and glutamate and the imidazole of histidine may react as well, but their adducts are likely to be too labile to detect as suggested by the relative stability of QMs and the leaving group ability of the carboxylate and imidazole groups (see Section 9.2.3). 

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