Addition adducts

Zirconium tetraiodide is the least thermally stable zirconium tetrahaUde. At 1400°C, it disproportionates to Zr metal and iodine vapor. This behavior is utilized in the van Arkel-de Boer process to refine zirconium. As with the tetrachloride and tetrabromide, the tetraiodide forms additional adducts with gaseous ammonia which, upon heating, decompose through several steps ending with zirconium nitride. 

Zirconium monochloride reacts with sodium ethoxide to form additional adducts which hydrolyze in water. The monochloride does not react with benzene in a Friedel-Crafts reaction, and does not enter into intercalation reactions similar to those of zirconium disulfide. Both monohaUdes add hydrogen reversibly up to a limiting composition of ZrXH (131). 

In contrast, tertiary amines do not possess a proton to transfer, and the reaction of the Michael-type addition adduct with ECA can only initiate polymerization to form high molecular weight adhesive polymer, as shown earlier in Scheme 1. 

These amines gave, with methyl propiolate, products of Michael mono- and bis-addition. Adducts underwent further reaction leading to triazolo[4,5-/]quinolones 181, after retro Diels-Alder reaction and acetylene elimination to its methoxycar-... 

The monolithium salt of 4-hydroxy-4-(phenylethynyl)-2.5-cyclohexadienone (12), prepared in situ by the addition of lithium acetylide to /7-benzoquinone, was treated with methylmagnesium chloride in l HF-TMEDA or in THF —DMPU. The syn-, 4-addition adduct 13, derived from intramolecular delivery of the carbon nucleophile by the hydroxy oxygen, as well as the <7s-1,4-diol 14, obtained via intermolecular 1,2-addition, were obtained in varying amounts depending on the conditions. The selectivity on 1,4- to 1,2-addition increased by the addition of cation chelating agents such as DMPU, TMEDA, and 15-crown-5. Although the 1,4 to 1,2... 

Treatment of the olefin 49 with Zeise s dimer leads to the chloroplatination complex 50 [26], The addition adduct 50 is hydrogenated stereospecifically to the trans-disubstituted chlorocyclohexane 51. The insertion of carbon monoxide into 50, in the presence of methanol, yields the ester 52 stereoselectively. 

Subsequently, Westcott et al. reported the isolation of the oxidative addition adduct with the triisopropylphosphine derivative and its characterization by X-ray crystallography.7... 

An extensive range of compounds with homonuclear or heteronuclear single or double bonds between As, Sb, or Bi is known. They include the simple tetraorganodimetallic species, R2MMR2, double bonded species RM=MR, linear tri- and tetra-metallated species, and mono- or polycyclic compounds. In addition, adducts with coordinative metal-metal bonds are known.44-46 463 Examples for cationic species with Sb-Sb bonds are Me2SbSbMe2+ and... 

In addition, adducts of the surfactant molecule with two cations leading to doubly charged species were detected (m/z 183, 191, 199.5 and 211 Table 2.13.1). While the ammonium ions arose from ammonia added to the eluent for pH adjustment, the Na+ and K+ ions were assumed to originate from impurities in the solvents and the technical surfactant used. Cleavage of the bond between the methylene group... 

The most stable O2 addition adduct below T = 1250 K is 6-peroxyoxepinone (route A in Fig. 12), which can cyclize to form a 1,4-peroxy intermediate which subsequently releases CO2 to form a 5-oxopentanalyl radical. This species can cyclize and fragment, yielding formyl radical, furan, and carbon dioxide. Above T = 1250 K, the... 

Figure 4.6 Chemical shifts for the bridgehead C atoms and the methylene H-atoms and coupling constants j(CH) for the methano bridge C atoms in H2 for isomers 113a and 113b. The corresponding C atoms resonate in the region between 130 and 150 ppm together with all other sp -carbons of the fullerene sphere. For the 1,6-addition adduct of with (p-methoxy-phenyl)diazomethane, the peak position of the bridgehead C atoms was found by HETCOR analysis to be 138.65 ppm [110. ...

In 1994, Mansuy and coworkers found that a simple ammonium salt, like ammonium acetate alone, is a very efficient cocatalyst for the metalloporphyrin-catalyzed epoxidation of simple alkenes by hydrogen peroxide ". Bases like sodium carbonate, sodium acetate or tetrabutylammonium hydroxide turned out to promote the porphyrin-catalyzed epoxidation without any other additive. Adducts of hydrogen peroxide (with Na2C03, urea, MesNO, PhsPO), which turned out to be particularly useful for reactions in which the concentration of H2O2 in solution needs to be controlled at a fixed level, have been employed by Johnstone and coworkers. 

Despite the reduction in symmetry, no additional bands have ever been unambiguously assigned to internal fullerene active vibrations. For multiple addition adducts, the severe disruption to the cage structure results in a markedly different spectrum. 

Oxamborolidenes. There are noteworthy advances in the design, synthesis, and study of amino acid-derived oxazaborolidene complexes as catalysts for the Mukaiyama aldol addition. Corey has documented the use of complex 1 prepared from A-tosyl (S)-tryptophan in enantioselective Mukaiyama aldol addition reactions [5]. The addition of aryl or alkyl methyl ketones 2a-b proceeded with aromatic as well as aliphatic aldehydes, giving adducts in 56-100% yields and up to 93% ee (Scheme 8B2.1, Table 8B2.1). The use of 1-trimethylsilyloxycyclopentene 3 as well as dienolsilane 4 has been examined. Thus, for example, the cyclopentanone adduct with benzaldehyde 5 (R = Ph) was isolated as a 94 6 mixture of diastereomers favoring the syn diastereomer, which was formed with 92% ee, Dienolate adducts 6 were isolated with up to 82% ee it is important that these were shown to afford the corresponding dihydropyrones upon treatment with trifuoroacetic acid. Thus this process not only allows access to aldol addition adducts, but also the products of hetero Diels-Alder cycloaddition reactions. 

Isocyanides, formal divalent carbon functionalities, are ideal candidates for the development of MCRs. Their reaction with carbonyls and imines, through an a-addition process, generates a zwitterionic intermediate, which is then trapped by a nucleophile. The resulting double a-addition adduct is unstable and rapidly undergoes the Mumm rearrangement to afford the final product (Scheme 12.32). The venerable three-component Passerini reaction is the first MCR based on this type of reaction process [116]. It addresses the formation of a-acyloxycarboxamides, which constitute a class of very versatile synthons in organic chemistry. In the present context, this reaction was utilized by Schmidt and collaborators for the elaboration of intermediate 234 [117], a key fragment for the synthesis of the prolyl endopeptidase inhibitor Eurystatin A 231 (Scheme 12.33) [118]. 

The initial a-addition adduct from the reaction of methyl (S)-2-isocyano-4-methylpentanoate 232 and protected (S)-alaninal 233 further reacted with benzoic acid to furnish 234 as a diastereomeric mixture. The stereochemistry of the resulting benzoyl-protected alcohol was inconsequent since the latter functionality is oxidized during the course of the synthesis using pyridinium dichromate to afford the a-oxoamide in the final target. In general, however, in isocyanide MCRs the control of the newly created stereogenic center is problematic and separation of diastereomeric mixtures cannot be avoided. A recent report by Denmark and Fan on a catalytic asymmetric variant of this reaction therefore represents an interesting development [119]. 

The Michael addition of nitroalkanes to a,f -unsaturated enones, catalysed by the novel chiral imidazolidine-2-yltetrazole (151), has been investigated. The new, more soluble organocatalyst decreases reaction times and improves enantioselectivities com- pared with other catalysts. The Michael addition adducts were obtained with up to 92% ee.179... 

The foregoing two sections revealed that lanthanide centers like to expand their coordination sphere by additional adduct formation despite the presence of very bulky ligands such as tritox or OC6H2tBu3-2,4,6. With regard to headwords such as sublimation and homogeneity , these neutral co-ligands are a nuisance and undesired. For example, upon thermal treatment, they often separate off and dimerization occurs along with the formation of a less volatile species [29,78],... 

The rosette of Scheme 11.7 shows the endoper oxidation of the corresponding diene compounds in Scheme 11.6. In one case, a solvent addition adduct was formed. 

The condensation of aminobenzotriazoles with DMAD gave (Z)-conjugate addition adducts which underwent ring closure in boiling Dowtherm to give triazolo[4,5-/]quinolinones (100) (Equation (57)) <93H(36)259>. The quinolinone form of the product (100) is supported by 13C NMR spectroscopic evidence. It was found that ring closure to the tricycle fails in the absence of an N-methyl substituent retro-Michael addition takes place instead. 

Regioselective addition of 2-methoxyfuran and 2-trimethylsilyloxyfuran to chromium(O) alkynylcarbene complexes furnished interesting dienyne and dienediyne carboxylates <07AGE2610>. The reaction likely proceeded through a formal vinylogous Michael addition adduct, as illustrated in the following example. 

In a different approach, chiral auxiliaries have been widely used in Reissert-type chemistry to provide practical access to enantiopure addition adducts. For example, the stereoselective addition of cyanide to isoquinoline or quinoline with a modified... 

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