Reactions with electrons

In a previous study [1], NF has been found to form with low or no kinetic energy in a dissociative capture process at zero electron energy, possibly by the process NF3 + e- NF 2F. Its resonance maximum was at 2.8 eV. The cluster ion NF3-F was identified in electron swarm experiments with a mixture of 0.04% NF3 in N2 using a drift tube mass spectrometer system [13]. 

Formation of positive ions. At an electron energy of 70 eV, NF3 gives the following ions In its mass spectrum [12]  

The formation of highly excited, long-lived ( 10 s) N and F atoms (Rydberg atoms) from NF3 during dissociative excitation by electron impact is described in [16]. 

Selective reduction of indole in the benzene ring can be achieved by treatment with lithium in liquid ammonia, which gives a mixture of the 4,7-dihydro and 4,5,6,7-tetrahydro derivatives. 

Birch reduction of indole with lithium metal in THF in the presence of trimethylsilyl chloride followed by oxidation with p-benzoquinone gave 1,4-bis(trimethylsilyl)indole (298). This is readily converted in two steps into l-acetyl-4-trimethylsilylindole. Friedel-Crafts acylation of the latter compound in the presence of aluminum chloride yields the corresponding 4-acylindole (299) (82CC636). 

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Ozone can be destroyed thermally, by electron impact, by reaction with oxygen atoms, and by reaction with electronically and vibrationaHy excited oxygen molecules (90). Rate constants for these reactions are given ia References 11 and 93. Processes involving ions such as 0/, 0/, 0 , 0 , and 0/ are of minor importance. The reaction O3 + 0( P) — 2 O2, is exothermic and can contribute significantly to heat evolution. Efftcientiy cooled ozone generators with typical short residence times (seconds) can operate near ambient temperature where thermal decomposition is small. 

The Bart reaction is successful with a wide variety of aromatic and heterocycHc amines. A variation in which an aromatic amine, in the presence of arsenic trichloride, is dia2oti2ed in an organic solvent (the ScheUer reaction) has also found wide appHcation. Both arsonic and arsinic acids can be prepared by the ScheUer reaction which often gives better yields than the Bart reaction with electron-attracting substituents on the aromatic ring. For the commercial preparation of 4-aminophenylarsonic acid [98-50-0] (arsaniUc acid), C HgAsNO, and 4-hydroxyphenylarsonic acid [98-14-6] C H AsO, the Bnchamp reaction is used ... 

Reactions with electrons and surface reactions (Section 5.05.3.6)... 

Seven procedures descnbe preparation of important synthesis intermediates A two-step procedure gives 2-(HYDROXYMETHYL)ALLYLTRIMETH-YLSILANE, a versatile bifunctional reagent As the acetate, it can be converted to a tnmethylenemethane-palladium complex (in situ) which undergoes [3 -(- 2] annulation reactions with electron-deficient alkenes A preparation of halide-free METHYLLITHIUM is included because the presence of lithium halide in the reagent sometimes complicates the analysis and use of methyllithium Commercial samples invariably contain a full molar equivalent of bromide or iodide AZLLENE IS a fundamental compound in organic chemistry, the preparation... 

Fluorine-substituted heterodienes are particularly prone to inverse electron demand Diels-Alder reactions with electron-rich dienophiles, as can be seen from the examples in equations 94-97 [113, 114, 115, 116, 117]... 

Arenediazonium ions 1 can undergo a coupling reaction with electron-rich aromatic compounds 2 like aryl amines and phenols to yield azo compounds 3. The substitution reaction at the aromatic system 2 usually takes place para to the activating group probably for steric reasons. If the para position is already occupied by a substituent, the new substitution takes place ortho to the activating group. 

Reaction with Electron-Rich Siloxy-Substituted 1,3-Dienes. 79... 

The regioselectivity observed in these reactions can be correlated with the resonance structure shown in Fig. 2. The reaction with electron-rich or electron-poor alkynes leads to intermediates which are the expected on the basis of polarity matching. In Fig. 2 is represented the reaction with an ynone leading to a metalacycle intermediate (formal [4C+2S] cycloadduct) which produces the final products after a reductive elimination and subsequent isomerisation. Also, these reactions can proceed under photochemical conditions. Thus, Campos, Rodriguez et al. reported the cycloaddition reactions of iminocarbene complexes and alkynes [57,58], alkenes [57] and heteroatom-containing double bonds to give 2Ff-pyrrole, 1-pyrroline and triazoline derivatives, respectively [59]. 

Epoxidations of chiral allenamides lead to chiral nitrogen-stabilized oxyallyl catioins that undergo highly stereoselective (4 + 3) cycloaddition reactions with electron-rich dienes.6 These are the first examples of epoxidations of allenes, and the first examples of chiral nitrogen-stabilized oxyallyl cations. Further elaboration of the cycloadducts leads to interesting chiral amino alcohols that can be useful as ligands in asymmetric catalysis (Scheme 2). 

Reaction with Co2(CO)g 6.5.2.1 Reaction with electron pair bases 6.2.2.1... 

Reaction with electron pair bases CI5P 12 C215H)H(... 

The benzthiazole (62), an example of a stabilised 1-azabuta-1,3-diene, undergoes Inverse type Diels-Alder reactions with electron-rich dienophiles under extremely mild conditions. 

So far only Pd-based systems have been highlighted in this section however, the use of other metals such as Ni has clear economic advantages. In this regard, Chiu and co-workers have used a bis-carbene tetradentate ligand to catalyse the coupling of aryl bromides and chlorides with both electron rich and electron poor aromatic rings however, the reaction with electron poor aryl bromides lead to superior yields (Scheme 6.30) [113]. 

Conjugated heteropentalene mesomeric betaines are electron rich with high-energy HOMO and can be regarded as masked 1,3-dipolarophiles. Their main reactions are electrophilic substitution and cycloaddition reactions with electron-deficient 1,3-dipolarophiles, both were duly discussed in CHEC-II(1996) <1996CHEC-II(8)747>. 

Sulfonyl imides (78) are, like sulfenes, prepared by dehydrohalogenation of the corresponding sulfonyl chlorides (79) (usually called sulfamoyl chlorides). Like sulfenes, they take part in [2 + 2] and [4 + 2] cycloaddition reactions with electron-rich alkenes or with 1,3-dienes, yielding 1,2-thia-zetidine 1,1-dioxides (80)104 or dihydro-1,2-thiazines (81),105 respectively. 

Bagley and coworkers have described the preparation of primary thioamides by treatment of nitriles with ammonium sulfide in methanol solution (Scheme 6.139) [276], While the reactions with electron-deficient aromatic nitriles proceeded at room temperature, other aromatic and aliphatic nitriles required microwave heating at 80-130 °C for 15-30 min to furnish the thioamides in moderate to high yields. This protocol avoids the use of hydrogen sulfide gas under high pressure, proceeds in the absence of base, and usually provides thioamides without the need for chromatographic purification. 

Mukaiyama reaction (Lewis acid-catalyzed Michael reaction) with electron-poor olefins, ketals and acetals, and enones 32... 

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