Diazonium ions, reduction

Hurley, B. L. and R. L. McCreery. Covalent bonding of organic molecules to Cu and A1 alloy 2024 T3 surfaces via diazonium ion reduction. J. Electrochem. Soc. 151, 2004 B252-B259. 

Purines, N-alkyl-N-phenyl-synthesis, 5, 576 Purines, alkylthio-hydrolysis, 5, 560 Mannich reaction, 5, 536 Michael addition reactions, 5, 536 Purines, S-alkylthio-hydrolysis, 5, 560 Purines, amino-alkylation, 5, 530, 551 IR spectra, 5, 518 reactions, 5, 551-553 with diazonium ions, 5, 538 reduction, 5, 541 UV spectra, 5, 517 Purines, N-amino-synthesis, 5, 595 Purines, aminohydroxy-hydrogenation, 5, 555 reactions, 5, 555 Purines, aminooxo-reactions, 5, 557 thiation, 5, 557 Purines, bromo-synthesis, 5, 557 Purines, chloro-synthesis, 5, 573 Purines, cyano-reactions, 5, 550 Purines, dialkoxy-rearrangement, 5, 558 Purines, diazoreactions, 5, 96 Purines, dioxo-alkylation, 5, 532 Purines, N-glycosyl-, 5, 536 Purines, halo-N-alkylation, 5, 529 hydrogenolysis, 5, 562 reactions, 5, 561-562, 564 with alkoxides, 5, 563 synthesis, 5, 556 Purines, hydrazino-reactions, 5, 553 Purines, hydroxyamino-reactions, 5, 556 Purines, 8-lithiotrimethylsilyl-nucleosides alkylation, 5, 537 Purines, N-methyl-magnetic circular dichroism, 5, 523 Purines, methylthio-bromination, 5, 559 Purines, nitro-reactions, 5, 550, 551 Purines, oxo-alkylation, 5, 532 amination, 5, 557 dipole moments, 5, 522 H NMR, 5, 512 pJfa, 5, 524 reactions, 5, 556-557 with diazonium ions, 5, 538 reduction, 5, 541 thiation, 5, 557 Purines, oxohydro-IR spectra, 5, 518 Purines, selenoxo-synthesis, 5, 597 Purines, thio-acylation, 5, 559 alkylation, 5, 559 Purines, thioxo-acetylation, 5, 559... 

Scaiano and Kim-Thuan (1983) searched without success for the electronic spectrum of the phenyl cation using laser techniques. Ambroz et al. (1980) photolysed solutions of three arenediazonium salts in a glass matrix of 3 M LiCl in 1 1 (v/v) water/acetone at 77 K. With 2,4,5-trimethoxybenzenediazonium hexafluorophos-phate Ambroz et al. observed two relatively weak absorption bands at 415 and 442 nm (no e-values given) and a reduction in the intensity of the 370 nm band of the diazonium ion. The absence of any ESR signals indicates that these new bands are not due to aryl radicals, but to the aryl cation in its triplet ground state. 

Xu and Li (1989) investigated H — CIDNP spectra of fifteen substituted benzene-diazonium ions during reduction with NaBH4. The spectra are consistent with a mechanism in which the first step is the addition of a hydride ion to the diazonium ion. The diazene formed (Ar - N2 - H) is assumed to dimerize and disproportionate into a radical pair [Ar-N-NH2 N = N — Ar] which loses one equivalent of N2 yielding [Ar—N —NH2 Ar] and recombines to give the diarylhydrazine. A proportion of the aryl radicals escape and form the hydro-de-diazoniation product. 

A comparison of the products from the four benzenediazonium salts makes it clear that an increase in the electrophilicity of the diazonium ion favors homolytic dediazoniation in borderline solvents. As discussed in Section 8.6, increased electrophilicity is accompanied by an increase in the reduction potential (Ei/2), which is a measure of the tendency to add an electron and form an arenediazenyl radical (Ar-N ). 

The first step involves a reduction of the diazonium ion by the cuprous ion, which results in the formation of an aryl radical. In the second step, the aryl radical abstracts halogen from cupric chloride, reducing it. The CuX compound is regenerated and is thus a true catalyst. 

Aryl diazonium ions are converted to iodides in high yield by reaction with iodide salts. This reaction is initiated by reduction of the diazonium ion by iodide. The aryl radical then abstracts iodine from either I2 or I3. A chain mechanism then proceeds... 

Scheme 11.6 gives some examples of the various substitution reactions of aryl diazonium ions. Entries 1 to 6 are examples of reductive dediazonization. Entry 1 is an older procedure that uses hydrogen abstraction from ethanol for reduction. Entry 2 involves reduction by hypophosphorous acid. Entry 3 illustrates use of copper catalysis in conjunction with hypophosphorous acid. Entries 4 and 5 are DMF-mediated reductions, with ferrous catalysis in the latter case. Entry 6 involves reduction by NaBH4. 

Meerwein Arylation Reactions. Aryl diazonium ions can also be used to form certain types of carbon-carbon bonds. The copper-catalyzed reaction of diazonium ions with conjugated alkenes results in arylation of the alkene, known as the Meerwein arylation reaction.114 The reaction sequence is initiated by reduction of the diazonium ion by Cu(I). The aryl radical adds to the alkene to give a new (3-aryl radical. The final step is a ligand transfer that takes place in the copper coordination sphere. An alternative course is oxidation-deprotonation, which gives a styrene derivative. 

Reduction of aryl diazonium ions by Ti(III) in the presence of a,(3-unsaturated ketones and aldehydes leads to (3-arylation and formation of the saturated ketone or aldehyde. The early steps in this reaction parallel the copper-catalyzed reaction. However, rather than being oxidized, the radical formed by the addition step is reduced by Ti(III).116... 

Scheme 11.7 illustrates some arylation of alkenes by diazonium ions. Entries 1 to 4 are typical conditions. Entry 5 illustrates generation of the diazonium ion under in situ conditions. Entry 6 is an example of the reductive conditions using Ti(III). 

The phenanthrene 1,2- and 3,4-diones are synthetically accessible from the related 8 phenols. Oxidation of 2-phenanthrol with either Fremy s salt ((KS0 )2N0) or phenylseleninic anhydride gave phenanthrene 1,2-dione directly (55). Unexpectedly, oxidation of 3-phenanthrol with (KSOg NO yielded 2,2-dihydroxybenz(e)indan-l,3-d-ione (Figure 10). However, phenanthrene 3,4-dione was readily obtained from 3-phenanthrol by Fieser s method entailing diazonium coupling, reduction, and oxidation of the resulting 4-amino-3-phen-anthrol with chromic acid (56). 

Diazotization Diazonium ion decomposition gives a phenol in water and reduction in SDS Abe etal., 1983... 

CARBAZONES, see CARBAZIDES CARBOHYDRATES and SUGARS CARBOXYLIC ACIDS, see ACIDS, CARBOXYLIC CATALYTIC HYDROGEN-ION REDUCTION DEUTERATED COMPOUNDS, see ISOTOPES D IAZ0 COMPOUNDS DIAZONIUM SALTS ESTERS, CARBOXYLIC... 

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