Iodobenzenes reduction

Organotin compounds such as aryl-, alkenyl-, and alkynylstannanes are useful for the ketone synthesis by transmetallation of acylpalladium 529 and reductive elimination of 530 as shown[389-393]. Acetophenone (531) is obtained by the carbonylation of iodobenzene with Me4Sn. Diaryl ketones... 

Sodium cyclopentadienide, 41, 96 Sodium dichromate for oxidation of alkylarcncs to aromatic carboxylic acids, 43, 80 Sodium iodide, in conversion of 2,4-di-nitrochlorobenzene to 2,4-dinitro-iodobenzene, 40, 34 reduction of peroxide with, 41,... 

Hydrodehalogenations of chloro-, bromo-, and iodobenzene were carried out individually as well as in competitive reactions. When the reactions were carried out separately, the reduction of chlorobenzene closely paralleled that of bromobenzene, whereas the reduction of iodobenzene was slower. When they were allowed to react competitively, the reduction was highly selective, and the reaction was delayed, but iodobenzene reacted first followed by bromobenzene and then chlorobenzene. 

Porco s route to (—)-kinamycin C (3) began with 2,5-dihydroxybenzaldehyde (38), which was elaborated to the enone 35 by the sequence shown in Scheme 3.6. Regioselective bromination [25] followed by methylation and reduction of the aldehyde function afforded the primary alcohol 39. The alcohol 39 was dearomatized by treatment with bis(acetoxy)iodobenzene, to afford the quinone monoketal 41. Transketalization with 1,3-propanediol followed by silylation of the primary alcohol generated the silyl ether 42 in 72 % yield over three steps. 

Fig. 5 Electrochemical reduction of aryl halides showing the variation of the apparent transfer coefficient with the scan rate. iodobenzene, O bromobenzene, V 1-iodonaphthalene, O 4-methyliodobenzene, at 298 K, iodobenzene at 329 K.

Finally, Cristau and coworkers have reported on a quite efficient preparation of triphenylphosphine oxide (Figure 2.13) by a similar addition-elimination reaction of red phosphorus with iodobenzene in the presence of a Lewis acid catalyst followed by oxidation of an intermediate tetraarylphosphonium salt.42 This approach holds the potential for the preparation of a variety of triarylphosphine oxides without proceeding through the normally used Grignard reagent. Of course, a variety of approaches is available for the efficient reduction of phosphine oxides and quaternary phosphonium salts to the parent phosphine, including the use of lithium aluminum hydride,43 meth-ylpolysiloxane,44 trichlorosilane,45 and hexachlorodisilane.46... 

Alumina-sodium borohydride, reduction of carbonyl compounds with, 16 572-573 Alumina sols, gelation of, 23 77 Alumina-supported iodobenzene diacetate (IBD), 16 570... 

Palladium-catalyzed reaction of a 3,4-allenol with iodobenzene proceeds through an oxypalladation-reductive elimination sequence to give a 2,3-dihydrofuran efficiently (Scheme 16.8) [13,14],... 

We continued our work with the reductive Heck and Domino-Heck reactions [1, 7J of new bicyclic compound (3) by treating it with different aryl- and hetaryl-iodides, as a result a series of new epibatidine analogues were synthesized, continuously separated and purificated by column chromatography on silica gel. Treatment of 3 with iodobenzene, 2-iodothiophene, 1-iodonapthalene and 2-chloro-5-iodopy-ridine under reductive Heck conditions gave new compounds 4a-d and 5b, 5d as exo-regioisomers after chromatographic separations. The reactions with iodobenzene and 1-iodonapthalene gave only 5-exo- products. The use of trimethylsily-lacetylene under Domino-Heck conditions provided alkynic bicyclic systems 6e andf. 

The phenyl u-anion is strongly basic but may be obtained at relatively modest potentials by reductive cleavage of haloben-zenes when the right cathode material is chosen [63]. Typically, the reactions are carried out at constant current in undivided cells using Cd-coated Ni-cathodes, A1 or Mg sacrificial anodes, DMF (or MeCN for cyanomethylation) as the solvent and BU4NBF4 as the electrolyte. Under these conditions, iodobenzene is reduced at —1.6 V versus SCE and bromobenzene at —1.9 V, which may allow their use in situ [63, 91-93]. 

Buchwald-Hartwig amination of iodobenzene 92 with 2-benzyloxy-4-methyl-aniline 93 affords the diarylamine 94 in high yield (Scheme 32). In this case the Goldberg coupling gives poor yields. Oxidative cyclization of compound 94 using stoichiometric amounts of palladium(II) acetate in acetic acid under reflux leads to the carbazole 95, which by reductive debenzylation provides... 

All the evidence gathered so far points to the conclusion that the RX radicals are intermediates in the reductive cleavage of aryl halides by outer sphere electron donors in polar solvents. This was an already established conclusion for the reduction of several aryl halides in the gas phase (Steelhammer and Wentworth, 1969 Wentworth et al., 1967), and for iodobenzene in apolar or weakly polar matrixes from y-irradiation studies with esr detection at low temperatures (Symons, 1981). It might, however, not have been true in the polar media used in direct and indirect electro-... 

The reductive cleavage of iodobenzene and 3-methyliodobenzene was studied by cyclic voltammetry in both DMF and acetonitrile at 21 and 56 °C at different scan rates and has shown that there is a transition between stepwise and concerted mechanisms at lower scan rates. 1-Iodonaphthalene undergoes a stepwise reductive cleavage with mixed kinetic control by electron transfer and follow-up bond breaking, whatever the scan rate. ... 

Addition of methyllithium to the lactone 1219, followed by reduction with sodium borohydride in refluxing ethanol, afforded, almost quantitatively, ellipticine (228). Reaction of the compound 1219 with the lithio derivative of formaldehyde diethylmercaptal, and reduction with sodium borohydride in refluxing ethanol, led to the mercaptal 1221. Cleavage of the mercaptal 1221 with bis(trifluoroacetoxy) iodobenzene [Phl(OCOCF3)2] in aqueous acetonitrile gave the 11-formyl derivative, which was reduced with sodium cyanoborohydride (NaBHsCN) to 12-hydroxyellipticine (232) (710,711) (Scheme 5.202). The same group also reported the synthesis of further pyiido[4,3-fc]carbazole derivatives by condensation of 2-substituted indoles with 3-acetylpyridine (712). 

Ni(CDC)2" (532) have been reported. Pyrolysis of Co(CDC)3" results in partial reduction of the metal ion to Co(ll) and liberation of iodobenzene and phenyl disulfide. In pyridine solution phenylation of the ligand was observed and yV-cyanodiphenyldithiocarbimate was isolated, (PhS)2C NCN. 

Iodoaniline has been prepared by the reduction of -nitro-iodobenzene 1 by the hydrolysis of -iodoacetanilide formed by the action of iodine monochloride on acetanilide 2 and by the direct iodination of aniline.3 The method described here is an adaptation of the procedure used by Wheeler/ and by Hann and Berliner 5 for the iodination of the toluidines. 

Even when the reductive processes, so evident in metal-stimulated processes, are avoided, several side reactions can still cause reductions in the yield of the desired a-arylated ketones. The first, abstraction of 3-hydrogen atoms from the enolate ion by the aryl radical, has already been mentioned (Section 2.2.2.1) and is sometimes a serious, chain-terminating process.43 5 This abstraction reaction, however, appears to be quite unpredictable. 3-Hydrogen abstraction from the enolate of 2,4-dimethyl-3-pentanone (PriCOPr Table 1) which severely disrupts the reaction with iodobenzene, does not prevent high-yielding reactions of the same enolate (and those from other ketones with a-branching) with many other substrates. In in-... 

The process shown in Eq. (18) is termed reductive elimination, in which the A3-iodanyl group eliminates with concomitant reduction to univalent iodide i.e. iodobenzene and simultaneously with elimination of a heteroatom ligand (BF4) on iodine(III). The same term reductive elimination is widely used in organ -otransition metal chemistry in a somewhat different sense to describe reduction of transition metals with concomitant bond formation between two ligands [Eq. (19)]. 

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