Iodobenzene, preparation

Iodobenzene prepared by this procedure may contain traces of nitro compounds. The test for these is to reduce a sample with stannous chloride (or tin) and hydrochloric acid, and treat the resulting acid solution in the cold with a solution of sodium nitrite. If a phenolic odor is obtained on boiling the solution, nitro compounds are still present. A more delicate test can be made by adding the reduced solution, after treatment with sodium nitrite, to an alkaline solution of /3-naphthol an azo dye is formed if nitro compounds were originally present. 

Iodobenzene, as usually prepared, is a very pale yellow liquid of b.p. 188°, and d, 1 83. The freshly distilled pure liquid i colourless, but soon redevelops the yellow colour on exposure to light. Iodobenzene is insoluble in water. 

Meanwhile, during the cooling of the cuprous chloride solution, prepare a solution of benzenediazonium chloride by dissolving 20 ml. (20-5 g.) of aniline in a mixture of 50 ml. of concentrated hydrochloric acid and 50 ml. of water, and after cooling to 5°, adding slowly a solution of 17 g. of sodium nitrite in 40 ml. of water. Observe carefully the general conditions for diazotisation given in the preparation of iodobenzene (p. 184). 

Many examples of insertions of internal alkynes are known. Internal alkynes react with aryl halides in the presence of formate to afford the trisubstituted alkenes[271,272]. In the reaction of the terminal alkyne 388 with two molecules of iodobenzene. the first step is the formation of the phenylacetylene 389. Then the internal alkyne bond, thus produced, inserts into the phenyl-Pd bond to give 390. Finally, hydrogenolysis with formic acid yields the trisubstituted alkene 391(273,274], This sequence of reactions is a good preparative method for trisubstituted alkenes from terminal alkynes. 

The carbonyiation of o-diiodobenzene with a primary amine affords the phthalimide 501 [355,356]. Carbonyiation of iodobenzene in the presence of (9-diaminobenzene (502) and DBU or 2,6-lutidine affords 2-phenylbenzimida-zole (503)[357, The carbonyiation of aryl iodides in the presence of pentaflnor-oaniline affords 2-arylbenzoxazoles directly, 2-Arylbenzoxazole is prepared indirectly by the carbonyiation of (9-aminophenol[358j. The optically active aryl or alkenyl oxazolinc 505 is prepared by the carbonyiation of the aryl or enol triflates in the presence of the opticaly active amino alcohol 504, followed by treatment with thionyl chloride[359]. 

The Li compound 588 formed by the ort/io-lithiation of A. A -dimethylaniline reacts with vinyl bromide to give the styrene derivative 589(433]. The 2-phe-nylindole 591 is formed by the coupling of l-methyl-2-indolylmagnesium formed in situ from the indolyllithium 590 and MgBr2, with iodobenzene using dppb[434]. 2-Furyl- and 2-thienyllithium in the presence of MgBr2 react with alkenyl halides[435]. The arylallenes 592 and 1,2,4-alkatrienes are prepared by the coupling reaction of the allenyllithium with aryl or alkenyl halides[436]. 

Pentamethylcyclopentadienyl substituted boron complexes arc obtamed by the reaction of the pentamethylcyclopentadienyl anion with boron tnfluonde [109] (Table 27) Similarly, the Gngnard reagent prepared from 3,5-bis(tnfluorometh-yl)iodobenzene reacts with sodium tetrafluoroborate to form the phase-transfer eatalyst 2 under anhydrous eonditions [110] (equation 87)... 

Similar methodology has been used to prepare the dialkoxyphosphinyldi-fluoromethylcopper compound 242 (equation 160) Functionalization with allyl bromide, methyl iodide, and iodobenzene occurs readily, as well as stereospecific syn addibon to hexafluoro-2-butyne [243. ... 

Willgerodt4 prepared iodosobenzene diacetate by adding chlorine to iodobenzene and hydrolyzing the dichloride to iodosobenzene, which was then reacted with acetic acid. Pausacker 6 used this method to synthesize a number of analogs but found it... 

Iodosobenzene diacetate is best prepared by the action of peracetic acid and acetic acid on iodobenzene. The present procedure is superior to earlier ones 5-8 because it uses inexpensive, commercially available peracetic acid, is faster, and gives higher yields. The procedure seems general for aiyl iodides with electron-releasing substituents, for the submitters have obtained good yields of diacetates from o-, m- and />-iodoto uene, 2- and 4-iodo-wt-xyiene, 2-iodo-/>-xylene, o-iodophenetole, and 4-iodobi-phenyl. 

Iodoxybenzene has been prepared by the disproportionation of iodosobenzene,4Hi by oxidation of iodosobenzene with hypo-chlorous add or bleaching powder,7 and by oxidation of iodobenzene with hypochlorous acid or with sodium hydroxide and bromine.8 Other oxidizing agents used with iodobenzene include air,3 chlorine in pyridine,9 Caro s acid,19-11 concentrated chloric acid,15 and peracetic acid solution.13 Hypochlorite oxidation of iodobenzene dichloride has also been employed.14... 

One of the best methods for the introduction of iodine into aromatic rings is the reaction of diazonium salts with iodide ions. Analogous reactions with chloride, bromide, and fluoride ions give poorer results, and 14-25 and 13-20 are preferred for the preparation of aryl chlorides, bromides, and fluorides. However, when other diazonium reactions are carried out in the presence of these ions, halides are usually side products. Aniline has also been converted to fluorobenzene by treatment with t-BuONO and Sip4 followed by heating. A related reaction between PhN=N—N C4Hg and iodine gave iodobenzene. ... 

The de Meijere group [63] prepared interesting spiro-compounds containing a cyclopropyl moiety using a combination of a Heck and a Diels-Alder reaction, with bicyclopropylidene 6/1-115 as the starting material. The transformation can be performed as a three-component process. Thus, reaction of 6/1-115, iodobenzene and acrylate gave 6/1-116 in excellent yield. With vinyliodide, the tricyclic compound 6/1-117 was obtained (Scheme 6/1.31). Several other examples were also described. 

Quinoxalines 85 have been prepared by the reaction of diols with benzene-1,2-diamines in the presence of a ruthenium catalyst <06TL5633>. Iodobenzene diacetate has been suggested as a less toxic alternative to lead tetraacetate for the oxidative cyclisation of iminooximes to quinoxaline iV-oxides 86 <06TL4969>. 

The second most popular method of oxadiazole preparation starts from acylhydrazones 110, which undergo cyclization usually under the action of oxidizing agents (Br2, PhN02, HgO, iodobenzene diacetate). Also, the use of acetic anhydride can lead to cyclization of compound 110. The cyclization can be supported by microwave irradiation. In particular cases, heating is sufficient to accomplish the reaction. 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

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... 

Free or benzo-fused 1,2,3-triazoles 286 have been prepared by iodobenzene diacetate-mediated oxidation of hydrazones 285 (Equation 37) <2000SC417>. 

A noteworthy novel preparative technique has been developed for the synthesis of [Pt(S-Me2SO)2Cl2] from the reactive intermediate [Pt(IPh2)2Cl4] the by-products here are ultimately chlorobenzene and iodobenzene (334). Some problems were initially observed in the synthesis of [M(S-Me2SO)2Cl2] (M = Pd, Pt) by conventional means, as the original syntheses (127) were found to be somewhat irreproducible (357). 

Additional examples of palladium-catalyzed cross-couplings, in particular with allenylzinc compounds, can be found elsewhere [11, 15, 36]. A systematic study comparing several chiral palladium phosphine catalysts in the reaction of 4,4-di-methyl-1,2-pentadienylzinc chloride and iodobenzene revealed that an enantiomeric excess of only 25% was obtained from the best catalyst combination PdCl2 and (R,R)-DIOP [15]. The synthetic value of these transformations of donor-substituted allenes as precursors is documented by the preparation of a/l-unsaturatcd carbonyl... 

Fused isooxazolidines can be prepared efficiently in a one-pot procedure, which involves a sequence of a Pd-catalyzed reaction of iodobenzene with allene, nucleophilic substitution and nitrone 1,3-dipolar cycioaddition (1,3-DC) (Scheme 16.14) [18]-... 

Iodoxybenzene.—The major portion of the iodosobenzene so prepared is made into a paste with a little water and submitted to steam distillation in a round-bottomed flask. The distillation is continued until all the material has dissolved and the iodobenzene produced has passed over (use a condenser and receiver). The residue after the distillation (if still turbid) is filtered while hot and the filtrate is concentrated on the water bath until a sample, poured... 

S-Alkynyl phosphorodithionates have been prepared in high yield by the nucleophilic displacement of iodobenzene from alkynyl phenyl iodonium salts [65]. 

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