Iodine halides, diphenyl

Attempts to directly iodinate quinoxaline failed, and the synthesis of 2,3-diphenyl-5,8-dibromoquinoxaline is somewhat more involved (Scheme 9) [61]. Starting from ort/zo-phenylenediamine, reaction with SOCI2 gives benzothia-diazole in high yield. Bromination in HBr furnishes 4,7-dibromobenzothiadi-azole, which can be alkynylated or directly reduced [62]. Reduction of the dibromide with sodium borohydride leaves the halide substituents unmolested but opens the ring to furnish l,4-dibromo-2,3-diaminobenzene. Reaction of this intermediate with a 1,2-dione furnishes a 2,3-disubstituted 5,8-dibromo-quinoxaline. Pd-catalyzed alkynylation finishes the sequence off and removal of the TMS groups yields the desired 5,8-diethynylquinoxaline monomers (Table 9, entries 13,14). 

Oxo-1-propen-1-yl tellurium iodides did not react with iodine. The attempt to prepare mixed (chloride, bromide) tellurium trihalides was unsuccessful a mixture of trichlorides and tribromides was formed. When 1,3-diphenyl-3-oxo-l -propen-l-yl tellurium iodide was reacted with bromine, the bromide and elemental iodine were the only observed products. The 3-oxo-l-propen-l-yl tellurium trihalides are thermally unstable they decompose on mild heating to the tellurium halide and elemental halogen1. 

Apart from their behaviour as ligands in metal catalyst systems, studies of the reactivity of phosphites towards a wide variety of other substrates have attracted attention. New aspects and applications of the classical Michaelis-Arbuzov reaction and its variants continue to appear. Evidence of the thermal disproportionation of methyltriaryloxyphosphonium halides formed in the reactions of triarylphosphites with alkyl halides, together with the formation of P-O-P intermediates, has been reported. The Michaelis-Arbuzov reaction has been used in the synthesis of phosphonate-based styrene-divinylbenzene resins and polyphosphonated chelation therapy ligands.Treatment of electron-rich benzylic alcohols dissolved in triethylphosphite with one equivalent of iodine affords a low-temperature one-pot route to the related benzylic phosphonates, compounds which are otherwise difficult to prepare. Upper-rim chloromethylated thiacalix[4]arenes have also been shown to undergo phosphonation on treatment with a phosphite ester in chloroform at room temperature. The nickel(II)-catalysed reaction of aryl halides with phosphite esters in high boiling solvents, e.g., diphenyl ether, (the Tavs reaction), has also... 

Thallium diphenyl bromide was first mentioned by Meyer and Bertheim in 1994, but in 1922 the present authors showed that this compound was impure, and that the reactions given for it did not represent the facts, as shown by them later preparation. They therefore claimed their preparation to be the first organometallic compound of thallium, in the aromatic series, to be obtained in the pure state. The compound, which is typical of the aromatic thallium diaryl halides, does not melt below 300 C., and may be crystallised from pyridine. The corresjjond-ing chloride is decomposed "by iodine monochloride according to the equation ... 

The living cationic polymerizations discussed above are invariably based on the nucleophilic iodide counteranion (activation of the carbon-iodine terminal bond Eq. 3). It is expected, however, that similar living processes are equally possible with other counteranions that can exert, as the iodide anion does, a suitably strong nucleophilic interaction with the growing carbocation. We have in fact found the phosphate anions to meet this requirement (10). Similarly to hydrogen iodide, monoacidic phosphate esters [H0P(0)R 2 R alkyl, alkoxyl, etc.] like diphenyl phosphate ( ) form a stable adduct 5) with a vinyl ether (Eq. 5). Zinc chloride or iodide then activates the phosphate bond in 5 by increasing its polarization (as in 6), and living cationic polymerization proceeds via an intermediate (7) where the carbocationic site is stabilized by a phosphate anion coupled with the zinc halide activator. 

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