Thallium hydroxide

In the total synthesis of the naturally occurring big molecule of palytoxin, which has numerous labile functional groups, this coupling is the most useful for the creation of E, Z-conjugated diene part 653. In this case, thallium hydroxide as a base accelerates the reaction 1000 times more than KOH[523]. Even TECOj can be used instead of a strong base in other cases[524]. 

Porphyrin, octaethyl-, thallium hydroxide complex cyclic voltammetry, 4, 399 <73JA5140)... 

When this coupling is extended to more complex substrates, the rate slows drastically and undesired by-products are formed, even when 1 equiv. of Pd(0) is used.5 Fortunately the rate is markedly affected by the choice of the base, being highest with thallium hydroxide. Under TlOH conditions the coupling to (E,Z)-and to (Z,Z)-dienes can be effected at 0° often within minutes. Under these improved conditions (Z)-l and (Z)-2 couple to form (Z,Z)-3 in 73% yield, and (E)-1 and (Z)-2 couple to give (E,Z)-3 in 94% yield. 

Thallium compounds, 24 629-635 properties of, 24 631t Thallium dichromate, 6 538 Thallium halides, uses for, 24 636 Thallium hydrides, 24 632 Thallium hydroxides, 24 632-633 Thallium intoxication, 24 638, 639... 

Thallium has much the same look (silvery) and feel as lead and is just as malleable. Unlike lead, which does not oxidize readily, thallium will oxidize in a short time, first appearing as a dull gray, then turning brown, and in just a few years or less turning into blackish corroded chunks of thallium hydroxide. This oxide coating does not protect the surface of thallium because it merely flakes off exposing the next layer to oxidation. 

Thallium oxide also can he prepared hy thermal dissociation of thallium hydroxide, TlOH or thallium carbonate, TI2CO3. Thallium oxide dissolves in water forming thallous hydroxide, TlOH. It reacts with carbon dioxide to form thallous carbonate, TI2CO3. 

Many cyclopentadienylthallium(I) compounds have been described in the literature the first one, cyclopentadienyl thallium (Lilia), was synthesized by Fischer and Hofmann (160) nearly 30 years ago. The colorless solid can be best prepared from cyclopentadiene and thallium hydroxide or thallium(I) salts in the presence of alkali in aqueous solution (171) [Eq. (11)]. The ring-substituted species LUIb-i (172,173,268,270) (Table V) as well as hydro-... 

Silver salts are also common activators in numerous Suzuki coupling reactions. The earliest example could probably be found in the Kishi s palytoxin synthesis. Silver oxide as well as thallium hydroxide provided dramatic rate enhancements in the couplings of vinylboronic acids (Scheme 10.41).69 Both thallium and silver ions are most probably abstracting halide in palladium intermediates, but silver is clearly the most efficient. Moreover, with the right counterion, the silver salt also acts as a mild base and activator. 

Roush, Nicolaou, and Evans have also demonstrated the efficiency of thallium hydroxide in tlie synthesis of an aglycone of the antibiotic kijanimicin [84], chlorothricolide [85], (5Z, 8Z, lOE", 12R, 14Z)-12-hydroxy-5,8,10,14-icosatetraenoic acid [(IZR)-HETE] [86], and a macrolide antibiotic, rutamycin B [87] (Scheme 2-30). 

The selectivity (C-2 C-4 2,4-disubstitution) of Suzuki couplings of 2,4-dibromopyridine varies greatly with catalyst and conditions. The most selective C-2 mono-coupling is obtained using Pd(PPh3)4 with thallium hydroxide as base. (Caution Thallium hydroxide is very toxic.)... 

Orthothombic crystals. Very sensitive to moisture- df 8.36. d 8,65 also reported Hebecker, Hoppe, JVafurtviss. 53, 104 (1966). mp 550". Dec on heating in air, but may be melted in an atm of fluorine. Instantly dec by water, forming thallium hydroxide and a dark brown sediment. May be stored in sealed quartz tubes. 

Tl reacts with water to form thallium hydroxide and hydrogen gas. 

In 1952, Pfeil and Schroth reported that, in formose formation, the Cannizzaro reaction takes part, simultaneously and competitively, with the addition reaction. Whereas alcohols of low molecular weight, 1,4-dioxane, tetrahydrofuran, and other compounds repress the Cannizzaro reaction, the hydroxides of alkaline-earth and alkali metals activate the reaction, with only one exception, namely, thallium hydroxide, which catalyzes the addition reaction specifically. In 1971, the two reactions, namely, the addition reaction and the Cannizzaro reaction, were quantitatively and differentially measured by Fujino. When measured for the... 

Method L is conducted with thallium hydroxide as the base and Pd(PPh3)4 as catalyst under very mild reaction conditions to afford a wide variety of biaryls, including highly encumbered, in fair yields [16]. The biaryl 189 was prepared from mesitylboronic acid (283) and iodobenzene in almost quantitative yield. Scheme 23. Whereas tri-ort/io-substituted biphenyls were obtained by this method in respective yields, synthesis of tetra-ort/io-substituted analogues failed [16], Among base-sensitive groups, only an ester function has survived thallium hydroxide-mediated reactions at room temperature. Concerning the extreme toxicity of thallium compounds, the method is applicable only in the small-scale labo-synthesis. 

Thallium hydroxide-mediated room temperature SM reactions with sterically hindered substrates Preparation of 2,4,6-trimethyl-2 -nitrobiphenyl (358) fib ... 

Thallium cyclopentadienide is, however, more conveniently prepared by the reaction of thallium hydroxide with cyclopentadiene, a procedure which will be described under Method 2. 

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