Bromides Experimental Procedure

Di-2-propenyltin dibromide, available from 2-propenyl bromide and tin powder, reacts with aldehydes in the presence of monosodium (+)-diethyl 2,3-dihydroxybutanedioate to give ho-moallylic alcohols in good yields with 42-71% ee the experimental procedure is relatively straightforward98. 

Experimental Procedure 5.2 Suzuki couplinu with a polwvrene-hound arvl bromide [185]... 

Polystyrene-bound allylic or benzylic alcohols react smoothly with hydrogen chloride or hydrogen bromide to yield the corresponding halides. The more stable the intermediate carbocation, the more easily the solvolysis will proceed. Alternatively, thionyl chloride can be used to convert benzyl alcohols into chlorides [7,25,26]. A milder alternative for preparing bromides or iodides, which is also suitable for non-benzylic alcohols, is the treatment of alcohols with phosphines and halogens or the preformed adducts thereof (Table 6.2, Experimental Procedure 6.1 [27-31]). Benzhy-dryl and trityl alcohols bound to cross-linked or non-cross-linked polystyrene are particularly prone to solvolysis, and can be converted into the corresponding chlorides by treatment with acetyl chloride in toluene or similar solvents (Table 6.2 [32-35]). 

Experimental Procedure 6.1 ( omersion of Wang resin into /7-ben/yloxybenzyl bromide resin [49]... 

Cross-linked polystyrene can be directly brominated in carbon tetrachloride using bromine in the presence of Lewis acids (Experimental Procedure 6.2 [55-58]). Thal-lium(III) acetate is a particularly suitable catalyst for this reaction [59]. Harsher bro-mination conditions should be avoided, because these can lead to decomposition of the polymer. Considering that isopropylbenzene is dealkylated when treated with bromine to yield hexabromobenzene [60], the expected products of the extensive bromi-nation of cross-linked polystyrene would be soluble poly(vinyl bromide) and hexabromobenzene. In fact, if the bromination of cross-linked polystyrene is attempted using bromine in acetic acid, the polymer dissolves and apparently depolymerizes [61]. 

Non-activated aryl bromides (but not fluorides) can be used as substrates for palla-dium(0)-catalyzed aromatic nucleophilic substitutions with aliphatic or aromatic amines. These reactions require sodium alcoholates or cesium carbonate as a base, and sterically demanding phosphines as ligands. Moreover, high reaction temperatures are often necessary to achieve complete conversion (Entries 7 and 8, Table 10.4 Experimental Procedure 10.1). Unfortunately, the choice of substituents on the amine... 

Experimental Procedure 10.1 Arylalion ol bcn/ylamine with a support-bound an l bromide [821... 

General Experimental Procedure. A mixture of the amine, 0.1 mole in 250 cc. of absolute alcohol, with 10 g. of sulfuric acid and 28 g. of arseni-ous chloride, cooled to 0°, is diazotized with a saturated aqueous solution of the calculated amount of sodium nitrite (starch-iodide end point). Then, and not before, 1 g. of cuprous bromide is added the mixture is thoroughly stirred, warmed to 60° until no more nitrogen is evolved, and then distilled with steam. The separated arsonic add is recrystallized. 

Bromides and Iodides. The absorption spectra of the gaseous rare-earth halides were measured with a Cary 14 H spectrophotometer. The experimental procedure has been described previously 11). In this study a double furnace was used, allowing the rare-earth halide vapor to be heated to a higher temperature than the solid or liquid and allowing a baseline determination at the temperature of interest. In addition, a 0 0.1 full scale optical density slidewire was employed with the Cary... 

The palladium-catalyzed arylation of diethyl vinylphosphonate using aryl bromides has been reported. The experimental procedure is simple, and the yields are moderate to good (Scheme 5.58). For example, with para-bromobenzaldehyde in MeCN at lOO C, diethyl para-tormyl-trans-styrylphosphonate is formed exclusively in 60% yield. ... 

Kirschning and coworkers have developed several experimental procedures for the stereoselective bro-moacetoxylation or iodoacetoxylation of alkenes based on the interaction of PhI(OAc)2 with iodide or bromide anions [113,114]. The actual reacting electrophilic species in these reactions are the diacetylhalo-gen(I) anions, (AcO)2l and (AcO)2Br , which can also be prepared as the polymer-supported variant [114]. 

A typical experimental procedure is as follows The inclusion complex (ca. 2 g or 1 mmol) or ethyl trans-cinnamate with a-cyclodextrin was exposed to gaseous hydrogen bromide (ca. 2 molar ratio) in a desiccator (ca. 600 ml) in the dark under air at 20 C, After exposure of 20 hr, the excess of the gas was removed by evacuation and the complex was dis-... 

Electrophilic aromatic substitution reactions (Sec. 15.1) are among the best understood of all organic reactions. The qtuilitative aspects of the reactions that are discussed in textbooks include the effect substituents have on the reactivity of arenes toward electrophiles and the orientation, ortho, meta, or para, of their attack on the ring. However, relatively Httle information is given in textbooks about the quantitative differences in rates and reactivities of substituted aromatic compounds. The experimental procedures of this section provide both semiquantitative and quantitative measures of the differences in reactivity of a series of arenes toward the bromo-nium ion, Br, to produce the corresponding aryl bromides (Eq. 15.20). 

The reaction of 1-butylmagnesium bromide (7, Eq. 19.5) with 2-methylpropanal (13) provides an excellent example of the Grignard synthesis of secondary alcohols (Eq. 19.13). In this reaction, the Grignard reagent 7 adds to 2-methylpropanal to give the magnesium salt of 2-methyl-3-heptanol, and the alcohol 14 may be isolated after acidification of the mixture. This transformation is found in Part C of the following experimental procedures. 

In 2000, Nolan and Lee reported the successful application of NHC ligands in this particular arylation reaction [101]. By combining palladium acetate and the imidazolium salt IPr-HCl (IPr = l,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), it was possible to react phenyltrimethoxysUane (as well as vinyltrimethoxysilane) with a variety of aryl bromides and aryl chlorides, including 2-bromopyridine giving the arylated product in high yields (Scheme 1.36) (see Experimental Procedure below). 

Recently, Sarangi et al. (1995) discovered that the Barbier-type allylation of carbonyl compounds could be mediated by zero-valent copper. In the experimental procedure copper(ll) chloride in its hydrated form was mixed with magnesium powder. This reaction did not proceed with anhydrous CuCU, but addition of water to this anhydrous salt in the presence of magnesium allowed the allylation of aldehydes and ketones with allylic bromides. In the absence of halides, the hydrated reagent (CuCl2 2H20/Mg) turned out to be efficient in the reduction of aldehydes. However, the water of crystallization could not suffice and addition of water promoted the reduction process (Sarangi eta/., 1995). 

Typical experimental procedure for the preparation of B-Allyldiisopinocampheylborane 9 and its subsequent allylboration with aldehydes AUyhnagnesium bromide (1.0 mol) is added drop-wise to a stirred solution of B-chlorodiisopinocampheylborane (IPC2BCI, 25) or B-methoxydiisopinocam-pheylborane (IpC2BOMe, 26) (1.05 mol in 1 L ether) at 0 C. After the completion of the reaction as monitored by B NMR (5 79), the reaction mixture is filtered under nitrogen and concentrated under... 

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