Bromo-2-methylnaphthalene

A small amount of iodine and iron powder is added to a solution of 142 g. (1.0 mole) of 2-methylnaphthalene in 300 ml. of carbon tetrachloride. The mixture is cooled to 0°, and a solution of 160 g. (1.0 mole) of bromine in 300 ml. of carbon tetrachloride is added (8 hours) with stirring and exclusion of light, during which time the temperature is not allowed to rise above 5°. (Hood.) After standing overnight, the solution is washed with 10% sodium hydroxide solution and water followed by drying over calcium chloride. Distillation gives 186 g. (84%) of l-bromo-2-methylnaphthalene, b.p. 152-156°/14 mm. 

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A mixture of 210 g. (0.95 mole) of l-bromo-2-methylnaphthalene (p. 51), 160 g. (0.90 mole) of N-bromosuccinimide (p. 59), 1 g. of benzoyl peroxide, and 250 ml. of carbon tetrachloride is refluxed for 2.5 hours. Carbon tetrachloride (250 ml.) is added, and the warm mixture is filtered. The solid residue is washed several times with fresh carbon tetrachloride. The combined filtrate is concentrated and cooled, and the precipitated product is filtered off. There is obtained 230 g. (85%) of l-bromo-2-bromomethylnaphthalene melting at 103.5-105.5°. 

The alkyl halide may be replaced by an alkyl sulfate. For example, 1,2-di-methylnaphthalene is formed in 76% yield when 1 -bromo-2-methylnaphthalene is treated with lithium in ether and the product of this reaction is treated with dimethyl sulfate.319... 

Pig. 2. Time-resolved emission of bromonaphthalenes in hexane at room temperature resulting from excitation by a 266-nm, 10-ps pulse. The emission i within the range of 310-550 nm. Plots of emission intensity vs. time (ps) for (a) 1-bromonaphthaiene, (b) l-bromo-2-methylnaphthalene, (c) l-bromo-4-methylnapthaiene, and (d) 2-bromonaphthaleoe. 

The Grignard reagent 628 was prepared by adding a solution of l-bromo-2-methylnaphthalene (629) in dry diethyl ether to magnesium ribbons under ultrasonic irradiation and was diluted with toluene (toluene / diethyl ether, 1 1) to produce a yellow slurry whose concentration was 0.3-0.4 M [34]. 

In this study, the full catalytic cycle for the recently reported asymmetric Suzuki-Miyaura coupling between 1 -bromo-2-methylnaphthalene (2) and 1 -naphthal eneboronic acid (3) catalyzed by a [Pd(bis-hydrazone)] (1) complex [47], was theoretically investigated by means of DFT calculations. Importantly, the results derived from this study revealed that the transmetalation reaction does not occur in just one step, but occurs in three steps. This is owing to the relative lability of the bis-hydrazone ligand, which can easily dissociate one of the N atoms coordinated to the Pd catalyst. Very recently, this variant for the transmetalation mechanism has been reported for the Suzuki-Miyaura coupling catalyzed by a diimine chelated palladium complex [15]. 

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