Aliphatic Bromides

2 Aliphatic Bromides. The remarks under aliphatic chlorides apply quite generally to the corresponding bromides. 

6 Aromatic Halides. The molecular ion peak of an aryl halide is readily apparent. The M — X peak is large for all compounds in which X is attached directly to the ring. 

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A simple procedure is developed for conversion of aliphatic bromides into methyl 1-alkyl-1,2,3-triazole-4-carbox-ylates 1083. In the first step, alkyl bromide reacts with polymer-supported azide 1081 to provide a solution of azide... 

In a similar type of reaction, polymer-supported hydridoiron tetracarbonyl anion reacts with simple non-benzylic aliphatic bromides and iodides to produce aldehydes (Table 8.15), presumably through the intermediate formation of RCOFeH(CO)3, which undergoes reductive extrusion of the aldehydes [3], In contrast, benzylic halides and a-halocarbonyl compounds are reductively dehalogenated by the HFe(CO)4 anion (see Chapter 11). 

More data were gathered later concerning the reaction of iron(i) and also iron(o) porphyrins with various aliphatic bromides (Lexa et al., 1988). In the case of iron(o) porphyrins, the a-alkyl-iron(ii) complex is obtained directly... 

Stereoselective alkylation with aliphatic bromides and iodides of the Schiff bases of tert-butyl glycinate with (—)-(15,25,55)-2-hydroxypinan-3-one or (+)-(lR,2R,5R)-2-hydroxy-pinan-3-one 150 was reported to produce lipidated amino acids as d- and L-enantiomers in 80 to over 90% ee. 151 Similarly, the asymmetric synthesis of a derivative of arachidonic acid (4) has also been reported. The pure enantiomer was obtained via regioselective functionalization of a chirally pure glutamic acid. 152 ... 

A general method of introducing the acid fluoride functionality in aryl bromides 12 is their carbonylation under an atmospheric pressure of carbon monoxide in dimethylformamide in the presence of potassium fluoride.33 Several catalytic systems, solvent and the effects of temperature, amount of potassium fluoride used and pressure of carbon monoxide were systematically investigated to find the right conditions to obtain the aroyl fluorides 13. The carbonylation of unactivated aliphatic bromides was unsuccessful. 

What procedures arc available for preparing an aliphatic bromide ... 

Silver salts of carboxylic acids react with bromine or chlorine in an inert solvent to give carbon dioxide, a silver halide, and the halide containing one less carbon atom than the acid. The method has been reviewed. " Both low- and high-molecular-weight aliphatic bromides have been prepared. "t i i The degradation of silver salts of aromatic acids is complicated by nuclear halogenation." The procedure is valuable as a step in the synthesis of oi-bromo esters (C, to C,) from dicarboxylic acids. ... 

The aromatic bromides which contain bromine in the benzene nucleus are either colourless liquids or crystals, which in contrast with the side-chain substituted isomers in part possess an aromatic odour, and their vapours do not attack the eyes and nostrils. The bromine is held very firmly in them, more firmly than in the aliphatic bromides, and cannot he detected by stiver nitrate. While the aliphatic bromides, as mentioned under bromethyl, decompose with ammonia, alcohol, alkalies, etc., to form amines, ethers, alcohols, etc., respectively, these reagents do not act on the aromatic bromides. The bromides containing the bromine in the side-chain, behave like their aliphatic analogues. 

Thallous carboxylates have also been utilized by Taylor and McKillop6 in the Hunsdiecker reaction yields of primary aliphatic bromides are extremely high, fle-... 

Photocatalysis of radical cyclization. This system, when irradiated, can effect dchalogcnation of aliphatic bromides and aryl halides via a radical intermediate.1 It can also effect radical cyclization of l-allyloxy-2-halobenzenes (equation I) in 76% isolated yield.2... 

The reaction is of broad scope being applicable to primary aliphatic bromides, benzylic bromides and aryl bromides although in the latter cases, an additional palladium catalyst [PdfPPh J ] is required. With reaction temperatures of 150°C and CO pressures of 80-100 p.s.i., yields are generally in excess of 80%. The success of this method with primary aliphatic bromides is also noteworthy as such systems often undergo 8-eliminations rather than carbonylation a new platinum catalyst has been developed which also does not suffer appreciably from this limitation.1 5... 

C-Br Stretch (strong) in aliphatic bromides occurs at 650-510 cm, out of the range of routine spectroscopy using NaCl plates or cells. The trends indicated for aliphatic chlorides hold for bromides. Aryl bromides absorb between 1075 and 1030 cm . ... 

Aliphatic bromides > aliphatic chlorides = aromatic bromides > aromatic chlorides... 

It is also known that aromatic bromides have a higher decomposition temperature (250°C-300°C) than aliphatic bromides (200°C-250°C). 

Danen, W. C., and R. J. Warner The Remarkable Nucleophlicity of Superoxide Anion Radical. Rate Constants for Reaction of Superoxide Ion with Aliphatic Bromides. Tetrahedron Letts 1977, 989. 

Organometallic Reagents - Thallium (I) carboxylates, which are easily prepared and purified and are stable indefinitely, undergo the Hunsdiecker reaction in approximately three times the yield afforded by silver salts. Thallium salts are al3o useful in alkylation of purines, and in synthesis of aryl iodides and bromides as well as aliphatic bromides. ... 

In 2011 Tomioka and co-workers expanded their previously reported Cu-catalysed asymmetric allylic arylation of aiyl Grignard reagent and cinnamyl bromides [33] to the corresponding aliphatic bromides [34]. For this purpose, structural steric and electronic modifications of their chiral Cu(I)-NHC Cl catalyst... 

Stoichiometric amounts of tetraethylammonium cyanide react with aliphatic bromides in dichloromethane, acetonitrile or DMSO to give reasonable yields of the corresponding nitriles [13]. These reactions are clearly related to, but not actually examples of, phase transfer catalysis. It is interesting, however, that under these homogeneous conditions, tetraethylammonium cyanide reacts in acetonitrile with neopentyl bromide to give the corresponding nitrile (see Eq. 7.3). Bimolecular displacements on such sterically hindered substrates are usually quite difficult to effect. 

Reductions with NaBH4/D20 and NaBD4/D20 show that the hydrogen atom is derived from NaBH4. By simply using the NaBH4-ACVA system, aliphatic bromides are not reduced and the reaction rate of aryl bromides is lowered. 

Aliphatic bromides from other halides and sulfonates. 347... 

The unreactivity of l-bromoadamantane with 02 demonstrated a lack of any appreciable electron transfer type substitution process (eq. 12). Although an electron transfer type mechanism has been demonstrated for nitroaromatic halides (see Section II. C), the difference in reduction potentials between O2 and aliphatic bromides is apparently too great to allow such a transfer to occur. 

Xia et al. [39] have found that out of these three catalysts only the Cu-CPSIL is effective for the reaction of aliphatic bromides with sodium azide and alkyne to produce 1,2 -triazoles under the optimized condition as the copper on CPSIL showed high dispersion and the interaction between the copper and support is different in case of Cu-CPSlL than the other two as evidenced by the X-ray photoelectronic spectroscopic (XPS) analysis. Based on experimental evidences and literature reports [40,41]/ they provide a possible pathway for this transformation as depicted in Scheme 23. 

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