Dibromomethyl ketones

Aroylformamido-4-aryl-l,2,5-thiadiazoles 156 can also be prepared from aryl dibromomethyl ketones 155 on treatment with tetrasulfur tetranitride at 115 °C (Equation 31) <1995J(P1)253>. These reactions are, however, complex, and the 1,2,4-thiadiazole 157 is often produced as a minor product. 

Homologation of ECHO to a-bromo-a, -enones.4 The initial steps of this homologation involve addition of dibromomethyllithium (1) to an aldehyde followed by oxidation of the adduct to a dibromomethyl ketone (2). The aluminum enolate of 2 undergoes an aldol reaction to provide an a-bromo-p-hydroxy ketone... 

Interaction of hydrogen iodide and diazoketones forms methyl ketones with the liberation of nitrogen and iodine (method 228). If the diazoketone is treated with bromine, then a dibromomethyl ketone, RCOCHBtj, is formed, ... 

Stereospecific Favorskii rearrangement czs-a,/ -EthyIenecarboxylic acid esters from dibromomethyl ketones... 

Dibromomethyl ketones from acetylene derivatives G = CH -> GOGHBrg... 

Aldehydes, Ketones, ndAcids. As with many aromatic compouads, the oxidatioa of methyl groups is an attractive synthetic route to both aldehydes and carboxyUc acids ia the quiaoliaes. The hydrolysis of dibromomethyl groups has also beea used for aldehydes and the hydrolysis of nitriles for carboxyhc acids. Detailed reviews of the synthesis of these compounds have appeared (4). 

Bromomethyl ketones.l Reaction of (dibromomethyl)lithium (1) with esters and then with BuLi (excess) generates the enolate (a) of a bromomethyl ketone. Quenching with acidic ethanol gives the bromomethyl ketone (2) in 70-85% yield. Quenching with A O generates bromo enol acetates. 

A methodically related transformation, the copper(Il)-mediated transfer of a cyano(ethoxycar-bonyl)methylene unit from ethyl cyanoacetate to alkenes, is presented in Section I.2.I.2.4.2.9. The copper-mediated synthesis of cyclopropyl ketones from a,a-dibromo ketones and alkenes seems to be of very limited scope and even less efficient than the corresponding synthesis of cyclopropanecarboxylic acids from o ,a-dibromoacetates (vide supra). The reaction (toluene, 100°C, 93 h) of cyclooctene (4.0 mmol), dibromomethyl phenyl ketone (8.0mmol), and commercial grade copper powder (18 mmol) activated with iodine (0.2 mmol) gave exy-9-benzoyl-bicyclo[6.1.0]nonane (7, 12%) and (2-oxo-2-phenylethyl)cyclooct-l-ene (8, 3%). ° A similar treatment of styrene gave l-benzoyl-2-phenylcyclopropane in only 2% yield [ratio (cisjtrans) 1 l.b]. " ... 

A test tube fitted with a three-way stopcock was filled with argon by repeated evacuation and back-filling. To a benzene solution (3 mL) of dibromomethyl phenyl ketone (0.278 g, 1.0 mmol) was added pentacar-bonyliron [Fe(CO)j, 0.234 g, 1.2 mmol], and the solution was heated at 80 C with stirring. The precipitate was separated by filtration through a thin layer of alumina. The concentrated solution was poured into petroleum ether, thus giving rran5-l,2,3-tribenzoylcyclopropane as a colorless product yield 28%. This procedure is representative for those carried out with octacarbonyldicobalt or bis(cycloocta-l, 5-diene)nickel rather than pentacarbonyliron. 

With the presence of more than one halogen atom in the a-position of the halo ketone, the formation of 2-oxoalkylphosphonates becomes more difficult, and the reactions proceed exclusively according to the Perkow reaction. Thus, dichloromethyl, dibromomethyl, and tribromomethyl methyl ketones, in reaction with trialkyl phosphites, lead to the corresponding vinyl phosphates... 

A useful one-carbon ring-expansion reaction which has been developed involves treatment of l-(dibromomethyl)-cycloalkan-l-ols with n-butyl-lithium in hexane to give the ring-expanded ketones, usually in excellent yield e.g. l-(dibromomethyl)-cyclododecan-l-ol, which was obtained by treating cyclododecanone with dibromo-methyl-lithium, gave cyclotridecanone in 89% isolated yield. ... 

Dibromoalcohols, which are readily prepared by addition of dibromomethyl-lithium to aldehydes or ketones, undergo reductive elimination on treatment with zinc and acetic acid in refluxing methylene chloride to give vinyl bromides as mixtures of E- and Z-isomers (Scheme 30). Conjugated 1-bromo-dienes or -trienes can be prepared from the appropriate unsaturated carbonyl compounds. 

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