Raymond Price

Reactions of coordinated ligands: IX. chromium(0)-promoted intramolecularnucleophilic substitution of an aryl halide: a preparation of chroman☆

Abstract When treated with potassium t-butoxide in dimethyl sulphoxide the chromium tricarbonyl complex of 3-(2-fluorophenyl)propan-1-ol underwent a rapid intramolecular nucleophilic substitution to give the corresponding complex of chroman, from which the heterocycle was obtained by oxidation with iodine. With metal alkoxides the chromium tricarbonyl complex of 2-(2-fluorophenyl)ethanol gave either mixtures (from which the product of intramolecular nucleophilic substitution was not isolated) or the products of intermolecular nucleophilic substitution.

Reactions of co-ordinated ligands. Part 10. Rhodium-catalysed cyclisation of 3-(2-fluorophenyl)propanols to chromans

The cyclisation of several 3-(2-fluorophenyl)-propanols to the corresponding chroman occurs in nitromethane–acetone solution at 80 °C when either the hexafluorophosphate (3) or tetrafluoroborate salt (4) of the (η5-ethyltetramethylcyclopentadienyl)(η6-benzene)rhodium(III) cation is used as a catalyst; the former salt is the more effective catalyst. The cyclisation is believed to involve the activation of the aryl fluoride (towards intramolecular nucleophilic substitution by the hydrpxy group) by the formation of a metal complex in which the aryl fluoride is π-bonded with the metal cation. It is suggested that the arene-exchange reaction which gives this π-bonded complex proceeds faster with the salt (3) than with the salt (4), and that this is the main factor for the greater efficiency of the former salt as a cyclisation catalyst.

Intramolecular nucleophilic substitutions of co-ordinated aryl halides. A preparation of chromans

3-(o-Fluorophenyl)propan-1-ol can be cyclised readily to chroman either through chromium tricarbonyl complexes or (as also with substituted fluorophenylpropanols) by the action of the (η6-benzene)(η5-ethyltetramethylcyclopentadienyl)rhodium(III) cation.

Phosphonation of aryl halides by copper(I) complexes of trialkyl phosphites

The copper complexes [Cu3(O2CMe)5{P(OR)3}2](1; R = Me or Et), [Cu(O2CMe){P(OR)3}(bpy)](2; R = Me or Et)(bpy is 2,2′-bipyridine), and [Cu(O2CMe){P(OEt)3}2] react with certain 2-halogenoazobenzene compounds, ArX, at room temperature to form the corresponding dialkyl arylphosphonates, ArP(O)(OR)2, and the products, ArH and Ar2, of reductive substitution and biaryl coupling. The ester, MeCO2R, and a copper(I) halide complex (e.g. [CuX{P(OR)3}]) are also formed. Kinetic studies of the reactions of some of these copper complexes with 2′-acetamido-6-bromo-4′-diethylamino-2,4-dinitroazobenzene in alcohol solution show that the phosphonation reactions are equal concentration second-order processes in each case. The effects of a radical scavenger and of light on the reaction suggest the involvement of radicals in the formation of ArH and Ar2, but not in the formation of ArP(O)(OR)2. The effects of different substituents in ArX, of changes in solvent, and of various additives on these reactions are investigated. A mechanism involving concerted nucleophilic substitution within the coordination sphere of copper(I) is proposed.

The copper-promoted reaction of o-halogenodiarylazo-compounds with nucleophiles. Part 1. The copper-promoted reaction of o-bromodiarylazo-compounds with trialkyl phosphites. A novel method for the preparation of dialkyl arylphosphonates

o-Bromodiarylazo-compounds react with triethyl phosphite in the presence of copper(II) acetate in dry ethanol to give the corresponding o-diethylphosphonatodiarylazo-compounds in good yield. Reaction is facilitated by the presence of an o′-donor substituent in the o-bromodiarylazo-compound. In 10% aqueous ethanol reductive replacement competes with nucleophilic substitution in o-bromodiarylazo-compounds having an o′-donor suestituent but not in those devoid of such a substituent. Under these conditions reduction of the copper(II) acetate to a copper(I) species occurs with liberation of acetic acid. The former o-bromodiarylazo-compounds readily undergo reductive substitution in the presence of acetic acid or, better, trifluoroacetic acid and copper(I) acetate or copper–bronze in ethanol, whereas the latter do not. In the presence of acetic acid biaryl coupling competes with reductive substitution and becomes the principal reaction when no acid is present. Neither reductive substitution nor biaryl coupling occur when the copper(I) acetate or copper–bronze are replaced by copper(II) acetate.

Influence of substrate structure on copper(I)-assisted cyanide substitution in aryl halides

The synthesis of various aryl halides is described: these are designed to explore the structural characteristics which are sufficient to enable copper(I)-assisted substitution of the halide by cyanide to proceed. The copper ion serves to polarise the substrate; stable co-ordination complexes are not formed. The role of various heteroatoms in the substrate is assessed and the importance of intramolecular hydrogen bonding is established.

Cyanide substitution in aryl halides by copper(I) complexes derived from formamide and from formaldehyde oxime

The copper complexes [Cu3(CN)4L4][L = MeCN, pyridine (pyr)], [Cu(CN)(pyr)2] and [Cu2(O2CMe)(CN)] derived from formamide, and [Cu3(O2CMe)5(MeCONH2)(CH2NOH)2] and [Cu(O2CMe)(CH2NOH)2] derived from formaldehyde oxime (formaldoxime) react with 2′-acetamido-6-bromo-4′-diethylamino-2,4-dinitroazobenzene, ArBr, to form the corresponding aryl cyanide, ArCN, and the products ArH and Ar2 of reductive substitution and biaryl coupling. Copper(I) bromide complexes are also formed. Kinetic studies of these reactions in acetonitrile solution show that the cyanation reactions are equal concentration, second-order processes in each case. The effect of a radical scavenger on the reaction suggests the involvement of radicals in the formation of Ar2, but not in the formation of ArCN. A mechanism involving concerted nucleophilic substitution within the co-ordination sphere of copper(I) is proposed.

Formaldehyde oxime as a precursor to cyanide in mixed-valence copper(I,II) complexes. Hydration of nitrite solvents

Copper(II) acetate reacts with formaldehyde oxime (1 : 1) in a nitrite solvent, RCN at ca. 350 K to give a pale blue-green complex [Cu3(O2CMe)5(RCONH2)(CH2NOH)2](R = Me or Ph). The complex having R = Me reacts with acetic anhydride in acetonitrile to give CuCN, [Cu2(O2CMe)4(OH2)2], and [Cu2(CN)2(NCMe)], and with pyridine (py) to give [Cu(O2CMe)(CH2NOH)2], [Cu2(O2CMe)4(py)2], and acetamide.

Formamide as a precursor to cyanide in mixed-valence copper(I,II) cyanide complexes

Copper(I) acetate reacts with acetic anhydride–formamide (1 : 1) in acetonitrile solution to give [Cu2(O2CMe)(CN)] or [Cu2(CN)2(NCMe)]. Anhydrous copper(II) acetate reacts with the same reagent to give [Cu(NCMe)4][Cu2(CN)4] and [Cu(O2CMe)2(HCONH2)]. The influence of various polar solvents on the products of the reaction is evaluated. The complex [Cu(NCMe)4)][Cu2(CN)4] reacts with unidentate nitrogen-donor ligands, L, to form [CuL4][Cu2(CN)4](L = pyridine or 4-methylpyridine) or [CuL3][Cu2(CN)4](L = 2-methylpyridine or 2,6-dimethylpyridine). With bidentate nitrogen-donor ligands, L–L, substitution in [Cu(NCMe)4][Cu2(CN)4] gives [Cu(L–L)2(NCMe)][Cu2(CN)4](L–L = 1,2-diaminoethane or 2,2′-bipyridine). The insoluble complex products are obtained in good yield and characterized by microanalysis and spectroscopy (i.r. and visible reflectance). The role of copper ions in promoting the dehydration of formamide by acetic anhydride is assessed.

The copper-promoted reaction of o-halogenodiarylazo-compounds with nucleophiles. Part 3. The copper-promoted reaction of o-bromodiarylazo-compounds with carboxylate ions. A novel method for the preparation of o-hydroxydiarylazo-compounds

o-Bromo-o′-acetylaminodiarylazo-compounds react with potassium acetate in the presence of copper(II) acetate in Bipolar aprotic solvents to give the copper(II) complex of the corresponding o-hydroxy-o′-acetylaminodiarylazo-compounds in good yield. The reaction proceeds via the intermediate o-acetoxy-o′-acetylaminodiarylazo-compound which undergoes facile, in situ, copper-promoted hydrolysis. When the diarylazo-compound contains two o-bromine atoms only one is replaced, with a single exception.