Photochemical reactions of acyl iodides with aryl halides

Photochemical reactions of acyl iodides RC(O)I (R = Me, Ph) with aryl halides, fluoro-, chloro-, and bromobenzenes, 1,4-dibromobenzene, 2- and 3-bromotoluenes, and 4-bromo-1,2-dimethylbenzene, were studied. Acetyl iodide reacted with chloro- and bromobenzenes and 1,4-dibromobenzene according to the exchange pattern to give iodobenzene and 1,4-diiodobenzene, respectively. No halogen exchange was observed in the reactions of acetyl iodide with fluorobenzene and hexafluorobenzene. Benzoyl iodide failed to react with chloro- and brombenzene under UV irradiation but underwent polycondensation with formation of black nonfusible oligomers which were found to possess paramagnetic and semiconducting properties. Ultraviolet irradiation of a mixture of MeCOI with 2- or 3-bromotoluene, as well as with 4-bromo-1,2-dimethylbenzene, also led to the formation of polymeric products as a result of polycondensation of aryl iodides formed initially via replacement of bromine by iodine. Irradiation of benzoyl iodide in 2- or 3-bromotoluene involved recombination of benzoyl radicals to give benzil as the only product.     

Silver-catalyzed coupling reactions of alkyl halides with indenyllithiums

Coupling reactions of tertiary and secondary alkyl halides with indenyllithiums proceeded effectively in the presence of a catalytic amount of silver bromide to provide tertiary- and secondary-alkyl-substituted indene derivatives in good yields.     

Kumada-Corriu reactions of alkyl halides with alkynyl nucleophiles

[reaction: see text] Pd(2)(dba)(3)-Ph(3)P-catalyzed Kumada-Corriu coupling reactions of unactivated alkyl bromides or iodides with an alkynyl nucleophile furnish C(sp)-C(sp)3 bond formation. Alkynyl nucleophiles can be alkynyllithiums or the corresponding Grignard reagents. The superior performance of Ph(3)P ligand over the trialkylphosphine ligands indicates that this cross-coupling reaction may be a reductive-elimination-controlled process.     

Pd-catalyzed cross-coupling reactions of alkyl halides

Cross-coupling reactions have become indispensable tools for creating carbon-carbon (or heteroatom) bonds in organic synthesis. Like in other important transition metal catalyzed reactions, such as metathesis, addition, and polymerization, unsaturated compounds are usually employed as substrates for cross-coupling reactions. However during the past decade, a great deal of effort has been devoted to the use of alkyl halides as saturated compounds in cross-coupling reactions, which has resulted in significant progress in this undeveloped area by introducing new effective ligands. Many useful catalytic systems are now available for synthetic transformations based on C(sp(3))-C(sp(3)), C(sp(3))-C(sp(2)) and C(sp(3))-C(sp) bond formation as complementary methods to conventional C(sp(2))-C(sp(2)), C(sp(2))-C(sp) and C(sp)-C(sp) coupling. This tutorial review summarizes recent advances in cross-coupling reactions of alkyl halides and pseudohalides catalyzed by a palladium complex.     

Catalysts for cross-coupling reactions with non-activated alkyl halides

Despite the problems inherent to metal-catalyzed cross-coupling reactions with alkyl halides, these reactions have become increasingly important during the last few years. Detailed mechanistic investigations have led to a variety of novel procedures for the selective cross-coupling of non-activated alkyl halides bearing beta hydrogen atoms with a variety of organometallic nucleophiles under mild reaction conditions. This Minireview highlights selected examples of metal-catalyzed coupling methods and is intended to encourage chemists to exploit the potential of these approaches in organic synthesis.     

Reaction of bis(mercaptomethyl)phosphonic acid with alkyl and acyl halides

Conclusions The reactions of bis(mereaptomethyl)phosphonic acid with alkyl and acyl halides were studied and a series of new thiomethyl phosphorus derivatives was synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2388–2390, October, 1968.     

The rapid and efficient synthesis of disulfides from alkyl and acyl halides

Various symmetrical dialkyl and diacyl disulfides are prepared easily in high yields from the corresponding alkyl and acyl halides under mild and nonaqueous conditions using N,N′-dibutyl-N,N,N′,N′-tetramethyl-ethylenediammonium tetrahydroborate (BTMETB) or N,N′-dibenzyl-N,N,N′,N′-tetramethylethylenediammonium tetrahydroborate (BZTMETB) and elemental sulfur. The quaternary diammonium borohydrides were easily prepared by treatment of the corresponding quaternary diammonium chloride or bromide with alkaline solution of sodium borohydride at room temperature. Correspondence: Mahmood Tajbakhsh, Department of Chemistry, Mazandaran University, Babolsar, Iran.     

The rapid and efficient synthesis of disulfides from alkyl and acyl halides

Various symmetrical dialkyl and diacyl disulfides are prepared easily in high yields from the corresponding alkyl and acyl halides under mild and nonaqueous conditions using N,N′-dibutyl-N,N,N′,N′-tetramethyl-ethylenediammonium tetrahydroborate (BTMETB) or N,N′-dibenzyl-N,N,N′,N′-tetramethylethylenediammonium tetrahydroborate (BZTMETB) and elemental sulfur. The quaternary diammonium borohydrides were easily prepared by treatment of the corresponding quaternary diammonium chloride or bromide with alkaline solution of sodium borohydride at room temperature.     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with aryl Grignard reagents and their application to sequential radical cyclization/cross-coupling reactions

Reactions of alkyl halides with arylmagnesium bromides in the presence of cobalt(II)(diphosphine) complexes are discussed. Treatment of 1-bromooctane with phenylmagnesium bromide with the aid of a catalytic amount of CoCl₂(dppp) [DPPP=1,3-bis(diphenylphosphino)propane] yielded octylbenzene in good yield. The reaction mechanism would include single electron transfer from an electron-rich cobalt complex to alkyl halide to generate the corresponding alkyl radical. The mechanism was justified by CoCl₂(dppe)-catalyzed [DPPE=1,2-bis(diphenylphosphino)ethane] sequential radical cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives that yielded benzyl-substituted cyclopentane skeletons.     

Novel diborane-analogue transition structures for borane reactions with alkyl halides

Ab initio and DFT calculations were performed to examine the mechanisms of reduction of alkyl halides and formaldehyde by borane. With alkyl halides, the optimized transition structure geometry resembled diborane, with a pair of hydrogen atoms bridging the boron and carbon atoms by three-center-two-electron bonds. A similar transition structure was found for the reduction of formaldehyde, although it was not the lowest-energy transition structure. Solvation by dimethyl ether or dimethyl sulfide disrupted this bridging with chloromethane, while both ligands dissociated from borane during the reduction of formaldehyde. The high calculated activation free energies of alkyl halide reduction are consistent with their observed lack of reactivity with borane.     

Bridged cyclophosphazenes resulting from deprotonation reactions of cyclotriphophazenes bearing a P-NH group

Cyclotriphosphazene derivatives containing a P-NHR group in the side-chain react in the presence of a strong base to form stable intermolecular bridged products. Reaction of sodium hydride with mono-spiro cyclophosphazene derivatives having a P-NH group, N(3)P(3)Cl(4)[O(CH(2))(3)NH], (1a) or N(3)P(3)Cl(4)[CH(3)N(CH(2))(3)NH], (1b) leads to formation of bis-cyclophosphazenes bridged with an eight-membered cyclophosphazene ring in an ansa arrangement (2a, 2b) whereas reaction of sodium hydride with mono-amino cyclophosphazene derivatives [N(3)P(3)Cl(5)(NHR), R = n-hexyl, 3a; i-Pr, 3b; Ph, 3c] give bis-cyclophosphazenes bridged with a four-membered cyclophosphazane ring in a spiro arrangement (4a-c). In the latter reaction P-O-P bridged compounds (5a-c) were also obtained as a result of hydrolysis reactions associated with the amount of moisture in the solvent tetrahydrofuran. In addition, it was found that reaction of a mixture of cyclotriphosphazene with either mono spiro compound, (1a) or (1b), in the presence of sodium hydride lead to formation of the first examples of asymmetrically-bridged cyclophosphazenes (6a-b).     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic and benzylic Grignard reagents and their application to tandem radical cyclization/cross-coupling reactions

Details of cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic Grignard reagents are disclosed. A combination of cobalt(II) chloride and 1,2-bis(diphenylphosphino)ethane (DPPE) or 1,3-bis(diphenylphosphino)propane (DPPP) is suitable as a precatalyst and allows secondary and tertiary alkyl halides--as well as primary ones--to be employed as coupling partners for allyl Grignard reagents. The reaction offers a facile synthesis of quaternary carbon centers, which has practically never been possible with palladium, nickel, and copper catalysts. Benzyl, methallyl, and crotyl Grignard reagents can all couple with alkyl halides. The benzylation definitely requires DPPE or DPPP as a ligand. The reaction mechanism should include the generation of an alkyl radical from the parent alkyl halide. The mechanism can be interpreted in terms of a tandem radical cyclization/cross-coupling reaction. In addition, serendipitous tandem radical cyclization/cyclopropanation/carbonyl allylation of 5-alkoxy-6-halo-4-oxa-1-hexene derivatives is also described. The intermediacy of a carbon-centered radical results in the loss of the original stereochemistry of the parent alkyl halides, creating the potential for asymmetric cross-coupling of racemic alkyl halides.     

Radical reductions of alkyl halides bearing electron withdrawing groups with N-heterocyclic carbene boranes

1,3-Dimethylimidazol-2-ylidene borane and 2,4-dimethyl-1,2,4-triazol-3-ylidene borane are found to be useful reagents for the reduction of alkyl iodides and bromides bearing nearby electron withdrawing substituents. Signatures of radical chain reactions are seen in many cases, but ionic reductions may also be occurring with some substrates. The reagents are attractive because of their low molecular weight, their availability from inexpensive precursors, and their stability. Separation of the borane products from the target products is readily accomplished either with or without prior regeneration of the borane for later reuse. 2,4-Dimethyl-1,2,4-triazol-3-ylidene borane is versatile because both starting borane and its derived products can be removed by extraction with water.     

Silver-catalyzed benzylation and allylation reactions of tertiary and secondary alkyl halides with grignard reagents

Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers.     

Reaction of dialkyldithiotrimethylsilylphosphites with acyl halides

It has been established that S,S-dialkyltrimethylsilyldithiophosphites react with acyl halides in two directions, depending on the nature of the halogen in the acyl halide and on the reaction conditions, thus giving as the main reaction products either dialkyldithiohalophosphites or dialkyldithioacylphosphonates. The latter compounds react with acyl halides in accordance with a retro-Arbuzov reaction scheme, giving dialkyldithiohalophosphites.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, Kazan 420083. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 1011–1016, April, 1992.     

Simple iron-amine catalysts for the cross-coupling of aryl Grignards with alkyl halides bearing beta-hydrogens

Mixtures of iron(III) chloride and appropriate amine ligands are active catalysts for the coupling of aryl Grignard reagents with primary and secondary alkyl halide substrates bearing beta-hydrogens, under mild and simple reaction conditions.