Triethylaluminum- or triethylborane-induced free radical reaction of alkyl iodides and alpha,beta-unsaturated compounds

A series of alpha,beta-unsaturated compounds, 1a-c, 9, 13, and 17, were used as reactants in free radical conjugate addition reactions with different radicals generated from alkyl iodides such as 3, 4, or 5 in the presence of triethylborane-oxygen in air or via the use of triethylaluminum-benzoyl peroxide as a free radical initiator. When the reactions were carried out using triethylborane-air, the products, in most cases, were clean and were easily purified. However, higher yields of the 1,4-adducts and less side reactions occurred when less reactive substrates were used as Michael acceptors in reactions with triethylaluminum-benzoyl peroxide and alkyl iodide under similar conditions. A mechanism for this is proposed in Scheme 1.     

Palladium-catalyzed Heck-type reactions of alkyl iodides

A palladium-catalyzed Heck-type reaction of unactivated alkyl iodides is described. This process displays broad substrate scope with respect to both alkene and alkyl iodide components and provides efficient access to a variety of cyclic products. The reaction is proposed to proceed via a hybrid organometallic-radical mechanism, facilitating the Heck-type process with alkyl halide coupling partners. Initial intermolecular studies are also reported, demonstrating the potentially wide applicability of this approach in synthesis.     

Reactivity of alkyl iodides in molecular decomposition reactions

The experimental results for the concerted molecular decomposition of alkyl iodides RI to olefin and HI were analyzed in terms of the intersecting parabolas model (IPM). The activation energies (E) and rate constants (k) of the earlier unstudied reactions of the concerted molecular decomposition of RI were calculated on the basis of the enthalpy of the reaction and IPM algorithms. The factors that influence on E of RI decay were established: the enthalpy of the reaction, the energy of stabilization of radical R*, the length and force constant of the C—I bond, and the size of the halogen atom. The values of E and k for the backward reactions of HI addition to olefins were estimated.     

Conversion of alcohols into alkyl bromides and iodides via O-alkylisoureas

Treatment of O-alkylisoureas with trifluoromethanesulphonic acid and a tetrabutylammonium salt (bromide or iodide) affords alkyl halides in high yields.     

Cross-couplings of unactivated secondary alkyl halides: room-temperature nickel-catalyzed Negishi reactions of alkyl bromides and iodides

The development of a nickel- or palladium-catalyzed method for cross-coupling unactivated secondary alkyl halides has been a long-standing challenge in synthetic chemistry. This communication describes a simple catalyst system-Ni(cod)2/s-Bu-Pybox-that achieves room-temperature Negishi reactions of an array of functionalized primary and secondary alkyl bromides and iodides.     

Simple synthesis of fresh alkyl iodides using alcohols and hydriodic acid

A simple synthesis of fresh alkyl iodides using alcohols and hydriodic acid (HI) is reported. The alkyl iodides were obtained in quick and easy work-up with good to excellent yields (66-94%) and very high purities (97-99%). Freshly prepared iodomethane and 1-iodobutane were applied to synthesize biologically relevant 3,7-dimethyladenine and 9-butyladenine, which were characterized thoroughly using 1D and 2D NMR, individually.     

Novel amine-catalysed hydroalkoxylation reactions of activated alkenes and alkynes

Substoichiometric loadings of DBU catalyse the efficient 1,4-addition of alcohols and non-nucleophilic amines such as pyrrole to activated alkenes; the application of this methodology in a one-pot synthesis of a natural product, and as a novel strategy for the synthesis of mono-protected 1,3-carbonyl compounds is reported.     

Stereoselective synthesis of dibenzoxapine containing tetrasubstituted exocyclic alkenes via cascade methylboronic acid coupling reactions

A stereoselective method for the preparation of dibenzoxapine containing tetrasubstituted exocyclic E-alkenes has been developed. The key reaction involves an intramolecular cyclocarbopalladation of alkynes to form a vinylpalladium species and subsequently coupling the vinylpalladium with methylboronic acid. The approach provides a straightforward method for the synthesis of tetrasubstituted exocyclic E-alkenes.     

The first applications of carbene ligands in cross-couplings of alkyl electrophiles: sonogashira reactions of unactivated alkyl bromides and iodides

A Pd/N-heterocyclic carbene-based catalyst achieves the Sonogashira coupling of an array of functionalized, beta-hydrogen-containing alkyl bromides and iodides under mild conditions. By furnishing the first example of a nonphosphine-based palladium catalyst for cross-coupling unactivated alkyl electrophiles, this study provides an impetus for future efforts at catalyst development that extend beyond phosphine ligands.     

Two-photon MPI spectroscopy of alkyl iodides

The two-photon resonant multiphoton ionization (MPI) spectra of methyl iodide, methyl iodide-d₃, ethyl, propyl, and butyl iodide are reported in the 49 000-55 000 cm^?1 region. Four separate transitions to excited states labeled Δ, Π, Σ, Π in increasing energy are expected in this range which result from the excitation of an iodine 5pπ electron to the 6s molecular Rydberg orbital. Two-photon spectroscopy with its different selection rules and unique dependence on the laser polarization is shown to significantly advance the understanding of these transitions. In particular, laser polarization studies identify a state which is strongly two-photon allowed but absent in the UV absorption spectrum as the Σ state. Rotational contours indicate a large geometry change takes place in this transition. The two Π states appear strongly in both the one-and two-photon spectrum. Polarization analysis confirms their electronic symmetry assignment in addition to distinguishing vibronic bands arising from nontotally symmetric vibrations. No evidence is found for the Δ state in the multiphoton ionization spectrum, due to either a small two-photon cross section or a low probability of ionization following the initial two-photon transition. Further complications and characteristics of single laser MPI spectroscopy in the study of two-photon absorption in methyl iodide and other fundamental molecules are discussed.     

Rhodium-catalyzed triarylphosphine synthesis via cross-coupling of aryl iodides and acylphosphines

Rhodium(I)-catalyzed C–P cross-coupling reaction with aryl iodides and acylphosphines was disclosed for a straight forward synthesis of triarylphosphines. The acylphosphines were successfully employed as both the phosphorus source and the ligand to the Rh(I) catalyst. The triarylphosphines could be afforded in a yield up to 98% with good toleration of wide functional groups.     

Palladium-catalyzed negishi cross-coupling reactions of unactivated alkyl iodides, bromides, chlorides, and tosylates

A single method (2% Pd(2)(dba)(3)/8% PCyp(3)/NMI in THF/NMP at 80 degrees C; Cyp = cyclopentyl) achieves the cross-coupling of a range of beta-hydrogen-containing primary alkyl iodides, bromides, chlorides, and tosylates with an array of alkyl-, alkenyl-, and arylzinc halides. The process is compatible with a variety of functional groups, including esters, amides, imides, nitriles, and heterocycles.     

A facile synthesis of aryl iodides via potassium aryltrifluoroborates

Aryl- and heteroaryltrifluoroborates are rapidly converted to aryl and heteroaryl iodides under mild conditions using sodium iodide in the presence of mild oxidizing agents.     

Reactions of piroxicam with alkyl iodides

Alkylation of piroxicam with a homologous series of alkyl iodides gave reversibly formed O-alkyl products 1 as well as unexpected, irreversibly formed zwitterionic compounds 2 , alkylated on the pyridine nitrogen, and O,N-bis-alkyl products 3 . Proof of structure was accomplished by nmr and X-ray crystal analysis. Product distribution ratios were determined by hplc and are explained by the Hard-Soft Acid-Base principle.