Access to macrocyclic endocyclic and exocyclic allylic alcohols by nickel-catalyzed reductive cyclization of ynals

Ni-catalyzed reductive macrocyclizations of ynals are reported. Disubstituted alkynes afford either endocyclic or exocyclic allylic alcohols depending on the ligand. Phosphine ligands favor the formation of endocyclic olefins, whereas N-heterocyclic carbene ligands favor the formation of exocyclic olefins. Terminal alkynes provide 1,2-disubstituted olefins with N-heterocyclic carbene ligands.     

Enamines a halogene allylique—II: Action des organometalliques

In the condensation of organometallic reagents (Mg, Li, Cu) with halogenated enamines, there is a competition between substitution of the allylic halogen and rearrangement with loss of halogen, to give bicyclic compounds3 (6-pyrrolidino 6-alkyl bicyclo [3.1.0] hexanes). The reaction can be oriented toward the formation of the α-substituted ketone or of the bicyclic amine by an appropriate choice of the organometallic derivative, of the solvent and of the amino group of the enamine. The structure of the bicyclic amine3 could be the result of a selective attack on the least hindered side of the postulated intermediate immonium.     

Oxidation of alcohols by “activated” dimethyl sulfoxide. a preparative,steric and mechanistic study

The oxidation of primary, secondary, allylic, benzylic, hindered and bicyclic alcohols with dimethyl sulfoxide (DMSO) “activated” by numerous electrophiles was studied: yields of carbonyls, by-products and recovered alcohols were quantitatively determined. Pathways for carbonyl and by-product formation are presented. Generally, yields of carbonyls increase with increased steric hindrance in the alcohols. Steric effects of tertiary amines, used for basification, were also investigated, and the results are consistent with the suggested reaction pathways. Among previously unreported “activators,” oxalyl chloride is the most generally effective; yields of carbonyls are typically over 95%. Thionyl chloride is also a satisfactory “activator” although yields of carbonyls are not quite as high. An improved method of preparation of alkyl methylthiomethyl ethers, by-products of the oxidation process, is reported.     

Polybutadiene Modification: Reactions of Halogen-Containing Polybutadienes with Organolithium Compounds

Polybutadiene (PB) can be easily halogenated by reaction with iodine chloride or bromine in tetrahydrofuran. The resulting glassy polymers were reacted with n-butyllithium, sec-butyl-lithium, and polystyryllithium in THF. Iodochlorinated PB gave a polybutadiene with a different cis/trans ratio with n-BuLi. The reformation of PB was accompanied by partial crosslinking. The reaction probably involved a halogen-metal exchange followed by intra- and intermolecular elimination of Li halide. With brominated PB, both coupling and elimination took place. With sec-BuLi, an allylic iodine derivative was obtained from iodochlorinated PB, probably by dehydrochlorination. The iodinated intermediate can easily undergo a coupling reaction with further sec-BuLi. Both iodochlorinated and brominated polybutadienes gave graft copolymers by reaction with polystyryllithium in THF. Grafting was always accompanied by gel formation.     

Preparation of Polyfunctionalized Aromatic Nitriles from Aryl Oxazolines

A selective ortho,ortho’-functionalization of readily available aryl oxazolines by two successive magnesiations with sBu₂Mg in toluene followed by trapping reactions with electrophiles, such as (hetero)aryl iodides or bromides, iodine, tosyl cyanide, ethyl cyanoformate or allylic bromides (39 examples, 62–99 % yield) is reported. Treatment of these aryl oxazolines with excess oxalyl chloride and catalytic amounts of DMF (50 °C, 4 h) provided the corresponding nitriles (36 examples, 73–99 % yield). Conversions of these nitriles to valuable heterocycles are reported, and a tentative mechanism is proposed.     

Dimethyl sulfoxide/oxalyl chloride: A useful reagent for sulfenyletherification

A facile method for the sulfenyletherification of unsaturated alcohols using dimethyl sulfoxide/oxalyl chloride has been described in this article. Methanesulfenyl chloride is supposed to be the compound responsible for the sulfenyletherification, which is generated by the reaction of oxalyl chloride with 2 equivalents of dimethyl sulfoxide. The formation pathway of methanesulfenyl chloride is discussed based on the formation of cyclic acetals.     

Determination of the Absolute Configuration of a Series of Halogenated Furanones from the marine alga delisea pulchra

The absolute configuration of a series of naturally occurring and semi-synthetic halogenated furanones is proposed on the basis of chemical interconversions and X-ray and CD analyses. The CD analyses clearly reveal that the presence of the allylic O-atom has a strong influence in determining the sign and intensity of the low energy π→π* transition.     

Synthesis of Polysubstituted Iodoarenes Enabled by Iterative Iodine‐Directed para and ortho C−H Functionalization

Among halogenated aromatics, iodoarenes are unique in their ability to produce the bench‐stable halogen(III) form. Earlier, such iodine(III) centers were shown to enable C?H functionalization ortho to iodine via halogen‐centered rearrangement. The broader implications of this phenomenon are explored by testing the extent of an unusual iodane‐directed para C?H benzylation, as well as by developing an efficient C?H coupling with sulfonyl‐substituted allylic silanes. Through the combination of the one‐shot nature of the coupling event and the iodine retention, multisubstituted arenes can be prepared by sequentially engaging up to three aromatic C?H sites. This type of iodine‐based iterative synthesis will serve as a tool for the formation of value‐added aromatic cores.     

Mesyloxy-group migration as the stereoselective preparation method of various functionalized olefins and its reaction mechanism

[structure: see text]. It was demonstrated that mesylation of appropriate gamma,gamma-difluorinated allylic alcohols under usual conditions furnished the corresponding alpha,alpha-difluorinated allylic mesylates, possibly by way of 1,3-mesyloxy-group migration after formation of the expected "normal" intermediates, gamma,gamma-difluorinated allylic mesylates. This rearrangement was conveniently applied to the construction of trisubstituted allylic alcohols, alpha,beta-unsaturated esters, amides, or ketones in good to excellent chemical yields with exclusive E selectivities.     

Acylation of α-SCF3 substituted β-carbonyl acetic acid and thiacetic acid derivatives with oxalyl chloride

α-CF₃S-substituted β-ketoacidamides, nitriles, thioamides and their Schiff bases are synthesised and their reactions with oxalyl chloride are investigated. As a new phenomenon the elimination of the CF₃S group during cylcisation to substituted 2,3,5-trioxo-1,4-oxazephine (7), 4-pyrroline-2,3-dione (9) and oxalyl (10) is observed. Factors influencing this course of the reaction and mechanism of product formation are discussed.     

Complementary Iron(II)‐Catalyzed Oxidative Transformations of Allenes with Different Oxidants

Substituent‐ and oxidant‐dependent transformations of allenes are described. Given the profound influence of the substituent on the reactivity of allenes, the subtle differences in allene structures are manifested in the formation of diverse products when reacted with different electrophiles/oxidants. In general, reactions of nonsilylated allenes involve an allylic cation intermediate by forming a C?O bond, at the sp‐hybridized C2, with either DDQ (2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone) or TBHP (tert‐butyl hydroperoxide), along with FeCl₂?4 H₂O (10 mol %). In contrast, silylated allenes favor the formation of propargylic cation intermediates by transferring the allenic hydride to the oxidant, thus generating 1,3‐enynes (E1 product) or propargylic THBP ethers (S_N1 product). The formation of these different putative cationic intermediates from nonsilylated and silylated allenes is strongly supported by DFT calculations.     

Mixed disproportionation versus radical trapping in titanocene(III)-promoted epoxide openings

The formation of either deoxygenation products or allylic alcohols from epoxides is observed when these substrates are treated with Cp₂TiCl under anhydrous conditions. It seems that processes via trisubstituted radicals give allylic alcohols whereas processes via disubstituted radicals may give deoxygenation products or allylic alcohols depending on the structure of the original epoxide. This method allows a controlled access to these functional groups, providing a useful tool in organic synthesis. A mechanistic discussion for these transformations is reported.     

Regioselective allylic alkylation and etherification catalyzed by in situ generated N-heterocyclic carbene ruthenium complexes

Benzimidazolium halides are used for the first time as ligand precursors in ruthenium-catalyzed substitution of allylic carbonates and chlorides by carbon nucleophiles and phenols, respectively. After generation of diaminocarbene species upon deprotonation by tBuOK, their association with [Cp*Ru(MeCN)₃]PF₆ induces a very high regioselectivity in favor of the branched isomers when cinnamyl derivatives are used as starting substrates. They also provide good regioselectivities for the allylation of phenols by unsymmetrical aliphatic allylic substrates such as 3-chloro-4-phenylbut-1-ene, and thus provide a straightforward access to new allylic phenyl ethers.     

Photochemical grafting and activation of organic layers on glassy carbon and pyrolyzed photoresist films

Organic films have been grafted to polished glassy carbon (GC) and as-prepared pyrolyzed photoresist film (PPF) by photolysis of alkenes and an alkyne. The alkene or alkyne is spin-coated onto the carbon surface and photolyzed in air at 254 nm. Characterization by water contact angle measurements, depth profiling and surface roughness measurements using atomic force microscopy (AFM), and electrochemistry reveal that for most modifiers a loosely packed monolayer is grafted to the surface. Grafted layers of 1-decene were further reacted by drop-coating with oxalyl chloride and photolyzing at 254 nm in air. The procedure adds acid chloride groups to the film. Amines were attached to these films via amide bond formation, and were characterized by electrochemistry and assembly of citrate-capped gold nanoparticles. Amines were also coupled to photografted 1-undecylenic acid layers and to carboxyphenyl layers prepared by electroreduction of the corresponding diazonium salt. Quantitative analysis using electrochemistry established that the highest concentration of amines was attached to the oxalyl chloride treated film, and that a higher concentration of amines was attached via reaction with the photografted 1-undecylenic acid layer than the electrografted carboxyphenyl layer. Thus photografting and photoreaction with oxalyl chloride are simple methods for generating amine-reactive tethers on GC and PPF surfaces.     

Selective Halogenation Using an Aniline Catalyst

Electrophilic halogenation is used to produce a wide variety of halogenated compounds. Previously reported methods have been developed mainly using a reagent‐based approach. Unfortunately, a suitable “catalytic” process for halogen transfer reactions has yet to be achieved. In this study, arylamines have been found to generate an N‐halo arylamine intermediate, which acts as a highly reactive but selective catalytic electrophilic halogen source. A wide variety of heteroaromatic and aromatic compounds are halogenated using commercially available N‐halosuccinimides, for example, NCS, NBS, and NIS, with good to excellent yields and with very high selectivity. In the case of unactivated double bonds, allylic chlorides are obtained under chlorination conditions, whereas bromocyclization occurs for polyolefin. The reactivity of the catalyst can be tuned by varying the electronic properties of the arene moiety of catalyst.     

Reactivity, chemoselectivity, and diastereoselectivity of the oxyfunctionalization of chiral allylic alcohols and derivatives in microemulsions: comparison of the chemical oxidation by the hydrogen peroxide/sodium molybdate system with the photooxygenation

The chiral allylic alcohols 1a-d and their acetate (1e) and silyl ether (1f) derivatives have been oxidized by the H2O2/MoO4(2)- system, a convenient and efficient chemical source of singlet oxygen. This chemical peroxidation (formation of the allylic hydroperoxides 2) has been conducted in various media, which include aqueous solutions, organic solvents, and microemulsions. The reactivity, chemoselectivity, and diastereoselectivity of this chemical oxidation are compared to those of the sensitized photooxygenation, with the emphasis on preparative applications in microemulsion media. While a similar threo diastereoselectivity is observed for both modes of peroxidation, the chemoselectivity differs significantly, since in the chemical oxidation with the H2O2/MoO4(2)- system the undesirable epoxidation by the intermediary peroxomolybdate competes efficiently with the desirable peroxidation by the in situ generated singlet oxygen. A proper choice of the type of microemulsion and the reaction conditions furnishes a high chemoselectivity (up to 97%) in favor of threo-diastereoselective (up to 92%) peroxidation.     

Synthesis and nucleophilic substitution of stable 6-halo-pentafulvenes

The reaction of 2,4-di-t-butyl-cyclopentadiene-1-carbaldehyde with oxalyl chloride or oxalyl bromide provides stable 6-chloro- and 6-bromo-pentafulvenes, respectively. Several nucleophilic displacement reactions of the new compounds are described.     

Synthesis of nearly enantiopure allylic amines by aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates catalyzed by highly active ferrocenylbispalladacycles

The development of the first highly active enantioselective catalyst for the aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates generating valuable almost enantiopure protected allylic amines is described. Usually Z-configured allylic imidates react significantly slower than their E-configured counterparts, but in the present study the opposite effect was observed. Z-Configured olefins have the principal practical advantage that a geometrically pure C=C double bond can be readily obtained, for example, by semihydrogenations of alkynes. Our catalyst, a C(2)-symmetric planar chiral bispalladacycle complex, is rapidly prepared from ferrocene in four simple steps. Key step of this protocol is an unprecedented highly diastereoselective biscyclopalladation providing dimeric macrocyclic complexes of fascinating structure. In the present study as little as 0.1 mol % of catalyst precursor were sufficient for most of the alkyl substituted substrates to give in general almost quantitative yields. NMR investigations revealed a monomeric structure for the active catalyst species. The bispalladacycle can also be used for the formation of almost enantiomerically pure allylic amines (ee > or =96 %) substituted with important functional groups such as ester, ketone, ether, silyl ether, acetal or protected amino moieties providing high-added-value allylic amine building blocks in excellent yield (> or =94 %). The preparative advantages should render this methodology highly appealing as a practical and valuable tool for the formation of allylic amines in target oriented synthesis.     

Palladium(II)-catalyzed cycloisomerization of substituted 1,5-hexadienes: a combined experimental and computational study on an open and an interrupted hydropalladation/carbopalladation/β-hydride elimination (HCHe) catalytic cycle

The Pd(II)-catalyzed cycloisomerization of 3-alkoxycarbonyl-3-hydroxy-substituted 1,5-hexadienes has been studied experimentally and computationally. Experimentally, the reaction is characterized by a rapid room temperature formation of monomeric as well as dimeric cycloisomerization products using the commercially available precatalyst [(CH(3)CN)(4)Pd](BF(4))(2). In situ NMR measurements indicate the initial kinetic advantage of the desired cycloisomerization pathway to methylene cyclopentanes; however, double bond isomerization, elimination, and dimer formation are competitive undesired pathways. Evaluation of the obtained product structures by NMR spectroscopy and X-ray crystallography indicates that the sole determinant for the monomer/dimer ratio is the regioselectivity of the initial hydropalladation in favor of the allylic (monomer formation) or the homoallylic double bond (dimer formation). In order to account for the experimental results, we propose the coexistence of two product-forming catalytic cycles, an open, monomer generating, as well as an interrupted and redirected, dimer generating, hydropalladation/carbopalladation/β-hydride elimination (HCHe) process. Results from computational studies of the proposed competing catalytic cycles are supportive to our mechanistic hypothesis and pinpoint the pivotal importance of Pd(II)-hydroxo-chelate complexes for the reactivity-stability interplay of on- and off-pathway intermediates.     

C-N bond cleavage of allylic amines via hydrogen bond activation with alcohol solvents in Pd-catalyzed allylic alkylation of carbonyl compounds

Hydrogen-bond-activated C-N bond cleavage of allylic amines was realized in Pd-catalyzed allylic alkylation to form the C-C bond product. The method could be expanded to a series of allylic amines and carbonyl compounds with excellent results. It provides a new and convenient access to C-C bond formation based on Pd-catalyzed allylic alkylation of allylic amines by using only inexpensive alcohol solvents.