A convenient one-pot synthesis of homoallylic halides and 1,3-butadienes

An efficient one-pot synthetic pathway for the preparation of homoallylic halides by in situ generated MgBrCl-promoted ring opening of cyclopropylcarbinyl acetates has been established. An easily accessible one-pot synthetic protocol of 1,3-butadienes by the elimination of hydrogen halides from the resulting homoallylic halides in the presence of an excess amount of strong base has also been developed.     

Synthesis of new polyazines by 1,4 photochemical or anionic polymerization of 1,2-diaza-1,3-butadienes

Photochemical and anionic polymerizations of 1,2-diaza-1,3-butadienes are described. Photochemical polymerization was smoothly performed by irradiation of some 1-aminocarbonyl-1,2-diaza-1,3-butadienes with high pressure mercury arc (λ = 300 nm) in the presence of allyltributylstannane. Molecular weights (M_w) in the range 14.6-559 × 10² g/mol were obtained. The TGA curve revealed a first weight loss starting at about 200 °C of some 85%, and a second starting at about 300 °C. The DSC showed the glass transition (T_g) at about −34 °C. Anionic polymerization was performed by treatment of some 1-alkoxycarbonyl-1,2-diaza-1,3-butadienes with n-butyllithium. Molecular weights (M_w) in the range 8.44-242 × 10² g/mol were obtained.     

Divergent intramolecular reactions between phosphines and alkynes

A divergent intramolecular reaction of phosphine tethered alkyne in protic solvent was developed.This provided a novel and simple access to a large variety of(Z)-alkenylphosphine oxides and phospholane oxides.Our preliminary studies suggested that these divergent reactions are closely related to the reaction condition and molecular structure.A possible mechanism of C-P bond cleavage of a pentacoordinated hydroxyphosphorane intermediate was proposed.     

Synthesis of stereo-defined 1,1,4,4-tetrahalo- and 1,1,4,4-mixed-tetrahalo-1,3-butadienes

Stereo-defined 1,1,4,4-tetrahalo- and 1,1,4,4-mixed-tetrahalo-1,3-butadienes were obtained in excellent yields via desilylation-halogenation of their corresponding 1,4-bis(trimethylsilyl)-1,4-dihalo-1,3-dienes, which could be readily prepared from the zirconocene-mediated high-yield and high-regioselective cyclo-dimerization of 1-trimethylsilyl-1-alkynes followed by halogenation. These poly-functionalized gem-dihalodienes are potentially useful building blocks.     

Stereoselective intramolecular hetero Diels-Alder reactions of 1-oxa-1,3-butadienes: a novel approach for the synthesis of complex annulated uracils

The intramolecular hetero Diels-Alder reactions of 1-oxa-1,3-butadienes 4, obtained from salicylaldehyde 1 via O-allylation followed by Knoevenagel condensation with barbituric acids 3 in the presence of hydrochloric acid as catalyst, affords the tetracyclic uracil derivatives 5 and 6 in a stereoselective manner and high overall yields.     

New route synthesis of indolizines via 1,3-dipolar cycloaddition of pyridiniums and alkynes

A convenient synthesis of 2,3-di and 1,2,3-trisubstituted indolizines has been achieved via a 1,3-dipolar cycloaddition of pyridiniums and alkynes. Various alkynes and diynes were used instead of dimethyl acetylenedicarboxylate (DMAD) and its analogues in the traditional method. The corresponding 1,2,3-trisubstituted indolizines are useful building blocks for the construction of complex indolizine derivatives.     

Synthesis and reactions of the first fluoroalkylated 1,3-bis(trimethylsilyloxy)-1,3-butadienes

The first fluoroalkylated 1,3-bis(silyloxy)-1,3-butadienes have been prepared. Their reaction with oxalyl chloride provides a convenient approach to fluoroalkylated γ-alkylidenebutenolides.     

Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl₂), bromine (Br₂) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl₂ and Br₂ with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.     

New diruthenium vinyliminium complexes from the insertion of alkynes into bridging aminocarbynes

Primary alkynes R′CCH [R′ = Me₃Si, Tol, CH₂OH, CO₂Me, (CH₂)₄CCH, Me] insert into the metal-carbon bond of diruthenium μ-aminocarbynes [Ru₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] [R = 2,6-Me₂C₆H₃ (Xyl), 1a; CH₂Ph (Bz), 1b; Me, 1c] to give the vinyliminium complexes [Ru₂{μ-η¹:η³-C(R′)CHCN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] [R = Xyl, R′ = Me₃Si, 2a; R = Bz, R′ = Me₃Si, 2b; R = Me, R′ = Me₃Si, 2c; R = Xyl, R′ = Tol, 3a; R = Bz, R′ = Tol, 3b; R = Bz, R′ = CH₂OH, 4; R = Bz, R′ = CO₂Me, 5a; R = Me, R′ = CO₂Me, 5b; R = Xyl, R′ = (CH₂)₄CCH, 6; R = Xyl, R′ = Me, 7a; R = Bz, R′ = Me, 7b; R = Me, R′ = Me, 7c]. The related compound [Ru₂{μ-η¹:η³-C[C(Me)CH₂]CHCN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃], (9) is better prepared by reacting [Ru₂{μ-CN(Me)(Xyl)}(μ-CO)(CO)(Cl)(Cp)₂] (8) with AgSO₃CF₃ in the presence of HCCC(Me)CH₂ in CH₂Cl₂ at low temperature.In a similar way, also secondary alkynes can be inserted to give the new complexes [Ru₂{μ-η¹:η³-C(R′)C(R′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = Bz, R′ = CO₂Me, 11; R = Xyl, R′ = Et, 12a; R = Bz, R′ = Et, 12b; R = Xyl, R′ = Me, 13). The reactions of 2-7, 9, 11-13 with hydrides (i.e., NaBH₄, NaH) have been also studied, affording μ-vinylalkylidene complexes [Ru₂{μ-η¹:η³-C(R′)C(R″)C(H)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (R = Bz, R′ = Me₃Si, R″ = H, 14a; R = Me, R′ = Me₃Si, R″ = H, 14b; R = Bz, R′ = Tol, R″ = H, 15; R = Bz, R′ = R″ = Et, 16), bis-alkylidene complexes [Ru₂{μ-η¹:η²-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (R′ = Me₃Si, R″ = H, 17; R′ = R″ = Et, 18), acetylide compounds [Ru₂{μ-CN(Me)(R)}(μ-CO)(CO)(CCR′)(Cp)₂] (R = Xyl, R′ = Tol, 19; R = Bz, R′ = Me₃Si, 20; R = Xyl, R′ = Me, 21) or the tetranuclear species [Ru₂{μ-η¹:η²-C(Me)CCN(Me)(Bz)}(μ-CO)(CO)(Cp)₂]₂ (23) depending on the properties of the hydride and the substituents on the complex. Chromatography of 21 on alumina results in its conversion into [Ru₂{μ-η³:η¹-C[N(Me)(Xyl)]C(H)CCH₂}(μ-CO)(CO)(Cp)₂] (22). The crystal structures of 2a[CF₃SO₃] · 0.5CH₂Cl₂, 12a[CF₃SO₃] and 22 have been determined by X-ray diffraction studies.     

Regioselective synthesis of fluoroalkyl pyridine derivatives from 3-fluoroalkyl substituted 2-aza-1,3-butadienes

A method for the preparation of 3-fluoroalkyl substituted 2-aza-butadienes by aza-Wittig reaction of N-vinylic phosphazenes and aldehydes is reported. [4+2] Cycloaddition reaction with enamines affords fluoralkyl substituted pyridine derivatives in a regioselective fashion.     

A molecular orbital study of the rotation about the C-C bond in 1,3-butadiene

The geometry and energy of 1,3-butadiene have been calculated using the 6-311G** basis set as a function of the CCCC dihedral angle-0 ° (trans), 30 °, 60 °, 75 °, 90 °, 120 °, 135 °, 150 °, 165 ° and 180 ° (cis)-assuming that the vinyl groups remain planar. Potential minima are located at 0 ° and 141.4 °, with the trans structure more stable than the gauche by 13.2 kJ mol^–1. Potential maxima are located at 76.7 °, giving a barrier height of 25.4 kJ mol^–1 relative to the trans structure, and at 180 ° giving a barrier height of 3.0 kJ mol^–1 relative to the 141.4 °-gauche structure. Using the 6-31G* basis set the inclusion of electron correlation, accounting for about 52% of the correlation energy, was found to produce no significant change in the shape of the potential energy curve. The magnitude of the expectation energy differences is such that both barriers with respect to the 14l.4 °-gauche maximum structure can be categorized unequivocally as attractive-dominant, whereas the values for the energy barrier with respect to the trans structure, although characteristic of a repulsive-dominant barrier at the 6–311G** level, are sufficiently small that higher level calculations might give the opposite result. Analysis of V _nn for the conversion reactions cis 150 °-gauche, trans 60 °-gauche, and trans 90 °-gauche in terms of the individual contributions from the various internuclear interactions shows that nonbonded interactions are important, not only in initiating the destabilization of the crowded cis structure, but also through-out the entire range of CCCC dihedral angles, 0 ° to 180 °.     

Synthesis of triazole-functionalized tetrahydroindazolones by 1,3-dipolar cycloadditions between azides and alkynes

7-Azido-tetrahydroindazolones undergo efficient copper-catalyzed Huisgen 1,3-dipolar cycloaddition reactions with various alkynes leading to a straightforward synthesis of triazole-functionalized tetrahydroindazolones. The latter are interesting molecular platforms in terms of medicinal chemistry.     

New Approach to the Synthesis of 1,3-Chloroisothiocyanatoalkanes. Synthesis of Tetrahydro-1,3-thiazine-2-thiones and 2-Alkylamino-5,6-dihydro-1,3-thiazines

A method was developed to prepare 1,3-chloroisothiocyanatoalkanes by reducing 1,3-isothiocyanato ketones using sodium borohydride at pH ~7 and subsequent treatment of the resultant 1,3-isothiocyanato alcohols with thionyl chloride. The reaction of 1,3-chloroisothiocyanatoalkanes with sodium hydrosulfide or amines gives substituted tetrahydro-1,3-thiazine-2-thiones or 2-amino-5,6-dihydro-1,3-thiazines.     

Tributylphosphine as a superior catalyst for the α-C-addition of 1,3-dicarbonyl compounds to electron-deficient alkynes

The present work describes an improved one pot access to α-(gem-difunctional) cinnamate esters and to conjugated 1,3-diketones exploiting the addition of 1,3-diketones, β-keto esters and malonates to alkynoates catalyzed by phosphines. Among the catalysts, nBu₃P was found as one of the most effective allowing the reaction to proceed in milder conditions and in a more general manner than with other phosphines.     

Synthesis of functionalized siloles from Si-tethered diynes

A new synthetic itinerary to silole from Si-tethered diynes is reported. In this protocol, the Si-tethered diyne manifests definitely the reactivity of monoyne to form the lithio silole via zirconacyclopetadiene, 1,4-diiodo-1,3-butadiene, and the corresponding dilithiodiene successively. Lithio siloles thus obtained above could be easily functionalized to give various types of silole derivatives. Complex structure like bridged bis-silole compounds could also be constructed by this process.     

Synthesis of Novel Thioethers from Polyhalobutadienes and Thiols

Abstract

Substituted perchlorobutadienes were synthesized from the reactions of hexachloro-1,3-butadiene with some thiols in ethanol in the presence of sodium hydroxide. The oxidation products were obtained from the reactions of thioethers with m-chloroperbenzoic acid. The structures of the new compounds were characterized by microanalysis and spectroscopic data.

GRAPHICAL ABSTRACT      

Synthesis and polymerization of 1- and 2-cyano-1,3-butadienes

1-Cyano-1,3-butadiene and 2-cyano-1,3-butadiene were prepared and designated 1-cyanoprene and 2-cyanoprene, respectively. These compounds, and their intermediates, were characterized by their infrared and proton magnetic resonance spectra. Their polymerizations with lithium or aluminum alkyl catalysts are described. The synthesis of these monomers involves a thermal cracking process (400–500°C). The yield of monomer by this process depends on the positions of the cyano and acetoxy groups in the butene intermediate; if the cyano and the acetoxy groups are attached to the same allylic carbon, a low monomer yield is obtained. The polymers of 1-cyanoprene are the results of 1,4-enchainment (cis and trans) and are amorphous; the polymers of 2-cyanoprene may involve 1,4-enchainment but are partially crystalline. Both of these polymers are thermoplastic.