1,4-Dihydro-1λ5,4λ5-[1,4]diphosphinine und ein 1,4-Dihydro-1λ3,4λ3-[1,4]diphosphinin

1,4-Dihydro-1λ⁵,4λ⁵-[1,4]diphosphinines and a 1,4-Dihydro-1λ³,4λ³-[1,4]diphosphinine Reaction of thio- or dithiocarbonic acids with ethinyl amino phosphanes leads to 1,4-dihydro-1λ⁵,4λ⁵-[1,4]diphosphinine-1,4-disulfides. By this route compounds 4, 7 , and 8 have been prepared. Desulfurization of 4 with tri-n-butylphosphane results in 1,2,4,5-tetraphenyl-1,4-dihydro-1λ³,4λ³-[1,4]-diphosphinine 5 , which can be oxidized with tert-butyl-peroxide to the corresponding dioxide, 6 . From the reaction mixture of phenyl-phenylethinyl diethylamino phosphane and thioacetamide compound 4 and the unsymmetrical 1,4-dihydro-1λ⁵,4λ⁵-[1,4]diphosphinine 9 were isolated. Properties, nmr, ir and mass spectra of all new products are reported. A mechanism for the formation of 9 is suggested. The results of the X-ray structure determination of 8 and 9 are described.     

Polyesters,polycarbonate, and polyurethanes from a novel monomer: α,α,α′,α′-tetramethyl-1,4-tetrafluorobenzenedimethanol

The novel diol monomer, α,α,α′,α′-tetramethyl-1,4-tetrafluorobenzenedimethanol, has been synthesized by a convenient route which involves the addition of acetone to 1,4-dilithiotetrafluorobenzene and can be purified by washing with hexanes. It does not directly undergo condensation polymerizations with diacid chlorides. Its disodium salt, prepared by its reaction with sodium hydride, similarly fails to undergo such polymerizations readily. However, the dilithium salt, prepared in situ by the reaction of the title diol with 2 equiv of n-butyllithium in tetrahydrofuran, is suitable for the preparation of various classes of condensation polymers. Four polyesters and one polycarbonate derived from the reactions of the dilithium salt of the diol with adipoly dichloride, sebacoyl dichloride, isophthaloyl dichloride, terephthaloyl dichloride, and phosgene and two polyurethanes derived from its reactions with tolylene-2,4-diisocyanate and methylene-di-1,4-phenyl diisocyanate were prepared. Each was fully characterized by GPC, NMR, IR, and UV-visible spectroscopies, and the results of these studies are reported herein. © 1993 John Wiley & Sons, Inc.     

Free-radical reactions of diazonium salts with α,β-unsaturated carbonyl compounds. A new synthesis of 1,4-diarylpyrazole derivatives

Free-radical decomposition of diazonium salts catalyzed by titanous or titanous and ferrous salts in the presence of β-substituted α,β-unsaturated carbonyl compounds leads to 1,4-diarylpyrazole derivatives. The reaction occurs via an intermediate azo compound ( 1 ), which can be reduced by the metal salt or can be isolated and hydrogenated to pyrazole derivatives.     

1,4‐Addition of Bis(iodozincio)methane to α,β‐Unsaturated Ketones: Chemical and Theoretical/Computational Studies

1,4‐Addition of bis(iodozincio)methane to simple α,β‐unsaturated ketones does not proceed well; the reaction is slightly endothermic according to DFT calculations. In the presence of chlorotrimethylsilane, the reaction proceeded efficiently to afford a silyl enol ether of β‐zinciomethyl ketone. The C? Zn bond of the silyl enol ether could be used in a cross‐coupling reaction to form another C? C bond in a one‐pot reaction. In contrast, 1,4‐addition of the dizinc reagent to enones carrying an acyloxy group proceeded very efficiently without any additive. In this case, the product was a 1,3‐diketone, which was generated in a novel tandem reaction. A theoretical/computational study indicates that the whole reaction pathway is exothermic, and that two zinc atoms of bis(iodozincio)methane accelerate each step cooperatively as effective Lewis acids.     

Rhodium‐Catalyzed Asymmetric Arylation of β,γ‐Unsaturated α‐Ketoamides for the Construction of Nonracemic γ,γ‐Diarylcarbonyl Compounds

A highly regio‐ and enantioselective rhodium‐catalyzed 1,4‐addition of arylboronic acids to β,γ‐unsaturated α‐ketoamides using a simple new chiral sulfinylphosphine ligand is described. This transformation provides an attractive approach to construct chiral nonracemic γ,γ‐diarylsubstituted carbonyl compounds, as exemplified in the concise syntheses of sertraline and tetrahydroquinoline‐2‐carboxylamide.     

Cyclisierung eines aluminiumorganischen 3-cumulen zum 1,4-dialuminacyclohexadien

1,4-Diethylaluminyl-1,4-diphenyl-3-cumulene gives on UV irradiation at 20°C or on heating to 90°C the 1,4-dialuminacyclohexadiene derivative. The cyclisation mechanism of this reaction is discussed.     

Enantioselective Copper-Catalyzed 1,4-Addition of Grignard Reagents to α,β-Unsaturated Carbonyl Compounds

The enantioselective copper-catalyzed 1,4-addition of Grignard reagents to α,β-unsaturated carbonyl compounds was studied with the following Cu^I compounds as catalyst precursor and 1,2:5,6-di-O-isopropylidene-3-thio-α-D -glucofuranose (Hsiig) as chiral ligand: CuI, iodo[bis(dibutylsulfide)]copper(I), [Cu(siig)], [Cu(siig)(pp)] (pp =1,2-bis)(diphenylphosphinoethene), and tetrakis[iodo(tributylphosphine)]copper(I). The addition of BuMg halides to cyclohex-2-en-1-one was tested under several reaction conditions. The chemical yields and regioselectivities for this reaction were, in all cases, larger than 90 and 98%, respectively, and independent of the experimental conditions. The enantioselectivity was strongly dependent on the reaction conditions and reached a maximum of 60%. Several other substrates were also tested in the above reaction. The X-ray crystal structure for [Cu(siig)(pp)] was determined by X-ray crystallography.     

Catalyst free synthesis of 2-Aryl-2H-benzo[b][1,4]oxazines and 3-Aryl-2H-benzo[b][1,4]thiazin-2-ones: An ultrasonication-assisted strategy

An ultrasonication-assisted synthesis of 2-Aryl-2H-benzo[b][1,4]oxazines and 3-aryl-2H-benzo[b][1,4]thiazin-2-ones has been established by reacting phenacyl bromides with 2-aminophenol and 2-aminothiophenol, respectively. This approach fosters flexibility in generating a diverse range of 1,4-benzoxazines and 1,4-benzothiazinones under catalyst-free reaction conditions. Further scope toward the synthesis of rarely occurring bis-benzoxazine adduct has also been explored, which enabled us to propose the reaction mechanism.     

Cobalt‐Catalyzed Formal [4+2] Cycloaddition of α,α′‐Dichloro‐ortho‐Xylenes with Alkynes

A formal [4+2] cycloaddition of α,α′‐dichloro‐ortho‐xylenes with various alkynes has been developed using a low‐valent cobalt catalyst. The transformation has a wide substrate scope and high functional‐group tolerance and led to 1,4‐dihydronaphthalenes. The formed cycloadducts were easily aromatized with MnO₂ under air. A mechanistic investigation suggests that the transformation proceeds through a benzyl cobaltation of alkyne, not the classical Diels–Alder reaction of ortho‐quinodimethanes. This methodology provides a straightforward and streamlined access to linearly expanded π‐conjugated aromatics.     

Radical polyaddition of bis(α-trifluoromethyl-β-difluorovinyl) terephthalate with 1,4-dioxane

To develop a radical polyaddition reaction of 2-benzoyloxypentafluoropropene [CF₂C(CF₃)-OCOC₆H₅] (BPFP) with tetrahydrofuran (THF), the reactions of bis(α-trifluoromethyl-β-difluorovinyl) terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with THF and of BPFP with 1,4-dioxane were investigated as model reactions to form 1 : 1 and 1:2 addition products of BFP with THF. This evidenced that THF is monofunctional, and dioxane is bifunctional since the 1:1 and 2:1 addition products of BPFP with dioxane were formed. The polyaddition reaction of BFP with dioxane turned out to produce a white powdery substance which was found to possess a mole ratio of BFP units to dioxane units in the polymers of 1:1. The highest molecular weight obtained was M _n = 9.9 × 10³.     

A Straightforward Route to Potent Phenolic Chain‐Breaking Antioxidants by Acid‐Promoted Transposition of 1,4‐Benzo[b]oxathiines to Dihydrobenzo[b]thiophenes

The transformation of simple phenols with limited antioxidant activity into potent chain‐breaking antioxidants was achieved by a three‐step protocol, consisting of the conversion of phenols into 1,4‐benzo[b]oxathiines followed by an unprecedented acid‐promoted transposition to o‐hydroxydihydrobenzo[b]thiophenes, or dihydrobenzo[de]thiochromenes, starting from phenols or naphthols, respectively. These derivatives, bearing a benzo‐fused heterocycle with a sulfide sulfur ortho to the phenolic OH, have a rate constant of reaction with alkylperoxyl radicals (k_inh) comparable to that of α‐tocopherol. A solid rationale for the transposition mechanism as well as for the structure‐antioxidant activity relationship is presented.     

1,4‐Dihydropyrrolo[3,2‐b]pyrrole and Its π‐Expanded Analogues

Various approaches to the synthesis of 1,4‐dihydropyrrolo[3,2‐b]pyrroles are summarized. Many two‐ and three‐step reaction sequences have been developed, and have allowed access to a broad variety of structures, including not only the parent 1,4‐dihydropyrrolo[3,2‐b]pyrroles, but also their π‐expanded analogues. The newest approaches are critically compared with older strategies. The reactivity of these compounds is also reviewed, with special emphasis on electrophilic aromatic substitution. The synthesis of indolo[3,2‐b]indole derivatives has been the subject of intense investigation. Overall, a few interesting and ingenious approaches toward these ladder‐type heteroacenes have been proposed, reaching total yields in the region of 30 %. Finally, the optical, electrochemical, and other physicochemical properties are presented in the broader perspective of heteropentalenes. The parent 1,4‐dihydro‐pyrrolo[3,2‐b]pyrroles constitute the most electron‐rich, simple, aromatic heterocycles, and their simple derivatives and π‐expanded analogues possess strong violet, blue, or green fluorescence both in solution and in the solid state.     

1,2-Versus 1,4-reduction of α,β-unsaturated carbonyl compounds in the gas phase

The regioselectivity involved in the gas-phase hydride reduction of α,β-unsaturated carbonyl compounds by pentacoordinate silicon hydride ions is investigated. The kinetics and product distributions of the reactions of acrolein, methyl vinyl ketone and cyclohex-2-enone with monoalkoxysiliconate ions of the general composition RSiH₃(OR′)^? were examined with the flowing afterglow–triple quadrupole technique. All three substrates react by hydride transfer and by formation of a siliconate adduct in which hydride reduction of the organic reactant has occurred. The structures of these adducts and the hydride transfer products were identified by various tandem mass spectrometric protocols, including analysis of competitive collision-induced dissociation (CID) reactions and comparisons of CID spectra obtained from reference ions with known structures. 1,4-Reduction forming an enolate ion product is found to be the dominant or exclusive process with all three substrates, i.e. acrolein (70 ± 5%), methyl vinyl ketone (72 ± 5%) and cyclohex-2-enone (100%). Comparisons are made between these gas-phase results and the regioselectivity reported for analogous condensed-phase reactions. The observed behavior is discussed in terms of the reaction thermochemistry.     

Me3SiCl and Et3SiI‐promoted one‐pot synthesis of 1,4‐dihydropyridine derivatives

An efficient synthesis of 1,4‐dihydropyridine derivatives has been achieved by the one‐pot cyclocondensation reaction of methyl 3‐aminocrotonate and a range of aldehydes in the presence of chlorotrimethylsilane as a promoter under solvent‐free conditions. The cyclocondenstion reaction requires a very short time and takes place in good to excellent yields. Furthermore iodotriethylsilane, generated in situ by the reaction of triethylsilane and methyl iodide in the presence of palladium chloride, has been investigated for the synthesis of 1,4‐dihydropyridine derivatives. This facile and efficient method affords high yields for the preparation of 1,4‐dihydropyridines at room temperature and short reaction times. Copyright © 2009 John Wiley & Sons, Ltd.     

Switching Regioselectivity of β‐Ketothioamides by Means of Iodine Catalysis: Synthesis of Thiazolylidenes and 1,4‐Dithiines

An efficient I₂‐catalyzed synthesis of thiazolylidenes and 1,4‐dithiines from β‐ketothioamides (KTAs) has been developed by only controlling the amount of I₂ that triggers different cascade reaction sequences by means of [3+2] or [3+3] cyclocondensation in a one‐step process. A possible mechanistic proposal for these transformations is presented.     

Diisopropyl tartrate (E)-γ-(dimethylphenylsilyl)allylboronate, a chiral allylic alcohol β-carbanion equivalent for the enantioselective synthesis of 2-butene-1,4-diols from aldehydes

An enantioselective synthesis of 4-substituted (E)-2-buten-1,4-diols is described. The method involves the reaction of aldehydes with the chiral PhMe₂Si- substituted allylboronate3 followed by epoxidation (dimethyl dioxirane) and acid catalyzed Petersen rearrangement of the intermediate epoxysilanols.     

Homo-1,4-addition to cyclo-octa-1,4-diene and cyclohepta-1,4-diene

Cyclo-octa-1,4-diene and cyclohepta-1,4-diene give the bicyclic derivatives IIa–b and IVa–b on reaction with Br₂-CCl₄ or I₂-AgClO₄-MeOH respectively. Cyclo-octa-1,4-diene also undergoes homo-1,4-addition in the Prevost reaction with I₂-AgOAc or I₂-AgOCOPh in benzene.     

Theoretical investigations of 1,4‐butanediol and 2‐butene‐1,4‐diol cyclodehydration using postprocessing visualization of quantum chemical calculation data

Cyclodehydration of 1,4‐butanediol and 2‐butene‐1,4‐diol to the corresponding cyclic ethers was studied using the AM1 semiempirical method. It was established that the cyclodehydration reaction of 1,4‐butenediol and 2‐butene‐1,4‐diol is effected by converting of semicyclic conformers in the presence of acidic and basic active centers. The calculation results indicate that a concerted mechanism is probably realized in the cyclodehydration of both diols, while the sequences of the predicted steps in the cyclodehydration reaction for 1,4‐butanediol and 2‐butene‐1,4‐diol are different. The calculated reaction heats for 1,4‐butanediol and 2‐butene‐1,4‐diol transformations are ?184.029 and ?308.746 kcal/mol, respectively. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Deamination of 3-(dialkylamino)-1,4-diarylhex-5-en-1-ynes during vacuum distillation

During vacuum distillation of 3-(dialkylamino) derivatives of 1,4-diphenyl- and 4-phenyl-1-(p-chlorophenyl) hex-5-en-1-ynes deamination occurs resulting in a high yield of p-diarylbenzenes. The amines transformation into terbenzenes is a domino-reaction: first step consists in the β-elimination of secondary amines with the generation of conjugated dienyne which via an electrocyclic reaction transforms into cyclic allene intermediate. The latter after 1,3- or 1,5-hydride shift quickly converts into the final reaction products.     

Synthesis of β‐Keto Sulfones by a Catalyst‐Free Reaction of Aryldiazonium Tetrafluoroborates,Sulfur Dioxide,and Silyl Enol Ethers

A green approach for the generation of β‐keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst‐ and additive‐free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO ⋅ (SO₂)₂ (DABCO=1,4‐diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction.