The Diels—Alder reaction in organometallic chemistry VI. Diels—Alder reactions of α-pyrone with group IV element-substituted acetylenes

The Diels—Alder reactions of α-pyrone with Me₃SiCCSiMe₃, Me₃SiCCSiMe₂H, Me₂HSiCCSiMe₂H, Me₃GeCCGeMe₃, Me₃SiCCGeMe₃, Me₃SiCCSnMe₃ and EtCCEt were examined. All except the first two acetylenes gave the expected 1,2-disubstituted benzene product, in line with results obtained previously with Me₃SnCCSnMe₃. The first two acetylenes, Me₃SiCCSiMe₃ and Me₃SiCCSiMe₂H, also yielded benzene products containing substantial amounts of the 1,3-disubstituted benzenes, as well as minor amounts of the 1,4-isomers. This formation of unexpected isomers during these reactions was shown to result from acid-catalyzed rearrangement of the initially formed 1,2-disubstituted products, 1,2-(Me₃Si)₂C₆H₄ and 1-Me₃Si-2-Me₂HSiC₆H₄. The acidic impurities arose from pyrolysis of the bromobenzene solvent used or were introduced as contaminants of the α-pyrone. Such isomerizations were inhibited by addition of small amounts of triethylamine. The fact that no rearrangement took place with the other acetylenes is due to the scavenging of acidic impurities which might cause isomerization by the starting acetylene and the benzene product via metal—carbon bond cleavage processes.     

(Z)-a-Selanyl Alkenyl Grignard Reagents as Convenient Precursors for Stereoselective Synthesis of Trisubstituted Alkenes

Many biologically active compounds occurring in nature possess the structural skeleton of trisubstituted alkenes1-3. Difunctional group reagents, which have two different functional groups linked to the olefinic carbon atoms, for example, Se-Zr, Se-B, Se-Sn play important roles in organic synthesis, especially in developing a lot of convenient methods for stereoselective synthesis of substituted alkenes4. Recently, Tingoli et al.5 reported that (Z)-a-selanylvinyl p-toluenesulfonates can u…     

Synthesis and unusual [2+2]-cycloaddition reactions of ethyl 4-chloro-2-oxobut-3-ynoate with unactivated alkenes

The highly activated acetylenes, ethyl 4-chloro-2-oxobut-3-ynoate and ethyl 4-bromo-2-oxobut-3-ynoate, were prepared from readily available bis(trimethylstannyl)acetylene in two steps with high overall yield. An unusual ability of the former to furnish [2+2]-cycloadducts with 1,1-disubstituted alkenes in the absence of irradiation and catalysts was discovered. The cycloaddition of ethyl 4-chloro-2-oxobut-3-ynoate to the 1,2-disubstituted alkenes was shown to be effectively catalyzed with stannic chloride.     

(Z)-α-Selanyl Alkenyl Grignard Reagents as Convenient Precursors for Stereoselective Synthesis of Trisubstituted Alkenes

(Z)-α-Selanyl alkenyl Grignard reagents 2 were prepared conveniently by treatment of (-bromovinylselenides 1 with magnesium filings in THF. Intermediates 2 were reacted with alkyl iodides in the presence of CuI or Pd(PPh3)4 to afford (Z)-1,2-disubstituted vinylselenides 3, which were cross-coupled with Grignard reagents in the presence of (PPh3)2NiCl2 to give trisubstituted alkenes 4 stereoselectively in good yields.     

Synthesis of 1,2-disubstituted acetylenes via copper-catalyzed Suzuki coupling of organoboronic acids with 1,1-dibromo-1-alkenes

An efficient synthesis of 1,2-disubstituted acetylenes has been described. Reactions of organoboronic acids with 1,1-dibromo-1-alkenes in the presence of a catalytic amount of CuI (10 mol %), 8-hydroxyquinoline (10 mol %), and using potassium phosphate as base in C₂H₅OH afforded the desired 1,2-disubstituted acetylenes in good to excellent yields. It is important to note that the formation of 1,3-diynes, which are derived from the homocoupling of 1,1-dibromo-1-alkenes, can be almost completely suppressed under these optimized conditions.     

聚苯乙烯负载的β-溴乙烯基硒化合物的合成及其在固相合成多取代烯烃中的应用

多取代烯烃的合成一直是有机合成的重要内容之一,在维生素、前列腺素和昆虫信息素等天然产物中都含有（Z）-或（E）-构型的多取代烯基结构单元,元素及金属有机化合物组成的1,2-双官能团化合物在立体选择性地合成多取代烯烃方面的应用研究一直是有机合成的热点。     

Stereoselective synthesis of (E)-α-aryltellurenylvinylsilanes via hydromagnesiation reaction of alkynylsilanes

(E)-α-Aryltellurenylvinylsilanes have been synthesized stereoselectively via the hydromagnesiation of alkynylsilanes, followed by the reaction with aryltellurenyl iodides. (E)-α-Aryltellurenylvinylsilanes can undergo the cross coupling reaction with Grignard reagents in the presence of Ni(PPh₃)₂Cl₂ catalyst to afford (Z)-1,2-disubstituted vinylsilanes in good yields.     

Synthesis of 1,4-disubstituted 1,2,3-triazoles based on cobalt bis(1,2-dicarbollide)

An approach to the synthesis of new 1,4-disubstituted 1,2,3-triazoles, in which one or both substituents contain the cobalt bis(1,2-dicarbollide) fragment, was suggested based on the 1,3-dipolar cycloaddition of azides to alkynes catalyzed by copper(I) compounds. The reaction of cobalt bis(1,2-dicarbollide) azido derivatives with different terminal acetylenes led to 1,2,3-triazoles with the [((CH₂)₂X(CH₂)₂O-C₂B₉H₁₀)Co(C₂B₉H₁₁)] (X = O or CH₂) substituent at position 1 and the organic substituent at position 4. The [3+2] cycloaddition reaction of cobalt bis(1,2-dicarbollide) alkynyl derivatives with methyl azidoacetate furnished isomeric 1,4-disubstituted 1,2,3-triazoles with the metallacarborane fragment at position 4. 1,2,3-Triazole with metallacarborane substituents at positions 1 and 4 containing 36 boron atoms was also synthesized.     

Highly efficient synthesis of 1,2-disubstituted acetylenes derivatives from the cross-coupling reactions of 1-bromoalkynes with organoalane reagents

A Highly efficient route for the synthesis of 1,2-disubstituted acetylene derivatives has been developed by palladium catalyzed cross-couplings of alkynyl halides with (hetero)aryl aluminium reagents under mild conditions. This has given corresponding cross-coupling products good to excellent isolated yields of up to 99%. The aryls bearing electron-donating or electron-withdrawing groups in either alkynylhalides or arylaluminum substrates gave cross-coupling products good yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 1,2-disubstituted acetylenes derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.     

Phenanthrene synthesis by iron-catalyzed [4+2] benzannulation between alkyne and biaryl or 2-alkenylphenyl Grignard reagent

The [4+2] benzannulation reaction of internal or terminal alkynes with 2-biaryl, 2-heteroarylphenyl, or 2-alkenylphenyl Grignard reagents in the presence of Fe(acac)(3), 4,4'-di-tert-butyl-2,2'-bipyridyl, and 1,2-dichloro-2-methylpropane takes place at room temperature in 1 h to give 9-substituted or 9,10-disubstituted phenanthrenes and congeners in moderate to excellent yields. The reaction tolerates sensitive functional groups such as bromide and olefin. When applied to a 1,3-diyne, the annulation reaction takes place on both acetylenic moieties to give a bisphenanthrene derivative.     

Nouvelle methode de synthese des γ-lactones et (5H)furannones-2-monosubstituees

3-monosubstituted γ-lactones and 5-mono- or 3,5-disubstituted 2-(5-H)-furanones have been prepared by the reaction of Grignard reagents with lactols.     

SYNTHESE POLYCYCLISCHER [C]-ANELLIERTER THIOPHENE

Abstract

A benzene ring substituted with two acyl groups in ortho-position was built from α-dicarbonyl compounds and dibenzyl ketone via Diels-Alder reaction of the intermediate cyclopentadienones with 1,2-diaroyl acetylenes and subsequent decarbonylation. The polycycles which were synthesized in this way formed interesting new [c]-annellated thiophenes on reaction with tetraphosphorus decasulfide (P₄S₁₀).     

Mono‐ and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis‐1,4‐([3]Cumulene)‐p‐carboquinoid System

An extended π‐system containing two [3]cumulene fragments separated by a p‐carboquinoid and stabilized by two capping N‐heterocyclic carbenes (NHCs) has been prepared. Mono‐ and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4‐bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis‐1,4‐([3]cumulene)‐p‐carboquinoid as a result of the π‐accepting properties of the capping NHCs.     

Diisopropyloxy(η-cyclopentene)titanium for the diastereoselective synthesis of various 1,2-disubstituted cyclopentanes

The reaction of 3 equiv of cyclopentylmagnesium chloride with 2 equiv of titanium(IV) isopropoxide at low temperature (−70 to −50 °C) leads to the formation of 1 equiv of diisopropyloxy(η²-cyclopentene)titanium containing low amounts of the starting Grignard reagent. The sequential addition of two electrophiles onto this titanium complex involved as an intermediate in Kulinkovich-type reactions delivers various 1,2-disubstituted cyclopentane rings with generally high diastereoselectivity. Mechanistic considerations and possible extensions of this method are discussed.     

Sonogashira cross-coupling of 3-bromo-1,2-diones: an access to 3-alkynyl-1,2-diones

A new general method for the synthesis of enols of cyclic 3-alkynyl-substituted 1,2-diketones is developed. Sonogashira cross-coupling of silyl enolates of cyclic 3-bromo-cyclopentane- and 3-bromo-cyclohexane-1,2-diones with variety of substituted acetylenes afforded enols of cyclic 3-alkynyl-1,2-diones with good yields (up to 93%) in a short reaction time. The starting 3-bromo-1,2-diones are easily obtainable by direct bromination of 1,2-diones with NBS.     

Cp2TiCl2-Catalyzed Grignard exchange reactions with acetylenes. A convenient method for preparation of E-alkenyl Grignard reagents

Disubstituted acetylenes react with isobutylmagnesium halide in the presence of a catalytic amount of Cp₂TiCl₂ in ether to afford E-alkenyl Grignard reagents selectively and in almost quantitative yields. The regiochemistry of this hydromagnesation reaction is high for alkylarylacetylenes and silylacetylenes giving E-ArC(MgBr)CHR from alkylarylacetylenes, E-ArC(MgBr)CH(SiMe₃) from arylsilylacetylenes, and ECHRC(MgBr)(SiMe₃) from alkylsilylacetylenes, respectively. Thanks to the high reactivity of the Grignard reagent, the present reaction offers a novel, selective and operationally simple route for preparation of trisubstituted olefins.     

Direct synthesis of 4,4-disubstituted N-silyl-1,4-dihydropyridines

An unprecedented method for the preparation of 4,4-disubstituted 1,4-dihydropyridines is presented. It is based on the trapping reaction of 4-substitued N-silylpyridinium ions. When performed with dialkylmagnesium reagents, such as iPr₂Mg, silyl protected 4,4-disubstituted 1,4-dihydropyridines were obtained in up to quantitative yields. High 1,4-selectivity was found for sterically demanding nucleophiles, whereas small nucleophiles (Me₂Mg) tend to yield 1,2-addition-products. Grignard, dialkylzinc and organocopper reagents were found to give either no addition products or less favorable results. Reduction of the obtained 1,4-dihydropyridine with NaCNBH₃ in the presence of HCl, followed by treatment with tert-butyl dicarbonate provided the corresponding N-Boc protected piperidines with high yields.     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Efficient synthesis of substituted thieno[3,2-e]indoles

Efficient cyclization reactions of 5-aminobenzothiophene derivatives with internal and terminal acetylenes, giving 7- and 8-substituted thieno[3,2-e]indoles, are described. The reaction of 4-iodo-5-(methylsulfonamido)benzothiophene with terminal alkynes gave 7-substituted thienoindoles using general Sonogashira reaction conditions. Reaction of 5-amino-4-iodobenzothiophene with internal acetylenes, using Larock's heterocyclization reaction conditions, gave 7,8-disubstituted thieno[3,2-e]indoles.