Novel Mg-organic reagents in organic synthesis. Cp2TiCl2 catalyzed intermolecular cyclomagnesiation of cyclic and acyclic 1,2-dienes using Grignard reagents

High-yield (>80%) catalytic intermolecular cyclomagnesiation of cyclic and acyclic allenes with the aid of Grignard reagents has been realized in the presence of Cp₂TiCl₂. The synthesized unsaturated bi- and tricyclic organomagnesium compounds (OMC) have been successfully converted in situ into thiophenes, unsaturated ketones, cyclic and acyclic hydrocarbons with high regio- and stereoselectivity.     

Heterocyclic enamides — Derivatives of imidazolidine nitrosyl radicals: Reactions with nucleophilic and electrophilic reagents

The reactions of the heterocyclic enamides — 4-alkyliden-2,2,5,5-tetraalkyl-3-formylimidazolidin-1-oxyls — with organomagnesium and organolithium compounds takes place at two reaction centers — the N-formyl group and the C=C endocyclic carbon atom — to give three types of product: 3-imidazoline derivatives, substituted formyl derivatives, or acyclic nitroxyl radicals. Enamides with POCl₃ in DMF gives products of electrophilic substitution at the exocyclic methylene group with retention of the N-formyl.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 620–624, May, 1988.     

Synthesis and transformations of metallacycles 41. Cyclomagnesiation of O-containing 1,2-dienes with Grignard reagents in the presence of Cp2TiCl2

A Cp₂TiCl₂-catalyzed intermolecular homocyclomagnesiation of O-containing 1,2-dienes and cross-cyclomagnesiation of O-containing 1,2-dienes with aliphatic 1,2-dienes of cyclic and acyclic structure have been accomplished using Grignard reagents, which led to mono- and bicyclic organomagnesium compounds in 61–94% yields.     

Stéréochimie des réactions de réactifs de grignard au niveau de l'atome de silicium d'un cyclosilane asymétrique

The stereochemistry of coupling reactions of Grignard reagents and symetrical organomagnesium compounds with the silicon atom of 1,2,3,4-tetrahydro-2-(1-naphthyl)-2-silanaphthalene is studied. The results show that the electrophilic at the leaving group, by the metal atom is not a main factor for the retention of the configuration. It is possible to give a first explanaion of the stereochemical pathway of these reactions by considerig the “hard and soft” character of the attacking organometallic as well as polarisability of the leaving group.     

Nucleophilic addition to substituted 1H-4,5-dihydroimidazolium salts

1H-4,5-Dihydroimidazolium salts 1 react readily with nucleophilic reagents originating cyclic products which may be stable or become transformed into acyclic compounds maintaining the structural ethylenediamine unit. With methylmagnesium iodide compound 1e affords the expected imidazolidine, but in the case of substituted 1-aryl-3-methyl-2-phenyl salts 1b-d the N-aryl-N′-methylethylenediamines 3b-d and acetophenone ( 4 ) were isolated, the process representing the transfer of the C-2 unit to a nucleophilic carbon. With alkaline cyanides salts 1 react efficiently affording α,α-diaminonitriles 5 . In these compounds the cyano group may be readily substituted by nucleophiles (hydroxyl anion, species with nucleophilic carbon and reagents that act by hydride ion transfer), in a way similar to the salts but with better yields.     

Cyclomagnesation of Olefins with Ethylmagnesium Bromide in the Presence of Titanium Complexes

Cyclomagnesation of terminal and cyclic olefins and 1,2-dienes with RMgHlg and R₂Mg in the presence of dichloro(dicyclopentadienyl)titanium(IV) gives non-Grignard cyclic and acyclic organomagnesium compounds. The reaction direction depends on the structure of unsaturated initial compound. The most probable reaction mechanism is discussed.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 363–368.Original Russian Text Copyright © 2005 by Dzhemilev, D’yakonov, Khafizova, Ibragimov.     

Copper-catalyzed electrosynthesis of 1-acyl-2,2-diphenylcyclopropanes and their behaviour in acidic medium

The formation of 1-acyl-2,2-diphenylcyclopropanes is performed under mild electrochemical conditions. These cyclopropane derivatives, through acid-catalyzed ring-opening, lead to γ,γ-diphenyl-β,γ-unsaturated carbonyl compounds which evolve into either substituted naphthalenes, or β-benzhydryl-α,β-cycloalkenones depending on the acyclic or cyclic nature of the intermediate allyl ketone.     

Cycloaromatization of α-oxoketene dithioacetals with 2-picolyllithium: A facile quinolizinium cation annelation

α-Oxoketene dithioacetals derived from various cyclic and acyclic ketones are shown to be useful intermediates for the synthesis of substituted and fused quinolizinium derivatives by reaction with 2-picolyllithium followed by cyclization in the presence of borontrifluoride etherate.     

Stereochimie de l'action des organomagnesiens et des organolithiens sur les dimethyl-1,2 alcoxy-1 silacyclobutanes

The reaction of organomagnesium organolithium compounds (alkyl, aryl, allyl and benzyl derivatives) with 1,2-dimethyl-1-alkoxy-l-silacyclobutanes proceeds with retention of configuration at the silicon atom. Stereochemical results are discussed in terms of the S_N2Si mechanism. The proposed configurations are supported by ¹H and ¹³C NMR data.     

Asymmetric synthesis of highly substituted azapolycyclic compounds via 2-alkenyl sulfoximines: potential scaffolds for peptide mimetics

The application of metalated, enantiomerically pure acyclic and cyclic 2-alkenyl sulfoximines for the synthesis of highly substituted aza(poly)cyclic ring systems is described. The method relies on a one-pot combination of a reagent-controlled allyl transfer reaction to alpha- or beta-amino aldehydes, followed by a Michael-type cyclization of the intermediate vinyl sulfoximines generated in the first step. The sulfur-free target compounds are preferentially obtained by samarium iodide treatment of the sulfonimidoyl substituted heterocycles. In addition to this methodological work, initial results on the biological activity of selected examples are reported. Furthermore, a concept for the transformation of peptidic lead structures into non-peptide mimetics is described, and the relevance of the new approach to highly substituted azaheterocycles in this context is discussed.     

An efficient one-pot synthesis of spiro dihydrofuran oxindole and spiro 2-hydroxytetrahydrofuran oxindole derivatives via (3+2) oxidative cycloaddition mediated by CAN

Spiro dihydrofuran oxindole derivatives were prepared via a (3+2) oxidative cycloaddition of 1,3-dicarbonyl compounds to 3-(phenyl-2-oxoethylidene)-1-methyloxindole and 3-benzylidene-1-methyloxindole derivatives mediated by ceric ammonium nitrate. In the case of the reaction of 3-(phenyl-2-oxoethylidene)-1-methyloxindole derivatives with acyclic 1,3-dicarbonyl compounds, spiro 2-hydroxytetrahydrofuran oxindole derivatives were obtained.     

Hydrosilylation of m-TMI: New siloxane based aliphatic polyisocynates

Well-characterized polyfunctional aliphatic isocyanates were obtained in high purity and quantitative yield by the hydrosilylation of m-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) with cyclic and acyclic hydrogementhylsiloxance. The products were characterized by ¹H- and ¹³C-NMR, IR, and GPC, and all result exclusively from ß-addition to m-TMI. Polymers with SiH Groups are also effective hydrosilylating agents of m-TMI. The isocyanato siloxanes can be used as precursors for star and network polymers as well as other poly-functional reagents, and examples of reactions with methoxy polyethylene glycol and with amine-containing compounds are discussed.     

含2-氯-5-吡啶甲基的双氰基取代乙烯酮缩胺类化合物的合成及生物活性

新烟碱类杀虫剂由于具有高效、低毒、无交互抗性和内吸性等特点,成为杀虫剂领域新的研究热点［１］．本文以Ｎｉｔｅｎｐｙｒａｍ为母体,首次合成了２－氰基－３－（２－氯－５－吡啶甲氨基）－３－甲硫基丙烯腈（９）,并以其为中间体合成了１９个双氰基取代的含２－氯...     

Mo_2(OAc)_4试剂在邻二醇类结构绝对构型确定中的应用

环状及非环状邻二醇结构的绝对构型的确定是一个令人关注的研究领域.目前国外文献介绍了一种通过使用过渡金属试剂Mo2(OAc)4进行环状及非环状邻二醇结构绝对构型研究的方法,只需将该试剂与溶液中的被测化合物混合即可形成螯合物,无需制备和分离,且立刻可以进行圆二色谱测定,通过诱导产生的一定波长下的Cotton效应与被测化合物的手性中心的关系,可以方便地应用螺旋规则完成绝对构型的研究.将系统地介绍这一方法学,包括对方法学的研究思路、实验步骤、对影响因素的研究结果,以及一些应用的实例.     

Nucleophilic transformations of cyclic phosphate triesters

Reactions of cyclic phosphate triesters, such as 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, with Grignard reagents such as phenyl-, alkyl-, ethynyl-, and allyl-magnesium halides result in ring opening leading to the corresponding phosphonates, via nucleophilic attack of carbon on the phosphorus atom. Treatment of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide with sodium borohydride yields ethyl 2-hydroxyethyl phosphite. This reaction is exclusive for the five-membered cyclic system: under these conditions acyclic phosphate triesters, such as triethyl phosphate, are unreactive and the analogous six-membered ring system, 2-ethoxy-1,3,2-dioxaphosphorinane 2-oxide reacts only partially to give unidentified phosphate esters and traces of phosphonate products. Both compounds were inert to NaBH₄.     

Asymmetric synthesis of pyrrolo[2,1-a]isoquinoline derivatives by 1,3-dipolar cycloadditions of stabilized isoquinolinium N-ylides with sulfinyl dipolarophiles

Enantiomerically pure pyrrolo[2,1-a]isoquinoline derivatives are obtained by 1,3-dipolar reactions of isoquinolinium azomethine ylides with enantiopure 3-p-tolylsulfinylacrylonitriles, tert-butyl (2E)-4,4-diethoxy-2-p-tolylsulfinylbut-2-enoate, and 5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones. Reactions evolve through the anti conformation of the ylide with complete regioselectivity. The facial selectivity is completely controlled by the configuration of the sulfinyl sulfur for acyclic dipolarophiles, whereas it is high (dr 83/17 or 89/11) but controlled by the C-5 configuration for sulfinylfuranones. Complete endo selectivity is observed with cyclic dipolarophiles and substituted acrylonitriles, but it is low with butenoate. The sulfinyl group also exerts a positive influence on the dipolarophilic reactivity toward these ylides.     

Reactifs de Grignard vinyliques γ fonctionnels : III. Addition a quelques derives carbonyles

Δt^α,β-Butenolides can be obtained by carbonation of γ-functionally substituted vinylic Grignard reagents, prepared by addition of organomagnesium compounds to α-acetylenic or α-allenic alcohols. By addition to aldehydes and ketones, these vinylic Grignard reagents yield diols, which give unsaturated ethers by cyclization reactions.     

Catalytic enantioselective aza-Diels-alder reactions of imines--an approach to optically active nonproteinogenic alpha-amino acids

A catalytic enantioselective aza-Diels-Alder reaction of imines has been developed. The reaction of N-tosyl alpha-imino ester with different dienes including activated, non-activated, cyclic, and acyclic dienes has been investigated in the presence of various chiral Lewis acids. A series of phosphino-oxazoline ligands have been synthesized and evaluated for the reaction. It was found that the combination of phosphino-oxazoline ligands with copper(I) salts gives the best results for the activated dienes, while BINAP-copper(I) complexes are good catalysts for all the dienes studied. In the case of activated acyclic dienes the aza-Diels-Alder products can be obtained in higher than 80% isolated yield and 96% ee, while for the unactivated cyclic dienes the exo diastereomer is formed as the major product in up to 95 % ee. For an activated cyclic conjugated diene, 2-trimethylsilyloxy-1,3-cyclohexadiene, the reaction proceeds as a Mannich-type addition reaction giving optically active gamma-oxo alpha-amino acid derivatives in good yields and up to 96% ee. The reaction of an unactivated acyclic diene, 2,3-dimethyl-1,3-butadiene, with the N-tosyl alpha-imino ester gives both the aza-Diels-Alder and aza-ene products, in a ratio of 9:1 favoring the aza-Diels-Alder product. Furthermore, a series of different imines have been synthesized and investigated as possible substrates for the present catalytic enantioselective aza-Diels-Alder reaction in order to obtain mechanistic insight. All imines studied gave moderate to high ee. Particularly, the reaction of the N-phenyl and N-p-methoxyphenyl substituted glyoxylate imines with Danishefsky's diene proceeded well affording the corresponding aza-Diels-Alder product in high yield with up to 91% ee at room temperature. The present catalytic enantioselective reaction of imines provided an effective route to optically active nonproteinogenic alpha-amino acids. The products of the catalytic enantioselective aza-Diels-Alder reaction of the cyclic dienes can be used for the preparation of key compounds such as natural products and compounds of pharmaceutical interest. The absolute configurations of five products have been solved by X-ray structural analysis, and it is found that the absolute configuration of the aza-Diels-Alder adduct is dependent on the substituent on the imine nitrogen atom. It turned out that the N-tosyl glyoxylate imine and N-p-methoxyphenyl glyoxylate imine give the aza-Diels-Alder adduct with opposite absolute configuration using the same enantiomer of the catalyst. On the basis of the results the mechanistic aspects for the reactions are discussed.     

An alternative quinoline synthesis by via Friedländer reaction catalyzed by Yb(OTf)3

Quinolines have been synthesized in very good yields from 2-aminoarylketones and differently substituted carbonyl compounds in the presence of Yb(OTf)₃ as the catalyst. The method is applicable to both cyclic and acyclic carbonyl compounds with only slight differences in the experimental procedure.     

Aminophosphinidene derivatives

Abstract

Elimination and fragmentation reactions lead to carbene analogous iminophosphanes which undergo 2 + 1 addition as well as insertion reactions. Secondary aminophosphanes and amino substituted three-membered phosphorus rings are phosphinidene transfer reagents and therefore valuable building units for cyclic and acyclic compounds. Synthetic routes to amino substituted diphosphenes and their reaction behaviour are reported.