Samarium diiodide mediated 6-exo cyclisations of methylenecyclopropyl ketones

6-exo Cyclisations of methylenecyclopropyl ketones, mediated by samarium diiodide, have been investigated with a series of substrates. The efficiency of the cyclisations are highly dependent on the stereochemistry of the cyclisation precursor.     

二碘化钐作用下缺电子烯烃的还原偶联反应

室温下SmI2-HMPA-t-BuOH-THF体系能顺利地将丁烯二酸二酯还原偶联为1, 2, 3, 4-四烷氧基羰基丁烷, 同样条件下, 亚苄基氰乙酸乙酯,α-乙氧羰基肉桂酸乙酯, α-乙酰基肉桂酸乙酯和亚苄基丙二酸亚异丙酯等化合物也发生还原偶联反应得到相应的二聚体。     

Development of novel and efficient synthesis of group 14 element (Ge and Sn) catenates by use of samarium (II) diiodide

Group 14 element catenates such as di-, tri-, poly-germanes, and polystannanes are efficiently synthesized by use of the one-electron reducing agent SmI₂ under mild homogeneous conditions in good yields.     

Samarium diiodide promoted formation of 1,2-diketones and 1-acylamido-2-substituted benzimidazoles from N-acylbenzotriazoles

N-Acylbenzotriazoles, when treated with samarium diiodide in THF, undergo self-coupling reaction to afford 1,2-diketones in good to excellent yields; while when treated with samarium diiodide in CH₃CN, they undergo ring-opening reaction to afford 1-acylamido-2-alkyl (or aryl) benzimidazoles in reasonable to good yields. A plausible mechanism was suggested.     

Mercury(II) mediated cyclisation of R-1-(1′-hydroxyethyl)-2-(1″-propenyl)-3-alkoxy-4-methoxybenzenes to chiral isochromanes

A protocol has been established for the transformation of chiral ortho 1-hydroxyethyl propenyl benzenes under both anaerobic and oxidative mercury(II) mediated conditions to produce chiral isochromanes. Further transformations of the former products yielded chiral isochromanquinones, while the latter afforded the corresponding chiral 4-hydroxyisochromanquinones.     

Electroreductive intramolecular coupling of N-(oxoalkyl)phthalimides: complementary method to samarium(II) iodide reduction

The electroreductive intramolecular coupling of phthalimides with ketones in the presence of chlorotrimethylsilane gave five- and six-membered trans-cyclized products stereospecifically (>99%). Similar electroreductive intramolecular coupling of phthalimides with aldehydes afforded five-, six-, and seven-membered trans-cyclized products stereoselectively (75-93%). On the other hand, the reductive coupling of N-(oxoalkyl)phthalimides with samarium(II) iodide gave cis-cyclized products stereoselectively (88->99%).     

Samarium(II)-induced coupling of acid chlorides with allylic halides

Samarium(II)-induced coupling of acid chlorides with allylic halides gave diallylated tertiary alcohols. Monoallylated allylic ketones could not be obtained.     

Intramolecular hetero-Michael addition of beta-hydroxyenones for the preparation of highly substituted tetrahydropyranones

Structurally diverse beta-hydroxyenones are shown to undergo nonoxidative 6-endo-trig ring closure to form highly substituted tetrahydropyranones. Amberlyst-15, Al(ClO(4))(3) x 9 H(2)O and [Pd(MeCN)(4)](BF(4))(2) were found to be suitable catalysts for these intramolecular conjugate additions, preventing side reactions, such as dehydration or retroaldolisation. The use of [Pd(MeCN)(4)](BF(4))(2) is particularly effective, as this palladium-mediated reaction is under kinetic control and generates tri- and tetrasubstituted tetrahydropyranones with high levels of diastereocontrol. In the presence of the Lewis acid Al(ClO(4))(3) x 9 H(2)O, the reaction proceeded with a similar level of diastereocontrol; however, in contrast to [Pd(MeCN)(4)](BF(4))(2), this catalyst can promote enolisation. The palladium-mediated reaction was also found to be compatible with an enantioenriched beta-hydroxyenone substrate, giving no loss of enantiopurity upon ring closure. The most distinctive synthetic development to emerge from this new chemistry is the possibility to access tri- and tetrasubstituted 2,6-anti-tetrahydropyranones from anti-aldol precursors. These compounds are particularly difficult to access by using alternative methodologies. Two modes of activation were envisaged for the ring closure, involving metal coordination to either the C=C or C=O functional groups. Experimental results suggest that C=O coordination was the preferred mode of activation for reactions performed in the presence of Al(ClO(4))(3) x 9 H(2)O or [Pd(MeCN)(4)](BF(4))(2).     

Reactivity of diacetylplatinum(II) complexes: Oxidative addition of halogens and hydrogen halides

Diacetylplatinum(II) complexes [Pt(COMe)₂()] ( = bpy, 3a; 4,4′-t-Bu₂-bpy, 3b), obtained by the reaction of [Pt(COMe)₂X(H)()] with NaOH in CH₂Cl₂/H₂O, were found to undergo oxidative addition reactions with halogens (Br₂, I₂) yielding the platinum(IV) complexes (trans, OC-6-13)/(cis, OC-6-32) [Pt(COMe)₂X₂()] ( = bpy, X = Br, 4a/4b; I, 4c/4d;  = 4,4′-t-Bu₂-bpy, X = Br, 4e/4f; I, 4g/4h). The diastereoselectivity of the reactions proved to be strongly dependent on the solvent. The oxidative addition of (SCN)₂ resulted in the formation of (OC-6-13)-[Pt(COMe)₂(SCN)₂()] ( = bpy, 4i; 4,4′-t-Bu₂-bpy, 4j). In a reaction the reverse of their formation, the diacetylplatinum(II) complexes 3 underwent oxidative addition with anhydrous HX (X = Cl, Br, I), prepared in situ from Me₃SiX/H₂O, yielding diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)₂X(H)()] ( = bpy, X = Cl, 5a; Br, 5b; I, 5c;  = 4,4′-t-Bu₂-bpy, X = Cl, 5d; Br, 5e; I, 5f). Furthermore, diacetyldihaloplatinum complexes 4 were found to undergo reductive elimination reactions in boiling methanol yielding acetylplatinum(II) complexes [Pt(COMe)X()] ( = bpy, X = Br, 6b; I, 6c;  = 4,4′-t-Bu₂-bpy, X = Br, 6e; I, 6f). All complexes were characterized by microanalysis, IR and ¹H and ¹³C NMR spectroscopy. Additionally, the bis(thiocyanato) complex 4j was characterized by single-crystal X-ray diffraction analysis.     

Application of (S)- and (R)-methyl pyroglutamates as inexpensive, yet highly efficient chiral auxiliaries in the asymmetric Michael addition reactions

Methyl N-(E-enoyl)pyroglutamates, derived from inexpensive and readily available in both enantiomeric forms pyroglutamic acid were found to be an efficient Michael acceptors in the addition reactions with nucleophilic glycine equivalent allowing for an efficient practical asymmetric synthesis of β-substituted pyroglutamic acids and related compounds.     

The samarium(II)-mediated intermolecular couplings of ketones and β-alkoxyacrylates: a short asymmetric synthesis of an antifungal γ-butyrolactone

The samarium(II) iodide-mediated coupling of ketones with β-alkoxyacrylates gives β-hydroxy-γ-butyrolactones in moderate yield. The process has been applied to the asymmetric synthesis of an antifungal, γ-butyrolactone natural product.     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for Michael addition of mercaptans to α,β-unsaturated carbonyl compounds

Copper(II) tetrafluoroborate has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under solvent-free conditions and in H₂O at room temperature. The reactions are very fast and are completed in 2 min to 1 h affording high yields. The rate of thiol addition was dependent on the steric hindrance at the β-carbon of the α,β-unsaturated carbonyl substrate. In the case of chalcones, the reactions are best carried out in MeOH as solvent.     

Synthesis of dithiafulvene–quinone donor–acceptor systems: isolation of a Michael adduct

π‐Conjugated donor–acceptor systems based on dithiafulvene (DTF) donor units and various acceptor units have attracted attention for their linear and nonlinear optical properties. The reaction between p‐benzoquinone and a 1,3‐dithiole phosphonium salt, deprotonated by lithium hexamethyldisilazide (LiHMDS), gave a product mixture from which the Michael adduct [systematic name: dimethyl 2‐(3‐hydroxy‐6‐oxocyclohexa‐2,4‐dien‐1‐ylidene)‐2H‐1,3‐dithiole‐4,5‐dicarboxylate], C₁₃H₁₀O₆S₂, was isolated. It is likely that one of the unidentified products obtained previously by others from related reactions could be a similar Michael adduct.     

Oxidative cyclisation of chalcones with thallium(III)nitrate: Synthesis of (Z)-2-phenylmethylene-7-nitro-3(2H)-benzofuranones

Oxidation of 2-hydroxy-3-nitrochalcones with thallium(III) nitrate gives (Z)-2-phenylmethylene-7-nitrobenzofuran-3(2H)-one derivatives, rather than the more usual 1,2-diaryl-3,3-dimethoxypropan-1-ones or the corresponding isoflavones.

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Oxydative Cyclisierung von Chalconen mit Thallium(III)nitrat: Synthese von (Z)-2-Phenylmethylen-7-nitro-3(2H)-benzofuranonen (Kurze Mitteilung)

Zusammenfassung Die Oxidation von 2-Hydroxy-3-nitrochalconen mit Thallium(III)nitrat ergab (Z)-2-Phenylmethylen-7-nitro-3(2H)-benzofuranon-Derivate und nicht die üblichen 1,2-Diaryl-3,3-dimethoxypropan-1-one bzw. die entsprechenden Isoflavone.

     

Construction of a new asymmetric reaction site: asymmetric 1,4-addition of thiol using pentagonal bipyramidal Hf(salen) complex as catalyst

Pentagonal bipyramidal Hf(salen) complex 1 was found to serve as a catalyst for 1,4-addition reaction of thiol to N-(2-alkenoyl)-2-oxazolidinones.     

Spirolactone syntheses through a rhodium-catalyzed intramolecular C-H insertion reaction: model studies towards the synthesis of syringolides

Model studies towards the total synthesis of syringolides using a rhodium-catalyzed intramolecular C-H insertion reaction as the key step are described. A highly stereospecific synthesis of spirolactones is achieved employing this methodology.     

Scandium(III) triflate mediated intramolecular ring expansion of aziridines: a direct access to 4-aryltetrahydroisoquinolines

A novel, high yielding facile synthesis of 4-substituted tetrahydroisoquinolines has been developed by employing scandium(III) triflate mediated intramolecular ring expansion of aziridines. The meta-substituted electron-donating group on the benzene ring facilitates trapping of an in situ generated benzyl carbenium ion cation leading to the formation of tetrahydroisoquinolines.     

Calix[4]arene-dithiacrown ethers: synthesis and potentiometric membrane sensing of Hg

A series of calix[4]arene-dithiacrown-5 and -dithiacrown-6 compounds in cone and 1,3-alternate conformations has been synthesized. Responses of these ionophores to Hg²⁺ and competing metal ions were determined in solvent polymeric membrane electrodes. High potentiometric selectivity for Hg²⁺ over Na⁺ and a variety of transition and heavy metal ions was obtained.     

Selective nitrosation of guanazine: preparation of azidoaminotriazole and nitrosoguanazine anion-Cu(II) complexes

Guanazine (3,4,5-triamino-1,2,4-triazole) is selectively nitrosated on C-NH₂ to produce nitrosoguanazine (3-nitrosamino-4,5-diamino-1,2,4-triazole). The nitrosoguanazine is used to prepare 5-azido-3-amino-1,2,4-triazole and nitrosoguanazine anion-Cu(II) complexes.     

SmI2-mediated elimination reaction of Baylis-Hillman adducts controlled by temperature: a facile synthesis of trisubstituted alkenes and 1,5-hexadiene derivatives with E-stereoselectivity

Promoted by samarium diiodide, the Baylis-Hillman adducts undergo hydroxyl elimination to form trisubstituted alkenes with total (E)-stereoselectivity in good to excellent yields. The flexibility of this method also opens a new route to synthesize a class of 1,5-hexadiene derivatives by temperature tuning.