Rhenium-catalyzed coupling of propargyl alcohols and allyl silanes

A mild method for the regioselective coupling of propargyl alcohols and allylsilanes is described. The method employs an air- and moisture-tolerant rhenium-oxo complex ((dppm)ReOCl3) as a catalyst for the formation of sp3-carbon-sp3-carbon bonds without the need for prior activation of the propargyl alcohol as a halide or pseudohalide. The stability of the high oxidation state rhenium complex allows for simple reisolation and reuse of the catalyst. A broad range of functional groups is tolerated including aryl halides, olefins, esters, and acid-labile functional groups such as acetals. Furthermore, displacement of the alcohol occurs preferentially even in the presence of other electrophiles such as primary alkyl halides and conjugated esters. The use of enantiopure crotylsilanes as coupling partners allows for the asymmetric construction of two adjacent stereocenters. The potential of this reaction is demonstrated in an asymmetric synthesis of delta-lactone, di-O-methylcalopin.     

Reactions of tertiary propargyl alcohols with sodium halides under oxidative conditions

The study of the reactions of tertiary propargyl alcohols with sodium halides under oxidative conditions is presented. With sodium iodide, α-iodoenones were formed, however, with sodium bromide or chloride the α-haloenones were only formed in low yields under anhydrous conditions. Conversely, upon addition of water to the reaction mixtures, α,α-dibromoketones and α,α-dichloroketones were formed in good yields, but α,α-diiodoketones were not observed.     

Trifluoromethylation of enamines under acidic conditions

A method for the trifluoromethylation of enamines using Me₃SiCF₃ leading to α-CF₃-substituted amines is described. The reaction is promoted by hydrofluoric acid generated from KHF₂ and either trifluoroacetic or triflic acid, and involves protonation of the enamine followed by transfer of the CF₃-carbanion from the silicon reagent to the cationic electrophile.     

Regioselective arylation of unsaturated silanes under phase transfer catalysis conditions

Conclusions The regioselective arylation of unsaturated compounds was carried out under metal complex and phase transfer conditions by the action of aryl iodides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1180–1183, May, 1988.     

Intramolecular reactions of acyclic N-acyliminium ions I propargyl silanes as nucleophiles

Intramolecular reactions of acyclic N-acyliminium ions with propargyl silanes, induced by protic or Lewis acid, lead to α-allenic amides or carbamates, i.e. derivatives of 3-vinylidene-pyrrolidine, 3-vinylidene-piperidine or 1-amino-2- -vinylidenecyclopentane.     

Direct synthesis of B-allyl and B-allenyldiisopinocampheylborane reagents using allyl or propargyl halides and indium metal under Barbier-type conditions

We report the first one-pot process for the asymmetric addition of allyl, methallyl, and propargyl groups to aldehydes and ketones using B-chlorodiisopinocampheylborane ((d)DIP-Cl) and indium metal. Under Barbier-type conditions, indium metal was used to generate allyl- and allenylindium intermediates, and subsequent reaction with (d)DIP-Cl successfully promoted the transfer of these groups to boron forming the corresponding chiral borane reagents. The newly formed borane reagents were reacted with aldehydes and ketones to produce the corresponding alcohol products in high yields and up to excellent enantioselectivity (98% ee). This method produced excellent enantioenriched secondary homoallylic alcohols from the allylation and methallylation of benzaldehyde. Using this method, the methallylation and cinnamylation of ketones afforded the highest enantioselectivities, while the propargylation of both aldehydes and ketones provided low enantiomeric excesses. In addition, this procedure provided the first synthesis of B-allenyldiisopinocampheylborane, which was characterized by (1)H and (11)B NMR spectroscopy. This is the first example of the direct synthesis of allylboranes that contained substitutions from the corresponding allyl bromide and indium, thereby expanding the utility of the DIP-Cl reagent. Hence, a general and straightforward route to these chiral organoborane reagents in one-pot has been developed along with the asymmetric Barbier-type allylation and propargylation of aldehyde and ketone substrates using these chiral organoborane reagents in subsequent coupling reactions.     

Direct cross-coupling of aryl alkynyliodines with arylsulfinic acids leading to alkynyl sulfones under catalyst-free conditions

A facile and efficient one-pot method has been developed for the construction of alkynyl sulfones via direct cross-coupling reaction of aryl alkynyliodines and arylsulfinic acids. The present transformation could be accomplished under catalyst- and additive-free conditions, providing a series of alkynyl sulfones in moderate to good yields with favorable functional group tolerance.     

Mukaiyama reagent-promoted metal-free preparation of alkynyl sulfones and phosphonates under mild conditions

An efficient and mild route for the formation sulfur or phosphor-substituted alkynes was herein demonstrated. The Mukaiyama reagent-mediated transformation started from easily-accessible substrates without carbon-carbon triple bonds, and the reaction proceeded under mild conditions (room temperature) in a one-pot manner, requiring for no transition metal-catalysts. The practical protocol featured for good functional groups tolerance (up to 41 examples) and high efficiency (up to 91% yields) towards alkynyl sulfones and alkynyl phosphonates at low cost.     

Halogenation of propargyl ethers of heterylaldoximes and ketoximes under interphase catalysis conditions

The halogenation of propargyl ethers of heterylaldoximes and ketoximes in interphase catalytic systems CX₄ (X=Cl, Br)/solid KOH/18-crown-6 leads selectively to the formation of the corresponding O-(halopropargyl)oximes. Latvian Institute of Organic Synthesis, Riga LV-1006. e-mail: kira@osi.lanet.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1325–1328.     

Alkylation of hetaryl methyl ketones by propargyl bromide under phase-transfer catalysis conditions

The alkylation of aryl and hetaryl methyl ketones by propargyl bromide using the phase-transfer catalysis system KOH (s)/18-crown-6/benzene is studied. The corresponding C-trialkylated products are selectively obtained in 34–78% yields. Dedicated to Professor Henk van der Plas on his 70th birthday. Latvian Institute of Organic Synthesis, Riga LV-1006, Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 495–497, April, 1999.     

Stability of NF membranes under extreme acidic conditions

Two commercial nanofiltration (NF) membranes (FilmTec NF-45 and Desal-5 DK) and two new NF-1 membranes made by BPT (Bio Pure Technology) for the purpose of a European Union funded research project (RENOMEM) were tested under extreme acidic conditions. The polyethersulphone (PES) ultrafiltration (UF) supports used for casting the BPT-NF-1 membranes were also tested under similar conditions. The 006 and 015 UF supports were found to be stable in 5% nitric acid at 20 and 80 °C for 4 and 3 months, respectively. Both supports (006 and 015) showed a significant reduction in flux after immersion in sulphuric acid at both temperatures. The BPT-NF-1 membranes showed excellent resistance to 20% sulphuric acid for up to 4 months at 20 °C but were attacked by the nitric acid solution. The resistance of the two commercial membranes in 20% sulphuric acid at 20 °C was generally lower than that of the BPT-NF-1 membranes. The NF-45 membrane was slightly more stable in 5% nitric acid at 20 °C. Degradation of the membrane occurred only after 2 months while both the Desal-5 DK and BPT-NF-1 membranes degraded during the first month. At the higher temperature of 80 °C in 5% nitric acid all membranes degraded in the first month.The cause of membrane degradation was attributed to oxidation of the thin NF selective skin layer in nitric acid and to acid-catalysed hydrolysis of this layer in sulphuric acid. Knowing the cause of membrane degradation is a step forward in developing a better and more stable nanofiltration membrane.     

Comparative study on the reactivity of propargyl and alkynyl sulfides in palladium-catalyzed domino reactions

Three types of sulfides bearing a propargyl or an alkynyl moiety have been studied in cyclocarbopalladation/cross-coupling domino palladium-catalyzed sequences. The reactivity of different types of sulfured starting materials has been compared as well as the difference in behavior of these compounds depending on the type of cross coupling ending the domino sequence. It appeared that these cascades were constantly more efficient on the propargyl benzyl thioether. In addition, it has been demonstrated that domino sequences ending with Stille, Suzuki–Miyaura, or Mizoroki–Heck lead efficiently and selectively to the desired cyclized products. Notably, when the introduction of an alkyne is targeted at the end of the cascade, it appeared that the Sonogashira coupling leads every time to the desired cyclic product in the mixture with the product resulting from the direct coupling between the aryl moiety of the substrate and the alkyne used as partner. Finishing the domino sequence with a Stille coupling instead of a Sonogashira one allowed improving significantly the ratio of the mixture in favor of the desired cyclized compound.     

Hydrothermal synthesis of hollow silica spheres under acidic conditions

It is well-known that silica can be etched in alkaline media or in a unique hydrofluoric acid (HF) solution, which is widely used to prepare various kinds of hollow nanostructures (including silica hollow structures) via silica-templating methods. In our experiments, we found that sto?ber silica spheres could be etched in generic acidic media in a well-controlled way under hydrothermal conditions, forming well-defined hollow/rattle-type silica spheres. Furthermore, some salts such as NaCl and Na(2)SO(4) were found to be favorable for the formation of hollow/rattle-type silica spheres.     

Novel rearrangements of sesquiterpenoid panasinsane derivatives under acidic conditions

The sesquiterpenoid panasinsane derivatives 11 and 14-16 have been prepared from caryophyllene oxide (7). The novel rearrangement reactions of compounds 11 and 14 under TCNE-catalyzed solvolysis conditions and the reactions of compounds 15 and 16 under superacid conditions (HSO3F/Et2O, -63 degrees C) have been investigated. The ginsenol derivative 17 is obtained from compounds 11 and 14 under TCNE-catalyzed conditions. The rearrangement of compounds 15 and 16 under superacid conditions leads to the novel sesquiterpene derivatives (1S,4S,7S,10S,11S)-3,3,10,11-tetramethyltricyclo[5.3.1.0(4,10)]undecan-1,11-yl sulfate (19) and (1S,4S,5S,8S)-2,2,4,8-tetramethyl tricyclo[3.3.2.1(4,8)]undecan-11-one (20). The influence of the secondary hydroxyl group at C-5 of the panasinsane derivatives on the course of these rearrangements is discussed.     

Palladium-catalyzed monoselective C-H borylation of acetanilides under acidic conditions

A practical Pd-catalyzed reaction was developed to achieve C-H activation/C-B cross-coupling of acetanilides under acidic conditions. The new reaction shows a good functional group tolerance and an exclusive mono-selectivity. This C-H borylation method may provide a generally applicable route for the conversion of C-H moieties into many other types of bonds.     

Asymmetric synthesis of alpha-amino allyl,benzyl, and propargyl silanes by metalation and rearrangement

[reaction: see text] Metalation of a Boc-protected N-silylamine alpha to nitrogen results in migration of the silicon from nitrogen to carbon (reverse aza-Brook rearrangement), yielding an alpha-amino silane. The Boc group acts initially as a metalation-directing group and then to stabilize the nitrogen anion, providing a driving force for the rearrangement. In the presence of (-)-sparteine, the new chiral center is formed in >90% ee from allyl, benzyl, and propargylamines.     

Luminescent heteropolynuclear or multicomponent complexes with polypyridyl-functionalized alkynyl ligands

Polypyridyl-functionalized alkynes are a class of bifunctional ligands and very useful for the design of heteropolynuclear or multicomponent arrays as optoelectronic materials at the molecular level. This article focuses on reviewing the recent progress in design of luminescent heteropolynuclear or multicomponent complexes composed of photoactive discrete subunits using 2,2'-bipyridyl, 1,10-phenanthroline or 2,2':6',2'-terpyridyl functionalized alkynyl ligands with both acetylide and polypyridyl groups. The preparation, molecular fabrication, structural features, and spectroscopic and luminescent properties are summarized to elucidate the correlation of structure and photophysical properties as well as triplet energy transfer between two or more photoactive organometallic subunits.     

Enhanced enantiostability of BINOL dimethyl ether under moderate acidic conditions

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