A novel samarium(II)-mediated tandem spirocyclization onto an aromatic ring

We report a samarium(II)-mediated tandem spirocyclization reaction to provide dispiro[4.2.4.2]tetradecadiene and dispiro[4.2.5.2]pentadecadiene skeletons. The reaction was achieved by intramolecular addition of a ketyl radical onto an aromatic ring bearing an electrophilic moiety followed by reductive capture of the spirohexadienyl radical intermediate with SmI₂ in the presence of HMPA.     

The first samarium(II)-mediated aryl radical cyclisation onto an aromatic ring

Intramolecular arylation of aryl radicals was mediated by SmI(2)/HMPA in the presence of i-PrOH to give spirocycles and/or reduced cine-cyclised products, while the reaction in the absence of i-PrOH gave the rearomatised fused rings.     

Samarium(II)-mediated spirocyclization by intramolecular aryl radical addition onto an aromatic ring

Samarium(II)-mediated spirocyclization by intramolecular addition of aryl radicals onto an aromatic ring was achieved by the reaction of N-(2-iodophenyl)-N-alkylbenzamides with SmI2 in the presence of HMPA, yielding spirocyclic indolin-2-one derivatives. The ether congeners afford spirocyclic benzofuran derivatives in moderate yields by aryl radical addition onto a benzene ring without having an electron-withdrawing group. The reaction with other aryl groups such as naphthalene and indole rings is also described.     

Samarium(II)-promoted radical spirocyclization onto an aromatic ring

Samarium(II)-mediated spirocyclization onto an aromatic ring was achieved by the reaction of methyl 4-(4-oxoalkyl)benzoates with SmI(2) in the presence of i-PrOH and HMPA, yielding methyl 1-alkyl-1-hydroxyspiro[4.5]dec-6-ene-8-carboxylates in moderate to high yields. Utilizing this chemistry, spiro[3.5] and -[5.5] systems, and sterically congested spiro[4.5] systems, were easily synthesized. For the successful conversion, appropriate activation of the aromatic ring has proven to be extremely important: while an ester or amide functionality on the aromatic ring can promote the spirocyclization, a sulfonamide substituent causes ortho cyclization.     

The first stereoselective Pd-catalyzed addition of boronic acids onto aldehydes

The coupling reaction between 2-p-tolylsulfinyl benzaldehyde and substituted boronic acids catalyzed by Pd₂(dba)₃·CHCl₃ proceeds in a stereoselective manner, demonstrating the efficiency of the sulfinyl group as a chiral inductor. Enantiopure secondary diaryl alcohols become easily accessible by subsequent sulfoxide–lithium exchange.     

(Z)-alpha-haloacrylates: an exceptionally stereoselective preparation via Cr(II)-mediated olefination of aldehydes with trihaloacetates

(Z)-alpha-Fluoro-, (Z)-alpha-chloro-, and (Z)-alpha-bromoacrylates were obtained with unprecedented yield and stereocontrol (>99%) via addition of the corresponding commercial trihaloacetates to aldehydes at room temperature using stoichiometric Cr(II) salts or catalytic Cr(II) with a regeneration system. The intermediate 2,2-dihalo-3-hydroxy adducts could be isolated in good yields under conditions of limited reagent at 0 degrees C.     

Samarium(II)-mediated linker cleavage-cyclization in fluorous synthesis: reactions of samarium enolates

SmI2 has been used to cleave a sulfur linker and trigger cyclizations in strategies for the traceless fluorous synthesis of N-heterocycles. The studies give further insights into the reactivity of samarium enolates.     

A Samarium(II)-mediated, stereoselective cyclization for the synthesis of azaspirocycles

Unsaturated keto-lactams undergo sequential conjugate reduction-aldol cyclization on treatment with SmI 2 to give syn-spirocyclic pyrrolidinones and piperidinones containing vicinal, fully substituted stereocenters with complete diastereocontrol. The substituent on nitrogen and the lactam ring size have a marked impact on the efficiency of the spirocyclization.     

Formation of benzo-fused carbocycles by formal radical cyclization onto an aromatic ring

An indirect method for effecting radical carbocyclization onto aromatic rings is described. Cross-conjugated dienones such as 13, readily prepared by Birch reduction of aromatic tert-butyl esters, in situ alkylation, and oxidation (10 --> 11 --> 12 --> 13), undergo radical cyclization; the products (14) are aromatized by silylation, Saegusa oxidation, and treatment with BiCl3.H2O. A noteworthy feature of this route is that it provides opportunities to attach an additional substituent to the original aromatic ring.     

Switching between novel samarium(II)-mediated cyclizations by a simple change in alcohol cosolvent

Gamma,delta-unsaturated ketones undergo two very different stereoselective cyclization reactions mediated by samarium(II) iodide depending upon the alcohol cosolvent used in the reaction. Switching between an unprecedented aldol spirocyclization and a novel cyclobutanol-forming process can be achieved simply by changing the alcohol cosolvent from methanol to tert-butyl alcohol. [reaction: see text]     

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.     

The solid state electrochemistry of samarium (III) hexacyanoferrate (II)

A new electroactive polynuclear inorganic compound of a rare earth metal hexacyanoferrate, samarium hexacyanoferrate (SmHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction, UV–Vis spectrometry and X-ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of SmHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 180.5 mV (versus SCE) at a scan rate of 100 mV/s in 0.2-M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates up to as high as 1,000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of SmHCF and the transport behavior of K⁺, Na⁺ and Li⁺ counter-ions through the ion channel of SmHCF were studied by voltammetry.     

Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates

Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminated olefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.     

Cubic and doubly-fused cubic samarium clusters from Sm(II)-mediated reduction of organic azides and azobenzenes

A polynuclear samarium imido complex [(L)Sm(4)(μ(3)-NSiMe(3))(4)] (2) featuring a cubane-like cluster has been synthesized from the reaction of an organic azide and a samarium(II) complex [(L)SmI(2)Li(2)(THF)(Et(2)O)(2)] (1). In addition, this divalent samarium starting material (1) reacts with azobenzene to give the first example of a well-defined doubly-fused cubic imido-cluster [(L)Sm(6)(μ(3)-NPh)(4)(μ(4)-NPh)(2)I(2)(THF)(2)] (4) in addition to a major cubic complex [(L)Sm(4)(μ(3)-NPh)(4)] (3).     

Samarium(II)-mediated pinacol coupling in water: occurrence of unexpected disproportionation and action of low-valent samarium as an active species

[reaction: see text] Mechanistic studies of one-electron reduction in water using samarium were carried out. Unexpected disproportionation in water was observed via UV-vis spectroscopic analysis. This fact indicates that low-valent samarium species can exist in water. Furthermore, the SmCl(3)-Sm and SmCl(3)-Mg systems were found to act as good one-electron reducing agents in water.     

The remarkable effect of cosolvent on a samarium(II)-mediated 4-exo-trig cyclization: further synthetic studies on pestalotiopsin A

A samarium(II)-mediated 4-exo-trig cyclization in which a remote stereocenter serves to control the facial selectivity of the cyclization is described. The apparent coordination of a tert-butyldimethylsilyl ether to the samarium center appears to give rise to the selectivity. The remarkable effect of the cosolvent, 2,2,2-trifluoroethanol, on the cyclization of this substrate, is also discussed. A stereoselective synthesis of the general class of gamma,delta-unsaturated aldehyde cyclization substrate is reported, and the utility of the cyclization is demonstrated in an approach to the fully functionalized core of pestalotiopsin A.     

Ketyl-allene cyclizations promoted by samarium(II) iodide

[reaction: see text] Samarium(II) iodide has proven to be an effective reagent for intramolecular reductive coupling reactions. Previous investigations of intramolecular ketyl-olefin coupling reactions provided carbocycles in excellent yield and good diastereoselectivity. This method has been extended to ketyl cyclizations with allenes. Substrates leading to both carbocycles and heterocycles in a selective manner are explored.     

Remote functionalization: Cyclic alkoxylation onto aromatic ring via radical pathway

Oxidative cyclization of alcohols containing an aromatic ring with (diacetoxyiodo)benzene and iodine gave the corresponding cyclic ethers via alkoxy radicals in good yields. The present method is very useful for the direct preparation of flavonoid and vitamin E analogues from the alcohols.     

The first Ru(II)-catalysed asymmetric hydrogen transfer reduction of aromatic ketones in aqueous media

The first water-soluble asymmetric hydrogen-transfer ruthenium(II) catalyst system consisting of [Ru(p-cymene)Cl2]2, (S)-proline amide, and sodium formate, which gives high conversion rates with high ee values up to 95.3% and is reusable, has been developed.     

A stereoselective, Sm(II)-mediated approach to decorated cis-hydrindanes: synthetic studies on faurinone and pleuromutilin

The cis-hydrindane motif is found in a number of natural products that display important biological activity. A flexible, stereoselective approach to the framework has been developed that features highly diastereoselective, SmI(2)-mediated cyclisations. The strategy has been exploited in the first synthesis of the proposed structure of faurinone and an approach to the skeleton of the antibacterial natural product, pleuromutilin.