Montmorillonite K10 clay-catalyzed synthesis of homoallylic silyl ethers: an efficient and environmentally friendly Hosomi-Sakurai reaction

Aromatic aldehydes react with allyltrimethylsilane in the presence of activated Montmorillonite K10 clay to give homoallylic silyl ethers in good to excellent yields.     

Facile one-pot synthesis of aliphatic bridged diaryloxy compounds,cyclic and crown ethers under mild conditions

We report here the facile, room temperature, catalyst free, one pot synthesis of aliphatic bridged diaryloxy compounds, cyclic and crown ethers. Anhydrous potassium carbonate (K₂CO₃) as a mild base along with dimethyl sulfoxide generates the phenoxide ion which facilitates the nucleophilic substitution of bromoalkanes to yield the corresponding crown ethers.     

Synthesis of benzo-fused medium ring cyclic ethers via a Michael addition-ring closing metathesis strategy involving nitroaliphatic compounds

Nitroalkenes derived from O-protected salicylaldehyde undergo facile Michael-type addition of nucleophiles possessing unsaturated tether. Ring closing metathesis of the Michael adducts provides benzo-fused medium ring cyclic ethers possessing a nitroalkyl functionality.     

Access to chiral homoallylic vicinal diols from carbonyl allylation of aldehydes with allyl ethers via palladium-catalyzed allylic C-H borylation

Chiral homoallylic vicinal diols are found in many bioactive compounds and are among the most versatile functional groups in organic chemistry. Here, we describe an asymmetric carbonyl allylation of aldehydes with allyl ethers proceeding via allylic C-H borylation enabled by palladium and chiral phosphoric acid sequential catalysis, providing facile access to homoallylic vicinal anti-diols in high yields and with excellent stereoselectivity. This protocol enables the total synthesis of aigialomycin D to be finished within 7 steps.     

A distinct approach for the rapid synthesis of homoallylic amines starting directly from nitro compounds in water

Three-component reactions of nitroarenes, benzaldehydes, and allyltributylstannane using indium in dilute aqueous HCl at room temperature afford the corresponding homoallylic amines in high yields within 5-10 min. The conversion in one-pot synthesis involves the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and aldehydes, and (iii) allylation of imines.     

A convenient synthesis of substituted 3-bromotetrahydrofurans from homoallylic alcohols

Substituted 3-bromotetrahydrofurans were prepared from homoallylic alcohols via bromination and cyclization in methanol in the presence of potassium carbonate.     

Stereoselective synthesis of functionalized vinyl ethers from allyl bromides activated by triethylamine

An efficient coupling reaction of allyl bromides with various alcohols as nucleophiles activated by triethylamine, leading to functionalized vinyl ethers in good yields and with full stereoselectivity.     

Access to fused pyrroles via the reaction of spiro-dienyl ethers with amines involving a chemoselective skeletal rearrangement

Under metal-free conditions, the reaction of spiro-dienyl ethers, derived from furan derivatives, with aromatic amines provided fused pyrroles. The reaction proceeded through an interesting and chemoselective skeletal rearrangement and provided an alternative protocol for the construction of pyrrole rings from furan derivatives.     

Synthesis of thiaazapodands from 4′-nitrobenzothiacrown ethers

A series of thiaazapodands were synthesized from 4′-nitrobenzothiacrown ethers by nucleophilic regioselective opening of the macrocycle on heating with methylamine in up to 94% yield. Dedicated to Academician V. A. Tartakovsky on his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1479–1481, August, 2007.     

Low temperature syntheses of thioketals from enol ethers and carbonyl compounds

A dithioacetalisation procedure at low temperature using TMSOTf as the promoter is described. This method proved highly efficient for unprecedented transprotection of ketone enol ethers and was successfully applied to polyfunctional sensitive substrates.     

Gadolinium(III) chloride: a novel and an efficient reagent for the synthesis of homoallylic alcohols

Carbonyl compounds efficiently undergo nucleophilic addition reactions with allylstannanes in the presence of GdCl₃·6H₂O in acetonitrile under extremely mild reaction conditions to give the corresponding homoallylic alcohols in excellent yields and with high chemoselectivity.     

A simple approach to highly functionalized benzo[b]furans from phenols and aryl iodides via aryl propargyl ethers

A variety of mono- and disubstituted phenols are alkylated with propargyl bromide to give phenyl 2-propynyl ethers, which were further coupled with aryl iodides under Sonogashira reaction conditions to give 3-phenoxy-1-aryl-1-propyne derivatives. The latter compounds underwent an initial Claisen rearrangement followed by ring closure to give functionalized benzo[b]furans in moderate to good yields.     

Synthesis of functionalized polycyclic compounds via a novel aromatic oxy-Cope rearrangement

Polycyclic compounds have been prepared by aromatic dianionic oxy-Cope rearrangements involving the π bonds of two phenyl rings in a [3,3] sigmatropic rearrangement.     

Regio- and stereochemical aspects in the synthesis of homoallylic alcohols from benzoins and their iodocyclisation to 2,3-diphenyltetrahydrofurans

Indium mediated allylation, crotylation and cinnamylation of benzoins and its substituted derivatives in THF-H₂O (2/1) provide a range of homoallylic alcohols. In general, the benzoins undergo allylation and crotylation in a sluggish manner compared to those observed earlier in the case of α-hydroxy aldehydes and are significantly affected by the electronic features of both the benzoin and indium organometallic reagent. The reactions exhibit higher order of diastereoselectivities than those observed for α-hydroxy aldehydes. The cinnamylation though proceeds in a highly diastereoselective manner but is restricted to only benzoin and 4,4′-dichlorobenzoin. The homoallylic alcohols undergo I₂ mediated intramolecular diastereoselective cyclization to provide 2,3-diphenyltetrahydrofuran derivatives. The relative stereochemistries in tetrahydrofurans and homoallylic alcohols have been assigned by coupling constants, NOE experiments and in one case by X-ray crystallography.     

An efficient protocol for the preparation of MOM ethers and their deprotection using zirconium(IV) chloride

An efficient protocol for the preparation of MOM ethers from alcohols and formaldehyde dimethyl acetal (DMFA) using ZrCl₄ (10 mol %) at room temperature under solvent free conditions has been developed. Similarly, the same Lewis acid, ZrCl₄ (50 mol %), in isopropanol at reflux was utilised for the deprotection of MOM ethers.     

Decomposition of vinyl ethers by alkalide K, K(15-crown-5)2 via organopotassium intermediates

The structure of vinyl ethers determines the direction of the C-O bond cleavage by alkalide K⁻, K⁺(15-crown-5)₂1. Highly reactive organopotassium compounds are intermediate products formed in the system containing phenyl vinyl ether, butyl vinyl ether, ethylene glycol butyl vinyl ether or triethylene glycol methyl vinyl ether. Vinylpotassium and butylpotassium react with 15-crown-5. The oxacyclic ring of the latter is opened in this case. Organopotassium ethers possessing CH₂CH₂O units eliminate ethylene. It results in various potassium alkoxides. The reaction of 1 with butyl vinyl ether occurs very slow as compared to other vinyl ethers and most of other reagents used till now.     

Elimination of bis(trimethylsilyl)stannylene from tris(trimethylsilyl)stannylated zirconocene and hafnocene chlorides

Reactions of (Me₃Si)₃SnK with Cp₂MCl₂ (M = Zr, Hf) give the respective stannylated metallocene chlorides. These complexes display a tendency to eliminate bis(trimethylsilyl)-stannylene under Cp₂M(Cl)SiMe₃ formation.     

Synthesis of functionalized diaryl selenides by the first [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with organoselenium compounds

Functionalized diaryl selenides were prepared by the first [3+3] cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with organoselenium compounds (i.e., 2-(phenylselanyl)-3-silyloxy-3-en-1-ones).     

Access to functionalized steroid side chains via modified Julia olefination

Various functionalized steroidal side chains were conveniently accessed by a modified Julia olefination strategy using a common sulfone donor and an appropriate α-branched aldehyde acceptor. For the coupling of these hindered classes of reaction partners (and in contrast to typically observed trends), the benzothiazolyl(BT)-sulfone anion gave superior outcomes compared to the phenyltetrazolyl(PT)-sulfone anion.     

A mechanistic study of the Hiyama-Nozaki allylation: evidence for radical intermediates

In course of chromium(II) mediated additions of relatively complex allylic bromides to aldehydes (Hiyama-Nozaki allylation) radical intermediates have been observed. From these findings a new mechanism of the allylation is derived.