Stereoselective synthesis of allylic sulfones via the oxonia-Cope rearrangement of homoallylic alcohols containing a homoallylic sulfone moiety

The homoallylic alcohols 3 that can be prepared by the indium-mediated addition of haloallylic sulfones 1 to aldehydes 2 undergo the oxonia-Cope rearrangement with aldehydes 2 to give rise to the allylic sulfones 4 containing a conjugated diene moiety in a highly stereoselective manner. Electron-rich aldehydes preferentially participate in this oxonia-Cope rearrangement with the homoallylic alcohols 3. Excellent correlations of the stereochemistry (anti-3 to trans-allylic sulfone 4 and syn-3 to cis-allylic sulfone 4) have been observed in the oxonia-Cope rearrangement.     

Mechanistic studies of the allylic rearrangements of alpha-silyloxy allylic silanes to silyloxy vinylic silanes

Mechanistic evidence suggests that the Lewis acid-promoted allylic rearrangement of alpha-silyloxy allylic silanes proceeds along an ionic reaction pathway involving a contact ion pair. The driving force for this transformation is alleviation of steric congestion at the allylic position of the alpha-silyloxy allylic silane and stabilization of pi cc by hyperconjugation.     

Metal-catalyzed rearrangement of cyclopropenes to allenes

A novel transition-metal-catalyzed rearrangement of silylated cyclopropenes to the corresponding allenes is described. The presence of both the trimethylsilyl group on the cyclopropene and the platinum catalyst are crucial for this rearrangement.     

Synthesis of allylic and homoallylic alcohols from unsaturated cyclic ethers using a mild and selective C-O reduction approach

Unsaturated cyclic ethers can be mildly and selectively reduced with catalytic amounts of B(C(6)F(5))(3) in the presence of an alkylsilane. The allylic position is preferentially reduced with minimal or no scrambling of olefin geometry. For electronically equivalent substrates, steric factors guide the reducing agent to the least substituted site.     

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.     

One-step regiospecific synthesis of allylic silanes - extension to benzylsilanes

Allyltrichlorosilanes are prepared according to a one-step regiospecific process based on the reaction of allyl chlorides with SiCl₄ and NiCp₂/HMPA (catalyst), in the presence of industrial methylchlorodisilane fraction. ⁴Benzyltrihalosilanes are similarly obtained.     

Catalytic regiodivergent kinetic resolution of allylic epoxides: a new entry to allylic and homoallylic alcohols with high optical purity

A novel regiodivergent kinetic resolution of a series of allylic epoxides with alkylzinc reagents is described. Results demonstrate the potential of chiral copper-phosphoramidite catalysts for enantiomer differentiation of allylic epoxides, allowing a chiral catalyst-stereoregulated synthesis of cyclic allylic and homoallylic alcohols with high optical purities.     

n-π Interactions in homoallylic methyl ethers a photoelectron spectroscopic study

The He I photoelectron spectra of several monocyclic and bicyclic methoxy compounds have been interpreted in terms of inductive effects and n-π interactions between the π_cc molecular orbital and the oxygen lone pair orbital n_o. The n-π interactions appear to be small, and are mainly through bond.     

Palladium(0)-catalyzed rearrangement of allyl enol ethers to form chiral quaternary carbon centers via asymmetric allylic alkylation

Herein we report the first palladium(0)-catalyzed asymmetric allylic alkylation (AAA) of allyl enol ether via π-allylpalladium intermediate using Trost chiral diphosphine. This unprecedented reaction produced very rare α-aryl quaternary aldehydes with multi-functional groups. The main novelty in the chemistry demonstrates that enol ethers can be used as precursors for π-allylpalladium intermediates, an observation that is certainly rare and to the best of our knowledge, perhaps without prior precedent. Chiral ligand (R,R)-L3 was found to be optimal in this Pd-AAA reaction and provided good to excellent yield (80–95%) and enantioselectivity (70–90%) with a range of analogs.     

Claisen rearrangement of aliphatic allyl vinyl ethers in the presence of copper(II) bisoxazoline

The Claisen rearrangement of 1-methyl-2-isopropyoxycarbonyl-6-propyl allyl vinyl ether catalyzed by copper(II) bisoxazoline (Cu-box) has been investigated using density functional theory. Both the phenyl- and tert-butyl-substituted Cu-box systems have been studied. Three different reaction media (vacuum, CH2Cl2, CH3CN) have been considered. In vacuum, the phenyl Cu-box catalyzed reaction yields a (1R,6R) configured major product with a low selectivity. The solvent induces a higher selectivity and a reversal of the absolute configuration (1S,6S). However, the tert-butyl Cu-box catalyzed reaction yields (1R,6R) as the major product both in the gas phase and in the solvent with a good selectivity. Although chair-like TSs are lower in energy than boat-like TSs, the energy difference is small. This is because in the presence of the catalyst the distance between the allyl and vinyl parts of the substrate is relatively large, and thus the steric repulsion between them is smaller than would normally be expected for boat-like structures. The enantioselectivity of tert-butyl Cu-box originates from the steric interactions between the substrate and the catalyst, which are less important for the phenyl Cu-box where the enantioselectivity is determined by the solvent effects.     

On the PdCl2-catalyzed synthesis of allylic azides and allylic sulfonamides from homoallylic alcohols

According to experimental and literature data, the one-pot formation of allylic azides or sulfonamides from catalytic amounts of PdCl₂, homoallylic alcohols and TMSN₃ or TsNH₂ occurs through CC migration followed by regioselective nucleophilic addition on the Pd^II-activated CC bond and β-OH elimination.     

The synthesis of homoallylic amines utilizing a cuprate-based 1,2-metalate rearrangement.

Lithiation of the N-2,4,6-triisopropylbenzenesulfonyl-2-pyrroline (16) and treatment of the resulting cyclic vinyllithium reagent with R2CuCNLi2 produced an acyclic vinyl organometallic species that, when treated with an electrophile (H2O or RX), gave the homoallylic sulfonamides 18a-k in 37-93% yields and in > 95% diastereoselectivity. The deprotection of a representative homoallylic sulfonamide 18d was achieved in 83% yield by sonication in the presence of lithium wire and catalytic 4,4'-di-tert-butylbiphenyl (DBB). The efficacy of this general procedure for the production of homoallylic amine derivatives is demonstrated by the preparation of the diene amine 25, a key intermediate in the synthesis of a squalene synthetase inhibitor.     

From allylic alcohols to chiral tertiary homoallylic alcohol: palladium-catalyzed asymmetric allylation of isatins

A palladium-catalyzed asymmetric allylation of isatins with allylic alcohols as an allyl donor was developed by using chiral spiro phosphoramidite ligands. A variety of chiral tertiary homoallylic alcohols 3-allyl-3-hydroxy-2-oxindoles were prepared directly from allylic alcohols in one step with excellent yields and moderate enantioselectivities. This represents the first catalytic asymmetric allylation of ketones with allylic alcohol as the allylating agent.     

Addition reactions of ethoxycarbonylnitrene and ethoxycarbonylnitrenium ion to allylic ethers

Ethoxycarbonylnitrene (EtOCON) generated by α-elimination adds cleanly to allylic ethers giving substituted aziridines. Similar addition via nitrenium ion (EtOCONH⁺) gives derivatives of β-amino alcohols.     

Copper-mediated displacements of allylic THP ethers on a bisphosphonate template

The copper-mediated displacement of allylic THP ethers by Grignard reagents has been examined in a system that contains a geminal bisphosphonate ester. With Grignard reagents derived from several aromatic halides or benzyl bromide the displacement proceeds in attractive yields, but more mixed results were obtained from reactions with alkyl halides. In addition to its role as a nucleophile, the Grignard reagent also appears to deprotonate the bisphosphonate to generate an anionic intermediate. Formation of this anion appears to limit competitive nucleophilic attack at the phosphonate group and provides an intermediate that can be trapped by reaction with an electrophilic reagent such as methyl iodide to access a more substituted system.