Aromatic allylation via diazotization: metal-free C-C bond formation

A new method for the synthesis of allyl aromatic compounds not involving any metal-containing reagent or catalyst has been developed. Arylamines substituted with a large number of different substituents were converted via diazotizative deamination with tert-butyl nitrite in allyl bromide and acetonitrile to the corresponding allyl aromatic compounds. The allylation reaction was found to be suitable for larger scale synthesis due to short reaction times, a nonextractive workup, and robustness toward moisture, air, and type of solvent.     

Pd-catalyzed asymmetric allylic alkylation. A short route to the cyclopentyl core of viridenomycin

A palladium-catalyzed asymmetric allylic alkylation effects a dynamic kinetic asymmetric transformation of racemic isoprene monoepoxide and a surrogate for Nazarov's reagent in which a quaternary center is created with exellent ee. The resultant adduct allows easy access to a substrate for ring-closing metathesis to form a cyclopentenone and sets the stage for an 11-step synthesis of the cyclopentyl core of the antibiotic antitumor agent viridenomycin. [reaction: see text]     

A new route to acyclic nucleosides via palladium-mediated allylic alkylation and cross-metathesis

A method for the syntheses of E-unsaturated acyclic nucleosides via a combination of palladium-catalyzed allylic alkylation and ruthenium-based cross metathesis is described. This approach provides a concise, efficient and reliable route to new nucleoside analogues.     

A short route to the synthesis of pyrroloacridines via Ullmann-Goldberg condensation

A concise method for the preparation of pyrroloacridines was reported via CuI mediated Ullmann-Goldberg condensation of 5-amino-2-methylindoles and o-halobenzoic acid derivatives followed by cyclization with POCl₃.     

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.     

A new route to cyclopentenones via ruthenium-catalyzed carbonylative cyclization of allylic carbonates with alkenes

[RuCl2(CO)3]2/Et3N and (eta 3-C3H5)RuBr(CO)3/Et3N are highly effective catalyst systems for carbonylative cyclization of allylic carbonates with alkenes to give the corresponding cyclopentenones in high yields. For example, treatment of allyl methyl carbonate (1a) with 2-norbornene (2a) in the presence of a catalytic amount of [RuCl2(CO)3]2 (2.5 mol %) and Et3N (10 mol %) at 120 degrees C for 5 h under 3 atm of carbon monoxide gave the corresponding cyclopentenone, exo-4-methyltricyclo[5.2.1.0(2,6)]dec-4-en-3-one (3a), in 80% yield with high stereoselectivity (exo 100%).     

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.     

Facile route to 1-phosphoryl- and 1-sulfonyl-1,3-dienes via palladium-catalyzed elimination of allylic acetates

The palladium(II)-catalyzed chloroacetoxylation of 1,3-dienes is employed to prepare 1-chloro-4-acetoxy-2-alkenes which are then transformed into 1-phosphoryl- or 1-sulfonyl-4-acetoxy-2-alkenes respectively. Elimination of acetate is promoted by palladium(O)-catalysis or by sodium hydride, producing the useful 1-phosphory]- or 1-sulfonyl-1,3-dienes.     

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.     

Zeolite NaY-promoted cyclization of farnesal: a short route to nanaimoal

The sesquiterpene nanaimoal was synthesized in 21% overall yield and in a biomimetic manner. As a key step, the acid-catalyzed cyclization of farnesal under zeolite NaY confinement conditions was used. The intrazeolite cyclization of farnesal affords as major product a double-bond isomer of nanaimoal, via a novel diastereoselective tandem 1,5-diene cyclization/Prins-type reaction.     

Chemoenzymatic dynamic kinetic resolution of allylic alcohols: a highly enantioselective route to acyloin acetates

Dynamic kinetic resolution (DKR) of a series of sterically hindered allylic alcohols has been conducted with Candida antarctica lipase B (CALB) and ruthenium catalyst 1. The optically pure allylic acetates obtained were subjected to oxidative cleavage to give the corresponding acylated acyloins in high yields without loss of chiral information.     

Reductive alkylation of beta-alkoxy aziridines: new route to substituted allylic amines

[reaction: see text] A new route to substituted cyclic allylic amines via the reductive alkylation of beta-alkoxy aziridines using excess alkyllithium reagents is described.     

An efficient protocol of iridium-catalyzed allylic substitution reaction and its application to polymer synthesis: complementary regio- and stereoselective allylation polycondensation via Ir and Pd catalyses

An efficient protocol of the Ir-catalyzed allylic substitution reaction is reported using N,O-bis(trimethylsilyl)acetamide as a base in the presence of nBu4NF as a cocatalyst. The reaction completely proceeded under very mild conditions, and a branched allylated compound that is not easy to access via the Tsuji-Trost reaction can be synthesized. The reaction system is practical enough to be applicable for polymer syntheses. The Ir- and Pd-catalyzed allylation polycondensations generally show complementary regio- and stereoselectivities. The Ir-catalyzed reaction is versatile, and a mixed dual regioselectivity such as a branched-linear selectivity on each electrophile can also be achieved.     

A short and highly stereoselective route to polyhydroxy-perhydroazaazulenes via a C-(d-galacto-pentopyranos-5-yl)isoxazolidine

A short and efficient route to enantiomerically pure hexahydroxy- and pentahydroxy-perhydroazaazulenes, ring-homologues of castanospermine, starting from the sole isoxazolidine derivative obtained in the 1,3-dipolar cycloaddition of a d-galactose-derived nitrone and methyl acrylate, is established. The procedure allows both backbone and stereochemical modulation of the products by choice of the starting monosaccharide. Structural assignment was based on crystallographic analysis of the starting isoxazolidine and NMR techniques. The products were tested for inhibitory activity against several glycosidases.     

A short synthesis of (±)-tecomanine via a Pauson-Khand-based route

The N-carboethoxy precursor to (±)-tecomanine has been prepared in 11 steps from 2-methyl-1-buten-3-yne. The key step, Pauson-Khand cyclization of a methylated 5-aza-6-nonen-1-yne succeeds, but only in low yield, a consequence of the dialkyl substitution about the azaenyne framework. Nevertheless, the overall sequence to that point is one of the more efficient to be described.     

An efficient route for the allylation of arylaldehydes to give enantiopure homoallylic alcohols

An efficient asymmetric synthesis of homoallylic alcohols is described by the allylation of carbonyl compounds using organocatalysts as chiral directors in the presence of tin metal. The effect of chiral environment is also studied on the allylation reactions. This method allows us to obtain two different enantiomers of homoallylic alcohol in the presence of the corresponding chiral compound. The protocol is applied to various aldehydes to obtain high yields and excellent enantioselectivities for the corresponding homoallylic alcohols.     

Iminosugar thioglycosides as glycosyl donors: a route to disaccharides with an iminosugar moiety

The iminosugar thioglycosides are used as glycosyl donors in glycosidation reactions. Thereby, iminosugar glycosides and disaccharide analogues with an iminosugar moiety are prepared. The yields are high and the method is stereoselective.     

The Friedel-Crafts allylation of a prenyl group stabilized by a sulfone moiety: expeditious syntheses of ubiquinones and menaquinones

An efficient synthetic method for the protected p-hydroquinone compounds 4 containing the C5 trans allylic sulfone moiety has been developed by the direct Friedel-Crafts allylation of the protected dihydroquinone 2 with 4-chloro-2-methyl-1-phenylsulfonyl-2-butene (7a) or 4-hydroxy-2-methyl-1-phenylsulfonyl-2-butene (7b). Expeditious total syntheses of coenzyme Q-10 and vitamin K2(20) have been demonstrated from these valuable key compounds 4a and 4b.     

Highly efficient route to o-Allylbiaryls via palladium-catalyzed three-component coupling of benzynes, allylic halides, and aryl organometallic reagents

[reaction: see text] o-Allylbiaryl derivatives have been prepared in good to excellent yields by the palladium-catalyzed three-component reaction of allyl halides, benzynes, and aryl organometallic reagents.