Indium-mediated asymmetric Barbier-type allylation of aldimines in alcoholic solvents: synthesis of optically active homoallylic amines

[reaction: see text] Chiral aldimines derived from phenylglycinol were diastereoselectively allylated with indium powder/allyl bromide in alcoholic solvents. Both aliphatic and aromatic aldimines provided good yield of the desired products with high diastereoselectivity. A racemization-free protocol for removal of the phenylglycinol auxiliary was also developed. The stereochemical assignment of the homoallylic amine was made by NMR spectroscopy and a transition state model was proposed to explain the selectivity.     

Enantioselective imidazole-directed allylation of aldimines and ketimines

A new chiral allylchlorosilane has been developed that allows the highly enantioselective allylation and crotylation of a range of 2-imidazolylaldimines and ketimines. The method may be exploited for the protecting group-free synthesis of a diverse array of imidazole-bearing chiral carbinamines and, when coupled with ring-closing metathesis reactions, allows the one-pot synthesis of unusual heterocyclic motifs with potential relevance in medicinal chemistry.     

Phenol-directed enantioselective allylation of aldimines and ketimines

[Structure: see text] Phenols are effective directing and activating groups for our allylchlorosilane reagents, allowing the highly enantioselective allylation of a range of 2-aminophenol-derived aldimines. When the phenol is incorporated into the substrate ketimines may be allylated highly enantioselectively, leading to the experimentally simple synthesis of a range of tertiary carbinamine structures.     

A facile synthesis of N-sulfonyl and N-sulfinyl aldimines under Barbier-type conditions

A convenient synthesis of N-sulfonyl- and N-sulfinylimines by the condensation of aldehydes with sulfonyl or sulfinyl amides in the presence of benzyl bromide and zinc dust at room temperature under the Barbier-type conditions is reported. The procedure is lauded by its simplicity and adaptability to aromatic, alpha,beta-unsaturated, and aliphatic aldehydes.     

Stereoselective Mannich-type reaction of chlorotitanium α-phenylseleno esters enolates with aromatic aldimines

The stereoselective Mannich-type reaction of α-phenylseleno chlorotitanium enolates with aromatic aldimines is described. The corresponding α-phenylseleno-β-amino esters were obtained in good yields and with moderate to good diastereoselectivity. A rationale for the predominant syn selectivity based on a chelated cyclic transition state is suggested. The obtained compounds are useful synthetic tools and direct precursors of new α-phenylseleno-β-lactams.     

Pd/Sn promoted Barbier-type allylation and crotylation of sulfonimines

A one-pot Barbier protocol is described for the facile formation of homoallyl sulfonamides from sulfonimines and allyl or crotyl bromide in the presence of SnCl₂, and catalytic Pd₂(dba)₃·CHCl₃ at room temperature.     

Stereoselective allylation of chiral monoperoxyacetals

Neighboring iodo-, alkoxy-, acetoxy- and silyl groups impart useful levels of diastereoselection in the Lewis acid-mediated allylation of monoperoxyacetals. Although monoperoxyacetals are found to be considerably less reactive than corresponding nonperoxidic acetals, similar stereochemical trends are observed in the two series.     

Stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes by using trifluoromethanesulfonic acid

Novel stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes in the presence of trifluoromethanesulfonic acid has been carried out to give the corresponding products, which are not obtained by general Lewis acid-promoted methods, with 70-92% de in 62-74% yield. No cycloadducts were detected in the crude product by ¹H NMR.     

First enantioselective organocatalytic allylation of simple aldimines with allyltrichlorosilane

A new organocatalytic system, novel chiral bisformamide and in situ generated L-proline-derived allylsilane reagent , which converts different aldimines to homoallylic amines in good to high yields (up to 95%) and good enantioselectivities (up to 85% ee) has been described.     

Stereoselective synthesis of C-ketosides by sequential intramolecular hydrogen atom transfer-intermolecular allylation reaction

A tandem 1,5 or 1,6 hydrogen atom transfer (HAT)-radical allylation using carbohydrate models is described. The HAT reaction generated a C-glycos-1-yl radical intermediate, which added to allyltri-n-butyltin with high diastereoselectivity, to give C-ketosides with the quaternary carbon carrying two differently functionalized tethers.     

Barbier-type allylation of iminium ions generated in situ in aqueous medium

Iminium ions, generated in aqueous solution from secondary amines and formaldehyde, undergo a Barbier-type allylation mediated by tin, aluminum and zinc. The reaction is catalyzed by copper and produces tertiary homoallylamines in up to 85% yield.     

Formation of quaternary carbon center with a trifluoromethyl group using a Pd-catalyzed allylation reaction

Synthesis of compounds with quaternary carbons is one of the most attractive reactions in the synthetic chemistry. However, there are only a few reports on synthesis of the compounds with a fluoroalkyl group at a quaternary carbon center. Recently, we reported the synthesis of alpha-trifluoromethylated ketones by the reaction of alpha,beta-unsaturated ketones with CF(3)-I using a Rh catalyst. When the alpha-trifluoromethylated ketones and allyl carbonates were treated with a Pd catalyst, the allylation reaction proceeded smoothly at the trifluoromethylated carbon to give the desired compounds with a trifluoromethylated quaternary carbon center in good to excellent yields.     

Solvent-free allylation and benzylation of aldimines mediated by zinc powder

A rapid and efficient procedure for allylation and benzylation of aldimines mediated by zinc powder under solvent-free conditions is described. The procedure is operationally simple, higher regioselective, and gives good to excellent yields.     

Barbier-type reaction with trialkylstibine 1

In the presence of trialkylstibine, various aldehydes react readily with allyl halides to form homoallylic alcohols in excellent yield.     

Stereoselective allylation for preparation of L-hexose derivatives

The reaction of allyltrimethylsilane with α,β-dialkoxyaldehydes is catalyzed by magnesium bromide, and provides for a highly stereoselective allylation which is predicted by α-chelation of the Lewis acid. The observed stereocontrol is opposite to that generally obtained from a variety of common allylation reagents.     

Stereoselective allylation of azirines with allylindium reagents

Allylindium reagents allylated azirines to give allylaziridines in good yields. The delivery of the allyl group was well regulated by the substituents at the C³-carbon of azirines. The cis-allylation with respect to the substituent was realized with azirines bearing a hydroxylmethyl or an acetoxymethyl group due to the chelation with allylindium reagents, whereas the trans-allylation was achieved with azirines substituted by a methyl, phenyl, or ester group owing to the steric repulsion.     

Asymmetric indium-mediated Barbier-type allylation reactions with ketones to form homoallylic alcohol products

We report a general method for the enantioselective allylation of both aromatic and aliphatic ketones under indium-mediated Barbier-type conditions. Using 2 equiv of a commercially available amino alcohol, either (1S,2R)-(+)-2-amino-1,2-diphenylethanol ((+)-1) or (1R,2S)-(−)-2-amino-1,2-diphenylethanol ((−)-1) as the chiral auxiliary, good yields and enantioselectivities were achieved. To our knowledge, the enantioselectivities reported herein are the highest obtained for the indium-mediated allylations of ketones, specifically the homoallylic alcohol product obtained from the addition to α,α,α-trifluoroacetophenone provided 80% enantiomeric excess.     

Noticeable facilitation of the bismuth-mediated Barbier-type allylation of aromatic carbonyl compounds under solvent-free conditions

When milled together with bismuth shot in the presence of allyl halide, aromatic aldehydes readily underwent a Barbier-type allylation to afford the corresponding homoallyl alcohols in good yield. In contrast to the failure in solution reaction, aromatic ketones also underwent allylic carbonyl addition under solvent-free conditions to give the expected tertiary homoallyl alcohols in moderate to good yield.     

Stereoselective gamma-lactam synthesis via palladium-catalysed intramolecular allylation

A novel route to the synthesis of 3-(tolylsulfonyl)-4,5-cis-disubstituted gamma-lactams using a diastereoselective palladium-catalysed intramolecular allylation of amino acid-derived allylic carbonates has been developed.