Tin mediated Barbier type allylation in ionic liquids

The Barbier type allylation of carbonyl compounds is a useful organic transformation as the resultant homoallylic alcohols are important building blocks for many biologically active molecules. Tin mediated Barbier allylation of different carbonyl compounds in room temperature ionic liquid, [BMIM][BF₄] afforded the corresponding homoallylic alcohols in good to excellent yields. The ionic liquid was successfully recycled and reused in allylation reactions.     

Aqueous Barbier allylation of aldehydes mediated by tin

The aqueous tin-mediated Barbier reaction affords good to excellent yields and moderate syn diastereoselectivity under basic and acidic conditions. The high yields and stereoselectivity observed in the case of o-substituted aldehydes suggest a cyclic organotin intermediate or transition state in K2HPO4 solution. A practical and efficient aqueous tin allylation of methoxy- and hydroxybenzaldehydes can be carried out in HCl solution in 15 minutes to afford the corresponding homoallylic alcohols in high yields. Aliphatic aldehydes give moderate to excellent yields with reaction times ranging from 30 to 60 minutes. Under these conditions, crotylation gives exclusively the gamma-product and the syn isomer is formed preferentially. For 2-methoxybenzaldehyde, an equilibration of the isomers to a syn/anti ratio of 1:1 can be observed after several hours. Control experiments with radical sources or scavengers give no support for radical intermediates. NMR studies suggest a mechanism involving an organotin intermediate. The major organotin species formed depends on the reaction medium and the reaction time. The use of acidic solution reduces the reaction times, due to the acceleration of the formation of the allyltin(IV) species.     

Rapid access to homoallylic alcohols via Pd(OAc)2 catalyzed Barbier type allylation in presence of DMAP

DMAP was found to accelerate significantly the rate of Pd(OAc)₂ catalyzed Barbier type allylation of carbonyl compounds by allylbromide using SnCl₂·2H₂O as reducing agent. Both aldehyde as well as ketones produced excellent yields within a short reaction time in the presence of 3 mol % of Pd(OAc)₂ and 12 mol % of DMAP at room temperature. Aldehydes could be allylated within 5–10 min whereas, in case of ketones, the reaction completes in 45–120 min.     

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.     

Metallic bismuth mediated allylation of aldehydes to homoallylic alcohols

In the presence of metallic bismuth, allyl halides were found to react with aldehydes under mild conditions to give the corresponding homoallylic alcohols in good yields.     

Highly efficient three-component synthesis of protected homoallylic amines by bismuth triflate-catalyzed allylation of aldimines

Bismuth triflate catalyzes the allylation of a variety of in situ generated protected aldimines using aldehydes, primary carbamates, and allyltrimethylsilane in a three-component reaction. The reaction proceeds rapidly and affords the corresponding protected homoallylic amine in good yield (up to 86%). Scope and limitations of the aldehyde and carbamate components are reported.     

Highly efficient synthesis of homoallylic alcohols and amines via allylation of aldehydes and imines catalyzed by ZrOCl2·8H2O in water

The allylation of aldehydes and imines has efficiently been carried out by treatment with allyltributylstannane in the presence of a catalytic amount of ZrOCl₂·8H₂O in water to form the corresponding homoallylic alcohols and amines, respectively, in high yields.     

Mild and efficient barbier allylation reaction mediated by magnesium powder under solvent-free conditions

A novel and highly efficient synthesis of homoallylic alcohols is achieved by the allylation of carbonyl compounds using magnesium powder as mediator under solvent-free conditions. A series of aldehydes and ketones are converted to the corresponding homoallylic alcohols, the yields of the reaction is considerably high (85-98%). The procedure is environment benign, operationally simple and easy to scale up at room temperature.     

Facile synthesis of γ-alkenylbutenolides from Baylis-Hillman adducts: consecutive in-mediated Barbier allylation, PCC oxidation, isomerization, and Zn-mediated Barbier allylation

Alkenylbutenolides were synthesized regioselectively in good to moderate yields from Baylis-Hillman adducts via a consecutive indium-mediated Barbier type reaction between Baylis-Hillman bromide and aldehyde, PCC oxidation of the homoallylic alcohol, double bond isomerization, and zinc-mediated Barbier type alkenylation protocol.     

Asymmetric allylation. An effective strategy for the convergent synthesis of highly functionalized homoallylic alcohols

A survey of stereoselective syntheses of highly-functionalized homoallylic alcohols is described via asymmetric allylation. Initial transmetalation from an allylic stannane to a C-2 symmetric chiral borane controller is followed by low temperature addition to aldehydes efficiently effecting convergent strategies to complex targets.     

Additive effects in palladium-indium mediated Barbier type allylations

The effect of adding 1 equiv. of an amine or 0.2 equiv. of CuI to a Pd/In bimetallic cascade reaction is described. In the class 1 cascade reaction of aldehydes, aryl iodides and allene, generating homoallylic alcohols, the reaction time is reduced from 16 to 2 h and is accompanied by an impressive increase in yield.     

A practical procedure of low valent tin mediated Barbier allylation of aldehydes in wet solvent

Use of aluminium as the reducing metal in spontaneous bimetal redox reaction has been elegantly exploited for allylation/crotylation of aldehydes in wet solvent. Here, low valent tin was prepared in situ by reduction of SnCl₂·2H₂O with aluminium in THF/water. The resulting low valent tin acted as an efficient mediator for allylation and crotylation of aldehydes (3a–q) producing the corresponding homoallylic alcohols. The efficacy of this procedure was due to its operational simplicity, practical viability, inexpensiveness, good yields of the products and short reaction time.     

Highly efficient synthesis of amides via Ritter chemistry with ionic liquids

The utility of Brønsted-acidic imidazolium ionic liquid [BMIM(SO₃H)][OTf] as catalyst for the high yield synthesis of a wide variety of amides under mild conditions via the Ritter reaction of alcohols with nitriles has been demonstrated. As alternative methods for the carbocation generation step, NOPF₆ immobilized in [BMIM][PF₆] ionic liquid was used in the Ritter reaction of bromides with nitriles and for the synthesis of adamantyl amides from adamantane and nitriles.     

Gallium metal mediated allylation of carbonyl compounds and imines under solvent-free conditions

Gallium metal is effective in mediating the allylation of various carbonyl compounds and imines under solvent-free conditions, with the application of sonic energy, affording the corresponding homoallylic alcohols and amines. The imines themselves were also prepared under solventless conditions in high yield, thereby establishing a two-step solvent-free synthesis of homoallylic amines. In comparison, indium metal produced a mixture of the desired homoallylic secondary amine and the bis-allylated species via an iminium ion intermediate.     

Remarkable salt effect on In-mediated allylation of N-tert-butanesulfinyl imines in aqueous media: highly practical asymmetric synthesis of chiral homoallylic amines and isoindolinones

A highly practical and efficient asymmetric synthesis of chiral homoallylic amines by In-mediated allylation of chiral N-tert-butanesulfinyl imines in aqueous media at room temperature was developed. With 2-formylbenzoate imine substrates, the method allows the highly enantioselective achievement of a variety of pharmacologically important 3-allyl isoindolinone compounds.     

Mild and efficient one-pot synthesis of chiral β-chalcogen amides via 2-oxazoline ring-opening reaction mediated by indium metal

A simple and efficient procedure for the synthesis of β-seleno and β-thio amides via the ring-opening reaction of chiral 2-oxazolines in the presence of indium metal has been developed. Features of this method include the following: (i) easily and accessible starting materials; (ii) indium metal is more stable and less expensive then its respective salts; (iii) useful to excellent yields of β-chalcogen amides derivatives.     

An efficient organocatalyzed multicomponent synthesis of diarylmethanes via Mannich type Friedel-Crafts reaction

We have developed an efficient organocatalyzed, multicomponent synthesis of diarylmethane derivatives from tertiary aromatic amines, formaldehyde and 2-naphthols via Mannich type Friedel-Crafts reaction. Several organocatalysts such as (−)-chinchonidine, l-proline, l-thiaproline, and l-pipecolonic acid have been screened for the reaction but the best results were obtained with l-proline. In this Mannich type Friedel-Crafts alkylation, tertiary aromatic amines react with formaldehyde-proline adduct to generate 1-(4-(dimethylamino)benzyl)pyrrolidinium-2-carboxylate intermediate, which undergoes nucleophilic addition to give substituted diarylmethanes in excellent yields.     

A new method for the synthesis of amides from imines

An efficient and straightforward method for the synthesis of amides by the reaction of imines and anhydrides in the presence of Et₃SiH/Zn is reported. Mild reaction conditions, good yields of products, short reaction times, and operational simplicity are advantages of this procedure.     

An expedient synthesis of poly-substituted pyrroles from γ-ketonitriles via indium-mediated Barbier reaction strategy

We developed an efficient synthetic strategy of poly-substituted pyrroles via an indium-mediated Barbier type allylation from γ-ketonitriles. Initial attack of allylindium species occurred at the nitrile group selectively to form the enamine intermediate, which reacted with the ketone group intramolecularly to furnish the pyrroles.