Iron(III) p-toluenesulfonate catalyzed synthesis of homoallyl ethers from acetals and aldehydes

Iron(III) p-toluenesulfonate, Fe(OTs)₃·6H₂O, is an inexpensive, versatile and commercially available catalyst for the allylation of acetals using allyltrimethylsilane to yield homoallyl ethers in moderate to good yields. The one-pot conversion of aldehydes to homoallyl ethers using alkoxysilanes has also been accomplished using Fe(OTs)₃·6H₂O as a catalyst. The use of mild reaction conditions and a relatively non-corrosive catalyst make this method an attractive option for the synthesis of a range of homoallyl ethers.     

An Efficient Prins Cyclization for Stereoselective Synthesis of Tetrahydropyran from Imines and Homoallyl Alcohols

An unprecedented protocol has been developed for the efficient synthesis of substituted tetrahydropyrans via a bismuth‐promoted Prins cyclization of imines with homoallyl alcohols. In the presence of 40 mol% BiCl₃, a wide variety of imines react smoothly with homoallyl alcohols at room temperature to give the corresponding 4‐chlorotetrahydropyran derivatives in good to excellent yields.     

Highly efficient iron‐catalyzed allylation of aromatic aldehydes with allyltriethoxysilane: one‐pot and practical synthesis of homoallyl ethers

FeCl₃ was found to be an active catalyst for the one‐pot allylation reaction of aromatic aldehydes with allyltriethoxysilane under mild and simple conditions, which resulted in the direct synthesis of homoallyl ethers with very high chemoselectivity and yields. Various types of homoallyl ethers were obtained in excellent yields (up to 99%). Copyright © 2008 John Wiley & Sons, Ltd.     

A Light/Ketone/Copper System for Carboxylation of Allylic C−H Bonds of Alkenes with CO2

A photo‐induced carboxylation reaction of allylic C?H bonds of simple alkenes with CO₂ is prompted by means of a ketone and a copper complex. The unique carboxylation reaction proceeds through a sequence of an endergonic photoreaction of ketones with alkenes forming homoallyl alcohol intermediates and a thermal copper‐catalyzed allyl transfer reaction from the homoallyl alcohols to CO₂ through C?C bond cleavage.     

BiCl3 promoted aza-Prins type cyclization: a rapid and efficient synthesis of 2,4-disubstituted piperidines

Several N-protected homoallyl amines and epoxides were subjected to an aza-Prins cyclization. A rapid and efficient BiCl₃ promoted stereoselective synthesis of trans-2,4-disubstituted piperidine derivatives was achieved.     

IBX/Sc(OTf)3-promoted one-pot oxidative conjugate addition of allyltrimethylsilane to Baylis-Hillman adducts

Baylis-Hillman adducts undergo smooth one-pot oxidative Michael addition with allyltrimethylsilane in the presence of 2-iodoxybenzoic acid (IBX)/Sc(OTf)₃ under mild conditions to afford homoallyl β-ketoesters in good yields with high 1,4-selectivity.     

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.     

Synthesis of tetrahydroindolones and tetrahydrocarbazolones via palladium catalyzed C–H activation

The treatment of bromo homoallyl pyrrolyl/indolyl ketone derivatives with Pd(OAc)₂ in the presence of PPh₃ and Cs₂CO₃ in DMF resulted in the formation of tetrahydroindolones and tetrahydrocarbazolones in moderate to good isolated yields.     

Electroreductive coupling of methallylchloride or methyl chloroacetate with carbonyl compounds catalyzed by nickel bipyridine complexes

An efficient electrosynthesis of homoallyl alcohols or β-hydroxy esters in the presence of catalytic amounts of the NiBr₂(2,2′-bipyridine) complex has been developped from mixed electrolysis of methallylchloride, or methylchloroacetate with several carbonyl compounds, using a one-compartment cell equiped of a sacrificial zinc anode.     

Highly enantioselective synthesis of (+)- and (−)-perfluoroalkyl(aryl) homoallyl alcohols

Asymmetric allylboration of perfluoroaldehydes and fluorine substituted aromatic aldehydes with ^dIpc₂BAll and 2-Icr₂BAll has been investigated. Both enantiomers of the fluorinated homoallyl alcohols were obtained in high yields and excellent enantiopurity (95–99% ee).     

A general and mild copper-catalyzed three-component synthesis of protected homoallyl amines

A mild and highly efficient copper-catalyzed, one-pot, three-component reaction is developed for the synthesis of homoallyl amines. Reaction of an aldehyde, a carbamate, and allyltrimethylsilane in the presence of 5 mol % Cu(OTf)₂ furnishes the corresponding protected homoallylic amines in good to excellent yields.     

Pd-catalyzed nucleophilic allylic alkylation of aliphatic aldehydes by the use of allyl alcohols

Under catalysis of Pd(OAc)₂-(P-n-Bu)₃, Et₂Zn promotes a variety of allyl alcohols to undergo nucleophilic allylation of aliphatic aldehydes and ketones at room temperature and provides homoallyl alcohols in 60-90 and ca. 60% isolated yield, respectively. The reaction is irreversible and kinetically controlled, and unique regio- and stereoselectivities observed for the allylation with unsymmetrically substituted allyl alcohols are discussed.     

Pd-catalyzed cycloisomerization-allylation of 4-alkynones: synthesis of 5-homoallylfuran derivatives

In the presence of Pd₂(dba)₃-tBu₃P catalyst and Cs₂CO₃, cycloisomerization-allylation reactions of 4-alkynone derivatives with allyl carbonates in MeCN proceed in 5-exo mode to give highly-substituted furans having homoallyl groups at 5-position.     

Highly efficient water promoted allylation and propargylation of arylepoxides via rearrangement-carbonyl addition

A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl₂ and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields.     

Synthesis of oxazoles through Pd-catalyzed cycloisomerization-allylation of N-propargylamides with allyl carbonates

In the presence of Pd₂(dba)₃-Cy₃P catalyst, IPr·HCl salt [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], and Cs₂CO₃, N-propargylamides react with allyl carbonates to give 2,5-disubstituted oxazoles having homoallyl groups through the tandem cycloisomerization-allylation.     

Tuning the reactivity of organotin(IV) by LiOH: allylation and propargylation of epoxides via redox transmetalation

In presence of catalytic Pd(0) or Pt(II), a reagent combination of SnCl₂-LiOH promotes the reaction of organic halides and epoxides in dichloromethane leading to the regioselective formation of corresponding homoallyl and homopropargyl alcohols in good yields. This 2-carbon extension strategy adds to the repertoire of Barbier reactions via metal salts and reinforces views on the enhanced reactivity of organotin having -OH pendant.     

Trapping of Tricarbonyl(η1,η2‐homoallyl)iron and Tricarbonyl(η3‐allyl)iron Anion Intermediates with 2‐(Phenylsulfonyl)‐3‐phenyloxaziridine

The addition of reactive carbanions to (η⁴‐1,3‐diene)Fe(CO)₃ complexes at ?78 °C and 25 °C produced putative homoallyl and allyl anion complexes, respectively. Reaction of the reactive intermediates with 2‐(phenylsulfonyl)‐3‐phenyloxaziridine afforded nucleophilic substituted (η⁴‐1,3‐diene)Fe(CO)₃ complexes.     

Formation of an η-allyl and a cyclic γ-hydroxyalkyl complex of molybdenum from reaction of MoH2(η-cyclopentadienyl)2 with homoallyl alcohol

The reaction of Cp₂MoH₂ (Cp=η⁵-C₅H₅) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η³-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η³-crotyl complex.     

Iodine-catalyzed one-pot three-component synthesis of homoallyl benzyl ethers from aldehydes

Iodine has been found to be an effective catalyst for one-pot synthesis of homoallyl benzyl ethers under mild reaction conditions. Various homoallyl benzyl ethers were synthesized in moderate to high yield by three-component condensation of aldehydes, benzyloxytrimethylsilane, and allyltrimethylsilane in presence of iodine (10 mol %) in dichloromethane at 0 °C.     

Pd(OAc)2/P(cC6H11)3-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation

Allylations of aryl halides take place upon treatment of tertiary homoallyl alcohols with aryl halides in the presence of cesium carbonate and a palladium catalyst. The allylation reaction would consist of the following steps: (1) oxidative addition of aryl halide to palladium, (2) ligand exchange between the halide and the homoallyl alcohol affording aryl(homoallyloxy)palladium, (3) retro-allylation of the palladium alkoxide to generate sigma-allyl(aryl)palladium with concomitant liberation of the relevant ketone, and (4) productive reductive elimination. Since the retro-allylation step proceeds in a concerted fashion via a conformationally regulated six-membered cyclic transition state, the allylation reactions are highly regio- and stereospecific when homoallyl alcohols having a substituted allyl group are used. Whereas triarylphosphine is known to serve as a ligand for the palladium-catalyzed allyl transfer reactions, tricyclohexylphosphine proves to significantly expand the scopes of aryl halides to electron-rich aryl chlorides and of homoallyl alcohols to cyclic homoallyl alcohols. The new arylative ring-opening reactions of cyclic homoallyl alcohols allow for the synthesis of ketones having a branched or linear allylarene moiety at the remote terminus in regio- and stereospecific manners.