Selective Allylation Research Articles

Sequential Pd-Catalyzed Asymmetric Allene Diboration/α-Aminoallylation

Pd-catalyzed enantioselective diboration of prochiral allenes provides adducts which participate in highly selective allylation reactions with primary imines. The allylation product is a vinyl boronate which may be oxidized to give nonracemic Mannich products (87-97% ee). Alternatively, enantiomerically enriched homoallylic amine derivatives may be obtained by protonation and Suzuki cross-coupling of the vinyl boronate.

Selective Allylation of Arenethiols Using Water‐Soluble Palladium Complex Catalyst in Recyclable Water/Hexane Biphasic Media.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Selective Allylation of Arenethiols Using Water-soluble Palladium Complex Catalyst in Recyclable Water/Hexane Biphasic Media

Abstract Allylation of arenethiols by allylic alcohol with sterically hindered carbon of the allylic moiety is smoothly catalyzed by Pd(OAc)2/TPPTS in biphasic water/hexane media under ambient conditions. The catalyst water layer can be repeatedly reused without catalytic activity loss.

One step selective 5′- O-allylation of thymidine using microwave or ultrasound activation

An improved procedures for the synthesis of 5′- O-allylthymidine via one step selective allylation of thymidine using either ultrasound or microwave activation is described.

Unusual selective allylation of norbornadiene in the presence of palladium nanoclusters

The reaction of norbornadiene (NBD) with allyl acetate in the presence of the nanocluster Pd147phen32O60(OCOBut)30 (Pd-147; phen is 1,10-phenanthroline) and PPh3 in acetonitrile is nonselective and is accompanied by the decomposition of the cluster, affording the same allylation products of NBD as the reaction with Pd3(OAc)6 or Pd(dba)2 (dba is dibenzylideneacetone) combined with PPh3. In contrast, in the ionic liquid [bmim][BF4] (bmim is 1-butyl-3-methylimidazolinium), the Pd-147 is not decomposed and the reaction occurs selectively to give methylidene(vinyl)norbornene as the sole product. The data obtained suggest that in an ionic liquid, the reaction under study is catalyzed by the nanocluster Pd-147 rather than by the products of its decomposition.

Organic Synthesis in Solid Media. Silica Gel as an Effective and Reusable Medium for the Selective Allylation of Aldehydes with Tetraallyltin.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of tricyclic analogues of methyllycaconitine using ring closing metathesis to append a B ring to an AE azabicyclic fragment.

The synthesis of several ABE tricyclic analogues of the alkaloid methyllycaconitine 1 is reported. The analogues contain two key pharmacophores: a homocholine motif formed from a tertiary N-ethyl amine in a 3-azabicyclo[3.3.1]nonane ring system and a 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester 4. The synthesis of the ABE tricyclic analogues of MLA 1 began with selective allylation at C-3 of 3 to produce allyl beta-keto ester 4. Double Mannich reaction of 4 with ethylamine and formaldehyde produced bicyclic amine 5 The C-9 ketone of bicyclic amine 5 was selectively reduced to form bicyclic alcohols 6 and 7 which were subsequently allylated to form dienes 8 and 9. Ring closing metathesis of dienes 8 and 9 afforded tricyclic ethers 11 and 12, respectively, the C-8 ester of which was reduced to a hydroxymethyl group to form ABE tricyclic analogues 13 and 14. Addition of allylmagnesium bromide to the C-9 ketone of 20 afforded dienes 21 and 22, which underwent ring closing metathesis to form tricyclic esters 23 and 24, respectively. Reduction of the C-8 ethyl ester of 23 and 24 to a hydroxymethyl group afforded diols 25 and 26 respectively. The 2-(3-methyl-2,5-dioxopyrrolin-1-ly)benzoate ester was introduced by conversion of alcohols 13, 14, 25 and 26, to the anthranilate esters 16, 17, 27 and 28 using N-(trifluoroacetyl)anthranilic acid 15 followed by fusion with methylsuccinic anhydride to afford the substituted anthranilates 18, 19, 29 and 30 containing the key 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester pharmacophore.

Organic synthesis in solid media. Silica gel as an effective and reusable medium for the selective allylation of aldehydes with tetraallyltin

Wet silica gel promotes the chemoselective and almost complete allylation of aldehydes with 0.25–0.30 molar equivalents of tetraallyltin without an organic solvent, leaving no organotin compounds, requiring neither extraction nor chromatographic separation after the reaction, and enabling the repeated use of the silica gel.

Asymmetric synthesis of fused bicyclic alpha-amino acids having a hexahydro-cyclopenta[c]pyridine skeleton via intramolecular Pauson-Khand reaction of 1-sulfonimidoyl-substituted 5-azaoct-1-en-7-ynes.

An asymmetric synthesis of fused bicyclic amino acids having a hexahydro-cyclopenta[c]pyridine skeleton and carrying besides an enone structural element a substituent at the beta-position is described. The key steps of the synthesis are a highly selective allylation of N-tert-butylsulfonyl imino ester with bis(allylsulfoximine)titanium complexes and a highly diastereoselective Pauson-Khand cycloaddition of sulfonimidoyl-substituted gamma,delta-unsaturated alpha-amino acid esters carrying a substituent at the beta-position and a propargyl group at the N-atom. The cyclization is accompanied by a reductive cleavage of the sulfoximine group of the primary cyclization product. Surprisingly, the removal of the sulfoximine group proceeds with inversion of the configuration at the S-atom and gives N-methyl-phenylsulfinamide with >/=98% ee. Deprotection of the bicyclic N-tert-butylsulfonyl-protected amino acid ester was accomplished through treatment with CF(3)SO(3)H under anhydrous conditions. The enantio- and diastereomerically pure sulfoximine-substituted gamma,delta-unsaturated alpha-amino acid esters used as starting material were obtained through a highly regio- and diastereoselective allylation of N-tert-butylsulfonyl imino ester with acyclic bis(allylsulfoximine)titanium complexes, described previously.

Reactivity of ammonium and iminium tetraphenylborates towards Pd(0)-complexes: selective allyl or proton transfer to Pd(0).: Evidence of formation of the species [HPd(dppe) 2][BPh 4

The reactivity of ammonium- and iminium-BPh 4 salts, [CH 2CHCH 2NH 3]BPh 4, [(CH 2CHCH 2)HNCMe 2]BPh 4 and [(PhCH 2)HNCMe 2]BPh 4, towards Pd(0)-complexes, [Pd(dppe)(dba)] and [Pd(dppe) 2] (dppe=1,2-bis(diphenylphosphino)ethane; dba=dibenzylideneacetone), has been investigated. Allyl-ammonium and -iminium tetraphenylborates [CH 2CHCH 2NH 3]BPh 4 and [(CH 2CHCH 2)HNCMe 2]BPh 4 react with [Pd(dppe)(dba)] to afford, under mild conditions (293 K), [(η 3-C 3H 5)Pd(dppe)][BPh 4], through selective oxidative transfer of allyl group from the ammonium or iminium cation to the Pd center. [(PhCH 2)HNCMe 2]BPh 4 reacts with [Pd(dppe) 2] to afford [HPd(dppe) 2][BPh 4], that, under the reaction conditions, has poor stability as it undergoes hydride transfer to the iminium ion present in the reaction medium, affording [Pd(dppe) 2][BPh 4] 2.

ChemInform Abstract: Synthesis of Enantiopure Homoallylic Ethers by Reagent Controlled Facial Selective Allylation of Chiral Ketones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Novel synthesis of the allene moiety of carotenoids via biomimetic photosensitized oxygenation

A novel synthesis of the allene moiety of carotenoids was achieved by the regioselective ene reaction of the vinyl hydrogen rather than the allyl hydrogen of the significantly twisted 1,3-dienes, (3R)-alkoxy-cis-β-ionol derivative, followed by selective allyl rearrangement.

Synthesis of Enantiopure Homoallylic Ethers by Reagent Controlled Facial Selective Allylation of Chiral Ketones

The stereoselective allylation of chiral methyl ketones to give tertiary homoallylic ethers, which can easily be transformed into homoallylic alcohols, is described. Reaction of the enantiopure ketones 8 a–d and the racemic ketones 26 a–d with the norpseudoephedrine derivative 2 or ent-2 and allylsilane in the presence of a catalytic amount of trifluoromethanesulfonic acid, led to a series of homoallylic ethers with good to excellent diastereoselectivity (85:15 to >97:3). The allylation is reagent controlled and nearly independent from the stereogenic centers in the substrates. A partial kinetic resolution was observed using the racemic ketones 26 a–d. In the reaction of the chiral ketones 8 a–d with the achiral reagents ethoxytrimethylsilane and allylsilane only a low diastereoselectivity was observed.

Synthesis of Enantiopure Homoallylic Ethers by Reagent Controlled Facial Selective Allylation of Chiral Ketones

The stereoselective allylation of chiral methyl ketones to give tertiary homoallylic ethers, which can easily be transformed into homoallylic alcohols, is described. Reaction of the enantiopure ketones 8a-d and the racemic ketones 26a-d with the norpseudoephedrine derivative 2 or ent-2 and allylsilane in the presence of a catalytic amount of trifluoromethanesulfonic acid, led to a series of homoallylic ethers with good to excellent diastereoselectivity (85:15 to > 97:3). The allylation is reagent controlled and nearly independent from the stereogenic centers in the substrates. A partial kinetic resolution was observed using the racemic ketones 26a-d. In the reaction of the chiral ketones 8a-d with the achiral reagents ethoxytrimethylsilane and allylsilane only a low diastereoselectivity was observed.

Controlled Synthesis of Mono-p-[(2,3-epoxy)propyl]- and Mono-p-(2-oxoethyl)-tris-p-tert-butylcalix[4]arenes Crystal Structure Determination of an Epoxy Calix[4]arene

Four new tri-tert-butylcalix[4]arenes bearing an epoxy or a carbaldehyde function at the upper rim have been prepared by a multi-step synthetic pathway involving initial selective allylation of tris-(O-benzoyl)-tri-tert-butylcalix[4]arene, followed by either m-CPBA oxidation or ozonolysis of the allyl group. The benzoylated epoxycalixarene was obtained as single crystals, analysis of which confirmed the formation of the epoxide group and the partial-cone conformation of the macrocyclic structure.

Functionalization of Hydrocarbons by a New Free Radical Based Condensation Reaction

The Br. radical is the chain carrier of a new highly selective allylation of hydrocarbons (and other substrates): It abstracts a hydrogen atom from R−H to yield R.. Addition of R. to substituted allyl bromide (to form a β-bromo radical) followed by β-cleavage regenerates Br. and provides the product. Reaction yields and kinetic chain lengths for this reaction are highest when the allyl bromide contains a radical-stabilizing substituent.

ChemInform Abstract: Highly Selective Allylation of Alkyl Methyl Ketones in the Presence of Chiral 2‐Amino Alcohol Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly Selective Allylation of Alkyl Methyl Ketones in the Presence of Chiral 2-Amino Alcohol Derivatives

The facial selective allylation of alkyl methyl ketones 1a–f in the presence of chiral 2-amino alcohol derivatives 2a–p by reaction with allylsilane 3 and a catalytic amount of TfOH to give the tertiary homoallylic ethers 8a–o and 9a–e is described. The best results were obtained with the 2-amino alcohol derivative 2p which affords a stereoselectivity of 18:1 even for the allylation of ethyl methyl ketone. The ethers 8 and 9, which contain a phenyl group at C-1 of the amino alcohol moiety, can be cleaved to give the corresponding homoallylic alcohols 5 by reduction with sodium or lithium in liquid ammonia.

ChemInform Abstract: Three‐Component Synthesis of Homoallylamines by Scandium(III) Triflate‐Mediated Allylation with Allylgermane: A Highly Imine Selective Allylation Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Extremely Facile and Selective Nickel-Catalyzed Allyl Ether Cleavage

Extremely Facile and Selective Nickel-Catalyzed Allyl Ether Cleavage