Allylic Transposition Research Articles

Preparation of β-Substituted α-(Acetoxymethyl)cyclohex-2-en-1-ones

An effective three-step sequence for the preparation of β-substituted 2-(acetoxymethyl)cyclohex-2-en-1-ones 4, via oxydative allylic transposition of the corresponding allylic alcohols 3, is reported.

Addition of Organometallic Nucleophiles to β-Keto Phosphonates.

The reaction of some Grignard reagents with β-keto phosphonates results in nucleophilic addition to the carbonyl group to afford β-hydroxy phosphonates with extension of the carbon skeleton. Additions of allylmagnesium reagents have proven particularly efficient, especially in the presence of BF3·OEt2. Reactions of allylic zinc reagents with β-keto phosphonates also gave the desired β-hydroxy phosphonates, often in even better yields. With crotyl and prenyl organometallic reagents, the reactions proceed with allylic transposition. Because these allylation reactions expand the functionality of the original substrate, various transformations can be conducted on the initial products to provide convenient access to a variety of new phosphonates.

Baylis-Hillman reaction of N-trityl aziridine-2-( S)-carboxaldehyde

N-Trityl aziridine-2-( S)-carboxaldehyde 1 undergoes a facile Baylis-Hillman reaction with a variety of activated vinyl compounds in the presence of a catalytic amount of DABCO to furnish the corresponding adducts 2 in good yields. Unexpectedly, acetylation of the adduct 2a derived from methyl acrylate takes place using Ac 2O/py with concomitant allylic transposition. The predominant Z-isomer 4 gives a S n2 type displacement of the acetate with various nucleophiles in contrast to reported S n2′ type displacement in similar systems.

Preparation of β-Substituted α-(Acetoxymethyl)cyclohex-2-en-1-ones

An effective three-step sequence for the preparation of β-substituted 2-(acetoxymethyl)cyclohex-2-en-1-ones 4, via oxydative allylic transposition of the corresponding allylic alcohols 3, is reported.

Nickel and Palladium Catalysis in the Stereoselective Synthesis of Functionalized Pyrrolidines: Enantioselective Formal Synthesis of (+)-α-Allokainic Acid.

Neuroexcitatory natural products are accessible from 1 via the intermediate 2, which is obtained by Ni-catalyzed cyclization, transposition of the protecting group, and Pd-catalyzed reduction with allylic transposition. This stepwise formation of stereocenters allows a highly direct and stereoselective synthesis of the excitatory amino acid (+)-α-allokainic acid, which displays an all-trans arrangement of the substituents about the pyrrolidine ring. TBS=tert-butyldimethylsilyl.

Application of an S --> O Allylic Transposition in the Context of a Bridgehead Olefinic System. New Opportunities for the Structural Modification of Bicyclo[6.2.1]undecanes via Transannular Ring Closure.

A practical route is described for the preparation of allylic sulfide 8, whose double bond resides at a bridgehead site. Following hydride reduction of the ketone carbonyl and sulfoxidation, exposure to trifluoroacetic anhydride results in the operation of an intermolecular S --> O allylic transposition. This central step leads to 14a, an intermediate useful for probing the consequences associated with epoxidation of its cis-cyclononene double bond. A total of three different transannular cyclizations are described in order to demonstrate the ease with which ring closures can operate in a medium-ring setting of this type. Represented are transformations that generate tetrahydrofuran, oxetane, and cyclopropane subunits. The kinetic biases favoring these transformations are highlighted.

ChemInform Abstract: Allylic Transposition of Alcohol and Amine Functionality by Thermal or Palladium(II)‐Catalyzed Rearrangements of Allylic N‐ Benzoylbenzimidates.

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Indium‐Mediated Reactions of Enamines in the Presence of Acid

AbstractThe reaction of enamines with allyl bromide and metallic indium in THF to afford homoallylamines was greatly accelerated by the addition of one equivalent of a suitable carboxylic acid, such as acetic acid. It was established that the likely mechanism consists of a nucleophilic addition of an indium sesquihalide to the iminium salt formed by protonation of the enamine. Substituted allyl bromides also reacted with complete allylic transposition (γ‐addition). In contrast to indium‐mediated allylation of carbonyl compounds in which only two of the three allyl groups of the sesquihalide are involved, all three allyl groups are involved in the reaction with enamines. As a result only 2/3 equiv of indium are required. This allylation was also performed with zinc, tin, bismuth, and aluminum in the presence of a catalytic amount of InCl3 instead of indium. However, these reactions invariably gave lower yields. The analogous reaction of methyl bromoacetate instead of allyl bromide was also studied. This “Reformatsky‐type” process was also greatly accelerated by the addition of one equivalent of acetic acid. In this case, the yields remained moderate for both indium and zinc.

Allylic Transposition of Alcohol and Amine Functionality by Thermal or Palladium(II)-Catalyzed Rearrangements of Allylic N-Benzoylbenzimidates.

Allylic Transposition of Alcohol and Amine Functionality by Thermal or Palladium(II)-Catalyzed Rearrangements of Allylic N-Benzoylbenzimidates.

Asymmetric [2,3]-Wittig rearrangement as a general tool for asymmetric synthesis

Abstract

Total synthesis of thromboxane B 2 starting from ( R, R)-tartaric acid as a chiral pool

Optically active natural thromboxane B 2 ( TXB 2 ) was synthesized from ( R, R)-tartaric acid as only chiral source. The synthesis was achieved through regio- and stereoselective introduction of acetate moiety at the C2-position of the 6,8-dioxabicyclo[3.2.1]octene derivative ( 2) to provide an acetamide derivative ( 6), partial ring opening of 6 to give a pyranoid ( 10), and construction of the C15-hydroxyl group of TXB 2 by stereospecific allylic transposition of the inherent chirality of tartaric acid in the trans-allylic acetate ( 18).

The First Efficient Catalyzed Acylation of Allylsilanes1

In the presence of catalytic amounts (5 mol %) of BiCl3−3 NaI or BiCl3−1.5 ZnI2 acylation of allyltrimethylsilane by a variety of acyl chlorides (RCOCl with R = Me, Et, i-Pr, t-Bu, Ph, 1-adamantyl) proceeded rapidly at room temperature without decarbonylation of the acyl chloride. Allyl ketones were usually obtained in high yield with little or no isomerization to 1-propenyl ketones. Using (3-methylbut-2-enyl)trimethylsilane and Me2CCHCOCl, Artemisia ketone was synthesized in nearly quantitative yield after complete allylic transposition.

Rearrangement of α-hydroxy imines to α-amino ketones: Mechanistic aspects and synthetic applications

In refluxing diglyme, rearrangement of α-hydroxy imines bearing diversely substituted allyl groups or a 3-trimethylsilylpropargyl group on the α-carbon to the nitrogen afforded in good yields α-amino ketones. Migration of allyl or 3-trimethylsilylallyl groups occured without allylic transposition in contrast to the 1-methylallyl group. In the 3 cases studied, the rearrangement of enantioenriched α-hydroxy imines took place with complete 1,2-chirality transfer. The rearrangement was applied to the preparation of (+)-1-benzyl-1-azaspiro[5.5]undecan-7-one, a precursor in the synthesis of (−)-perhydrohistrionicotoxin.

Transformation de l'hexafluoropropène en alcool trifluoroallylique, précurseur des α-fluoroacrylates

The α-fluoroacryloyl fluoride precursor of α-fluoroacrylic acid esters can arise from an allylic transposition of trifluoroallylic alcohol of which two methods of preparation are presented. In the first, dehydrofluoration of the alcohol CF 3CFHCH 2OH ( 4) is used. This alcohol is generated from the ester CF 3CFHCOOC 2H 5 ( 3). In the second, dehalogenation of the alcohol CF 3CFBrCH 2OH ( 10) by zinc is used. The latter is formed by the selective reduction of the ester CF 3CFBrCOOC 2H 5 ( 9).

Chemistry Prospects of new Sugar-Derived Vinyl Sulfones

Abstract Major aspects of the reactivity potential of sugar-derived vinyl sulfones of type 2 were explored, including conjugate addition, desulfonylation, vinylic deprotonation, allylic transposition and dipole cycloaddition.

The First Examples of a Claisen Rearrangement Stereocontrolled by a Sulfur Center of Chirality

Abstract The asymmetric version of the Claisen rearrangement (1) usually involves the preparation of a carboxylic ester of an enantiomerically pure allylic alcohol, its deprotonation and transposition either of the lithium enolate or its silyl ketene acetal.

Chemistry Prospects of New Sugar-Derived Vinyl Sulfones

Abstract Major aspects of the reactivity potential of sugar-derived vinyl sulfones of type 2 were explored, including conjugate addition, desulfonylation, vinylic deprotonation, allylic transposition and dipole cycloaddition.

Stereoselective allylic transposition by means of allylic n-pentenyl ethers

Stereospecific formation of optically active tetrahydrofurans and dihydropyrans was obtained via an allylic rearrangement by means of allylic n-pentenyl ethers.

Nucleic acid related compounds. 77. 2′,3′-Didehydro-2′,3′-dideoxy-2′(and 3′)-methylnucleosides via [3,3]-sigmatropic rearrangements of 2′(and 3′)-methylene-3′(and 2′)-O-thiocarbonyl derivatives and radical reduction of a 2′-chloro-3′-methylene analogue

Treatment of 5′-O-(tert-butyldiphenylsilyl)-2′(and 3′)-deoxy-2′(and 3′)-methyleneuridine (and adenosine) derivatives with phenyl chlorothionocarbonate gave the 3′(and 2′)-O-phenoxythiocarbonyl intermediates, which underwent spontaneous [3,3]-sigmatropic rearrangement to give the 2′,3′-didehydro-2′,3′-dideoxy-2′(and 3′)-(phenoxycarbonylthio)methyl analogues. These allylic thioesters were subjected to tributylstannane-mediated hydrodesulfurization and deprotection to give 2′,3′-didehydro-2′,3′-dideoxy-2′(and 3′)-methyluridine (and adenosine). Tributylstannane-mediated hydrodehalogenation of a 2′-chloro-2′,3′-dideoxy-3′-methyleneuridine derivative afforded the 2′,3′-didehydro-2′,3′-dideoxy-3′-methyl product of allylic transposition exclusively.

The synthesis of δ-hydroxy allylic phosphine oxides by palladium(II)-catalysed allylic acetate transposition

The synthesis of δ-hydroxy allylic phosphine oxides by palladium(<scp>II</scp>)-catalysed allylic acetate transposition