Stereospecific Rearrangement Research Articles

Silicon−(Thio)urea Lewis Acid Catalysis

We present a new class of catalysts based on the combination of N,N'-diaryl(thio)ureas and weak silicon Lewis acids (e.g., SiCl(4)). Such silicon-(thio)urea catalysts effectively catalyze the stereospecific rearrangement of epoxides to quaternary carbaldehydes.

Stereocontrolled Synthesis of Contiguous C(sp3)−C(aryl) Bonds by Lanthanide(III)-Catalyzed Domino Aryl-Claisen [3,3]-Sigmatropic Rearrangements

A domino [3,3]-sigmatropic aryl-Claisen rearrangement of cyclic and acyclic bisaryloxy-substituted alkenes can be performed in high yield by using Ln(fod)(3) catalysis to obtain bisphenolic products incorporating two contiguous aryl-C(sp(3)) bonds. Stereospecific rearrangement was observed for cyclic substrates. The precursor diaryl ethers were typically synthesized from the corresponding diols by double arylation procedures using either copper catalyzed coupling of aryltrifluoroborate salts or by S(N)Ar reaction.

ChemInform Abstract: C-1, C-2 Stereospecific Rearrangements of Aldohexoses by Calcium Ion in Basic Solution.

In aqueous or methanolic solution containing Ca2+ and hydroxide ion, aldoses are rapidly epimerized at C-2. This reaction involves C-1,C-2 stereospecific rearrangement. [2-13C]-D-Mannose is formed from [1-13C]-D-glucose by this reaction.

ChemInform Abstract: A Novel Skeletal Rearrangement of 2-Azabicyclo(2.2.1)hept-5-ene-3-carboxylic Acid Derivatives into 2-Oxabicyclo(3.3.0)oct-7-en-3-ones Under Acidic Conditions.

The reaction of ethyl 2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate with aroyl chloride and the subsequent hydrolysis of the ester group provided 2-aroyl-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylic acid derivatives, which underwent a stereospecific rearrangement giving 4-aroylamino-2-oxabicyclo[3.3.0]oct-7-en-3-ones by treatment with trifluoroacetic acid. On the other hand, the reaction of 2-benzoyl-2-azabicyclo[2.2.1]hept-5-ene with trifluoroacetic acid in heated benzene afforded 1-[(benzoylamino)methyl]-1,3-cyclopentadiene which afforded a Diels–Alder cycloadduct with N-phenylmaleimide. A plausible mechanism for the rearrangement is presented.

ChemInform Abstract: Synthesis of Substituted cis-Bicyclo(3.3.0)octane-1-carbonyl Derivatives by Stereospecific Rearrangement of 1-Chloro-9- hydroxybicyclo(3.3.1)nonanes.

Abstract Substituted cis -1-formyl (or acetyl) bicyclo[3.3.0]octanes are stereospecifically obtained in high yield by a base-catalyzed rearrangement of readily accessible substituted 1-chloro-9-hydrony (or acetoxy) bicyclo[3.3.1] nonanes.

ChemInform Abstract: Stereospecific Molybdic Acid-Catalyzed Isomerization of 2-Hexuloses to Branched-Chain Aldoses.

Abstract On treatment with a catalytic amount of molybdic acid in aqueous solution, the 2-ketohexoses d -fructose, l -sorbose and d -tagatose undergo a stereospecific intramolecular rearrangement to give the corresponding 2-C-(hydroxymethyl)aldoses, 2-C-(hydroxymethyl)- d- ribose ( d -hamamelose), 2-C-(hydroxymethyl)- l -lyxose, and 2-C-(hydroxymethyl)- d -xylose, respectively. At equilibrium, the ratio of 2-ketose to 2-C-(hydroxymethyl)aldose ranged from 14:1 (fructose) to 32:1 (sorbose). A similar treatment of d -psicose failed to yield a significant amount of the corresponding branched-chain aldose. The equilibria can be shifted with the addition of boric acid to the reaction mixture; under these conditions, ratios of 3:1 and 7:1 were obserwed for d -fructose and l -sorbose, respectively. A mechanistic study with d -(3-13C)fructose afforded d -(1-13C)hamamelose, thus confirming C-3C-4 bond cleavage with concomitant C-2C-3 transposition suggested from recent studies with d -(2-13C)fructose.

Stereoselective synthesis of 4H-3,1-benzothiazines via tandem nucleophilic addition/epoxy ring-opening cyclization reactions of 2-(3-phenyloxiranyl)phenyl isothiocyanates

Tandem nucleophilic addition/epoxy ring-opening cyclization reactions of 2-(3-phenyloxiranyl)phenyl isothiocyanates to produce 4-hydroxy(phenyl)methyl-4H-3,1-benzothiazines were investigated. In the reactions, carbon, sulfur, nitrogen, and oxygen nucleophiles were introduced at the 2-position of the benzothiazines, together with the two adjacent stereogenic centers arising from the epoxy carbon centers. We also found an interesting stereospecific rearrangement of 2-(alkylamino)-4-hydroxy(phenyl)methyl- 4H-3,1-benzothiazines to 1-alkyl-3-(2-(trans-3-phenylthiiran-2-yl)-phenyl)urea.

Stereospecific Synthesis of C2 Symmetric Diamines from the Mother Diamine by Resonance-Assisted Hydrogen-Bond Directed Diaza-Cope Rearrangement

Sixteen diphenylethylenediamine analogues including those with electron donating, electron withdrawing, and sterically bulky substituents have been prepared in good overall yields (70-90%) and in enantiomerically pure form (>99% ee) by diaza-Cope rearrangement reaction. A single chiral mother diamine, ((R,R)-1,2-bis-(2-hydroxyphenyl)-1,2-diaminoethane), is reacted with appropriate aldehydes to form the initial diimines that rearrange to give all the product diimines in the (S,S) form. The daughter diamines are obtained by hydrolysis of the product diimines. Density functional theory computation shows that resonance-assisted hydrogen-bond is the main driving force behind all the rearrangement reactions. Chiral high performance liquid chromatography and circular dichroism spectroscopy show that the highly stereospecific rearrangement reactions take place with apparent inversion of stereochemistry.

Isomerization as a route to rare ketoses: the beneficial effect of microwave irradiation on Mo(VI)-catalyzed stereospecific rearrangement

Mo(VI)-catalyzed isomerization of easily accessible 2- C-(hydroxymethyl)-branched aldoses to rare ketoses was achieved in 3 min using microwave flash heating. This contribution highlights the remarkable advantages of Mo(VI) catalysis and the beneficial effects of microwave irradiation in carbohydrate synthesis. The transformation yielded the respective ketoses in good yields (46–86%). Furthermore, the potential of the Mo(VI)-catalyzed transformation was studied using a new branched 6-deoxy-aldose to prepare 7-deoxy- l- gluco-heptulose. The method is fast and useful for the preparation of rare ketoses under microwave conditions.

Syntheses of (S,S)-Reboxetine via a Catalytic Stereospecific Rearrangement of β-Amino Alcohols

The formal total synthesis of (S,S)-reboxetine has been realized by two different approaches using a stereospecific rearrangement of beta-amino alcohols catalyzed by (CF3CO)2O.

Stereospecific Rearrangement of β-Amino Alcohols Catalyzed by H2SO4

Highly enantioselective rearrangement of β-amino alcohols was realized by using a catalytic amount of H 2 SO 4 .

Synthetic studies of new CMP–sialic acid analogues applying a novel buffer-mediated rearrangement

Synthetic studies of analogues of cytidine monophosphate (CMP)–sialic acid as transition state mimics for sialylation are reported, applying selective monohydrolysis of a symmetric diester and a subsequent buffer-mediated regio- and stereospecific rearrangement we reported earlier.

Lithium-Mediated Synthesis of Substituted Diarylmethylamines

A three-step urea synthesis, stereospecific rearrangement, and urea cleavage presents a novel way of synthesizing enantiomerically pure substituted diarylmethylamines. The key step is a lithium-mediated aryl transfer from one urea nitrogen to the benzylic carbon of the other urea nitrogen. This step proceeds with high levels of stereochemical retention, leading to ureas with high enantiomeric ratios. A variety of aryl groups containing substituents with different electronic or steric properties successfully undergo transfer. Cleavage of the urea by hydrolysis or reduction produces the corresponding diarylamines in good yields.

Synthesis of DEFG Ring of Complestatin and Chloropeptin I: Highly Atropdiastereoselective Macrocyclization by Intramolecular Suzuki-Miyaura Reaction

Palladium-catalyzed intramolecular Suzuki-Miyaura reaction of linear tripeptide (23) afforded the 16-membered DEFG ring of complestatin (3) in good yield with an excellent atropdiastereoselectivity. Acidic treatment of 3 triggers a stereospecific rearrangement leading to the corresponding DEFG ring 4 of chloropeptin I.

A Disaccharide Rearrangement Catalyzed by Molybdate Anion in Aqueous Solution

Reaction of a galactosylated 2-C-(hydroxymethyl)-tetrofuranose with paramolybdate ion-exchange resin in aqueous solution at 67 degrees C gave an equililibrium mixture containing the reactant aldofuranose (42%) and a 2-ketopentofuranose galactosylated at O1 (58%). Observation of this stereospecific rearrangement supports prior arguments that substituents at C2 of the branched-chain aldofuranose reactant are located in a sterically accessible pocket of the putative dimolybdate-saccharide reactive complex during epimerization. This rearrangement provides a new and convenient route to 2-ketosugars glycosylated at the exocyclic C1 position.

Enantioselective constructions of quaternary carbons and their application to the asymmetric total syntheses of fredericamycin A and discorhabdin A

Abstract An efficient enantioselective construction of quaternary carbons including spiro carbons is an area of intense interest due to the importance of these units as components of biologically active natural products. Prominent methods are presented for the synthesis of chiral, nonracemic quaternary carbon centers by (i) stereospecific rearrangement of optically active epoxides, (ii) enzyme-catalyzed resolution, and (iii) hypervalent iodine reagent-induced ipso-substitution of para-substituted phenol derivatives. These methods were applied to the total syntheses of fredericamycin A and discorhabdin A.

Boron Trifluoride Induced, New Stereospecific Rearrangements of Chiral Epoxy Ethers. Ready Access to Enantiopure 4‐(Diarylmethyl)‐1,3‐dioxolanes and 4,5‐Disubstituted Tetrahydrobenzo[c]oxepin‐4‐ols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Boron Trifluoride-Induced, New Stereospecific Rearrangements of Chiral Epoxy Ethers. Ready Access to Enantiopure 4-(Diarylmethyl)-1,3-dioxolanes and 4,5-Disubstituted Tetrahydrobenzo[c]oxepin-4-ols

Upon treatment with BF3.Et2O at low temperature, enantiopure benzyl-type ethers of arylglycidols with electron withdrawing substituents at the skeletal aryl group and electron donating substituents at the benzyl group undergo stereospecific rearrangements of Friedel-Crafts type, leading to enantiopure 4-diarylmethyl-1,3-dioxolanes (2) or to enantiopure trans-4,5 disubstituted tetrahydrobenzo[c]oxepin-4-ols (5). The course of the reactions is controlled by the substitution pattern at the benzyl ether: While benzylic systems activated toward ipso substitution afford diarylmethanes 2 through a Friedel-Crafts reaction followed by fragmentation, benzylic systems activated toward ortho attack lead to enantiopure oxepinols 5 through a 7-endo-tet ring closure of Friedel-Crafts type.

Stereospecific rearrangement of α-hydroxyepoxide: efficient approach to the trans-bicyclo[9.3.0]tetradecane core en route to clavulactone

We document a synthetic route to trans-bicyclo[9.3.0]tetradecanes. The strategy is based on a quantitative and stereospecific Lewis acid mediated rearrangement of α-hydroxyepoxide to β-hydroxyketone, which paved the way for the synthesis of clavulactone and clavirolides.

Asymmetric Synthesis of α,α‐Disubstituted α‐Amino Acid Derivatives Featuring Stereospecific Rearrangements

AbstractFor Abstract see ChemInform Abstract in Full Text.