Chiral Sulfones Research Articles

Chiral Sulfur Ylides for the Synthesis of Bengamide E and Analogues

A new synthetic methodology of asymmetric epoxidation developed in our laboratories has been employed for the stereoselective synthesis of bengamide E (16) and analogues at the terminal olefinic position. In the event, the chiral sulfonium salt 30 was transformed into its corresponding sulfur ylide and reacted with aldehydes 21 and 44 to efficiently provide epoxy amides 31 and 45, respectively. To access the bengamides from these epoxy amides, we combined a synthetic strategy previously reported by us, using an olefin cross metathesis reaction to introduce various alkyl substituents at the terminal olefinic position of amide 33, with reactions mediated by palladium (Negishi or Suzuki couplings) from amide 49. This latter route of introduction of alkyl groups proved to be more efficient than the metathesis approach and allowed access to the generation of a wide array of new bengamide analogues.

Application of amide-stabilized sulfur ylide reactivity to the stereodivergent synthesis of ( R, S)- and ( S, R)-reboxetine

A simple access to ( R, S)- and ( S, R)-reboxetine from a single chiral sulfonium salt 4 is reported. This approach, based on a stabilized sulfur ylide-mediated epoxidation, followed by a regioselective opening reaction, enables the preparation of these two potentially biologically active compounds in 35.6% and 13.7% overall yield.

Synthesis of Prostaglandin and Phytoprostane B1 Via Regioselective Intermolecular Pauson−Khand Reactions

A new approach to the synthesis of prostaglandin and phytoprostanes B(1) is described. The key step is an intermolecular Pauson-Khand reaction between a silyl-protected propargyl acetylene and ethylene. This reaction, promoted by NMO in the presence of 4 A molecular sieves, afforded the 3-tert-butyldimethylsilyloxymethyl-2-substituted-cyclopent-2-en-1-ones (III) in good yield and with complete regioselectivity. Deprotection of the silyl ether, followed by Swern oxidation, gave 3-formyl-2-substituted-cyclopent-2-en-1-ones (II). Julia olefination of the aldehydes II with the suitable chiral sulfone enabled preparation of PPB(1) type I and PGB(1).

Catalytic enantioselective conjugate additions with α,β-unsaturated sulfones

We describe the development of a highly efficient catalytic asymmetric conjugate addition to α,β-unsaturated sulfones. Utilizing practical bifunctional organic catalysts and involving air- and moisture-tolerant conditions, conjugate additions of a wide range of Michael donors to α,β-unsaturated sulfones proceeded in excellent enantioselectivity/diastereoselectivity and high yield. This efficient and operationally simple new catalytic asymmetric reaction should provide a versatile approach for the asymmetric synthesis of chiral sulfones bearing all-carbon quaternary stereocenters.

Asymmetric syntheses and structure elucidation of cystothiazole A metabolites of the myxobacterium Cystobacter fuscus

Convergent syntheses of (14 R,15)- and (14 S,15)-dihydroxycystothiazole A 4 were achieved based on a Julia-Kocienski coupling between the functionalized aldehyde (2 E)- 6 or (2 Z)- 6, corresponding to the left-side, and chiral sulfones (14 R)- 16 and (14 S)- 16, bearing a bithiazole moiety corresponding to the right-side, respectively. The absolute configuration of natural (14,15)-dihydroxycystothiazoles A 4 was determined to be (4 R,5 S,14 S) by comparison of the physical data, including the sign of specific rotation, between synthetic (2 E,4 R,5 S,6 E,14 S)- 4 and natural 4. Deprotections of the silyl group and cyclopentane moiety of the coupled product (2 E,4 R,5 S,6 E,14 R)- 17 gave (14 R,15)-dihydroxycystothiazole C 5, which was consistent with natural 5 corresponding to the minor isomer, including the sign of specific rotation. Likewise, deprotection of the silyl group and cyclopentane moiety of the coupled product (2 E,4 R,5 S,6 E,14 S)- 17 afforded (14 S,15)-dihydroxycystothiazole C 5, which was consistent with natural 5 corresponding to the major isomer, including the sign of specific rotation. Finally, convergent synthesis of 14-hydroxycystothiazole C 3 was achieved based on the modified (one-pot) Julia olefination between the aldehyde (2 Z)- 6 and bithiazole sulfone 22. The absolute configurations of natural 14-hydroxycystothiazole C 3 were confirmed to be (4 R) and (5 S). Methylation of synthetic 3 gave cystothiazole B 2.

ChemInform Abstract: Enantioselective Synthesis of Chiral Sulfones by Rh‐Catalyzed Asymmetric Addition of Boronic Acids to α,β‐Unsaturated 2‐Pyridyl Sulfones.

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Tandem Michael Addition/Ylide Epoxidation for the Synthesis of Highly Functionalized Cyclohexadiene Epoxide Derivatives

A highly efficient diastereoselective synthesis of cyclohexadiene epoxide derivatives with a multi-stereocenter has been developed via a tandem ylide Michael addition/epoxidation. By employing a chiral sulfonium ylide, up to 96% ee can be achieved in good yields.

Enantioselective Synthesis of Chiral Sulfones by Rh-Catalyzed Asymmetric Addition of Boronic Acids to α,β-Unsaturated 2-Pyridyl Sulfones

A general and efficient method for the rhodium-catalyzed enantioselective catalytic conjugate addition of organoboronic acids to alpha,beta-unsaturated sulfones is described. The success of the process relies on the use of alpha,beta-unsaturated 2-pyridyl sulfones as key metal-coordinating substrates; typical sulfones such as vinyl phenyl sulfones are inert under the reaction conditions. Among a variety of chiral ligands, Chiraphos provided the best asymmetric induction. This rhodium [Rh(acac)(C2H4)2]/Chiraphos catalyst system has a broad scope, being applicable to the addition of both aryl and alkenyl boronic acids to cis and trans alpha,beta-unsaturated 2-pyridyl sulfones. In most cases, especially in the addition of aryl boronic acids, the reactions take place cleanly and with high enantioselectivity, affording chiral beta-substituted 2-pyridyl sulfones in good yields and enantioselectivities (70-92% ee). The sense and magnitude of this enantioselectivity have been studied by DFT theoretical calculations of the aryl-rhodium insertion step. These calculations strongly support the formation of a five-membered pyridyl-rhodium chelated species as the most stable complex after the insertion into the C=C bond. These highly enantioenriched chiral sulfones are very appealing building blocks in enantioselective synthesis. For instance, the straightforward elimination of the 2-pyridylsulfonyl group by either Julia-Kociensky olefination or alkylation/desulfonylation sequences provides a variety of functionalized chiral compounds, such as allylic substituted alkenes or beta-substituted ketones and esters.

Catalytic Enantioselective Reduction of β,β‐Disubstituted Vinyl Phenyl Sulfones by Using Bisphosphine Monoxide Ligands

Synthesis of chiral sulfones: A copper–phosphine complex efficiently provided optically active alkyl phenyl sulfones by hydrosilylation at room temperature. The reduction of β,β-disubstituted vinyl sulfones in the presence of the Me-DuPhos monoxide ligand lead to excellent enantiomeric excesses and high yields (see scheme). The prepared chiral sulfones were desulfonylated and subjected to Julia olefination conditions.

Catalytic Asymmetric Conjugate Reduction of β,β‐Disubstituted α,β‐Unsaturated Sulfones

Access to a chiral sulfone: Asymmetric conjugate reduction of β,β-disubstituted α,β-unsaturated 2-pyridylsulfones with silanes under CuI/binap catalysis provides chiral sulfones with excellent chemical yields and enantioselectivities (see scheme). These enantioenriched 2-pyridylsulfones are versatile intermediates in the preparation of a wide variety of functionalized chiral compounds. binap=2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z700296_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Labeled brassinosteroids for biochemical studies

The present paper describes the results of our studies on the synthesis of brassinolide biosynthetic precursors as tools for investigations of new biosynthetic routes leading to brassinosteroids. The corresponding labeled compounds containing three or six deuterium atoms at terminal methyl group(s) of the side chain (in a position ensuring lack of isotopic exchange) were prepared starting from stigmasterol or bisnorcholenic acid. Two strategies for the construction of the carbon skeleton of the side chain were applied in this study: Claisen rearrangement of allylic alcohols and convergent synthesis based on the coupling of 22-aldehydes with appropriate chiral sulfone. More than 20 brassinolide precursors (actual or suspected) have been prepared for metabolic studies that enabled identification of new brassinosteroids and biosynthetic subpathways to brassinolide in Secale cereale and Arabidopsis thaliana.

Enantioselective Synthesis of Vinylcyclopropanes and Vinylepoxides Mediated by Camphor-Derived Sulfur Ylides: Rationale of Enantioselectivity, Scope, and Limitation

By a sidearm approach, camphor-derived sulfur ylides 1 were designed and synthesized for the cyclopropanation of electron-deficient alkenes and epoxidation of aldehydes. Under the optimal conditions, the exo-type sulfonium salts 4a and 4b reacted with beta-aryl-alpha,beta-unsaturated esters, amides, ketones, and nitriles to give 1,3-disubstituted-2-vinylcyclopropanes with high diastereoselectivities and enantioselectivities. When the endo-type sulfonium salts 5a and 5b were used, the diastereoselectivities were not changed, whereas the absolute configurations of the products became the opposite to those of the reactions of 4a and 4b. An ylide cyclopropanation of chalcone derivatives with phenylvinyl bromide in the presence of catalytic amount of chiral sulfonium salts 4b and 5b has been developed. The sidearmed hydroxyl group was found to play a key role in the control of enantioselectivity and diastereoselectivity. The origins of the high diastereoselectivity and enantioselectivity were also studied by density functional theory calculations, which reveal the importance of the hydrogen-bonding between the sidearmed hydroxyl group and the substrate in determining the diastereoselectivity and enantioselectivity. The ylides 1 were also successfully applied for the epoxidation of aromatic aldehydes.

(S)‐Dimethylsulfonium(p‐tolylsulfinyl)methylide: A New Chiral Sulfonium Ylide and Its Use in Asymmetric Epoxidation.

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Design of Sulfides with a Locked Conformation as Promoters of Catalytic and Asymmetric Sulfonium Ylide Epoxidation

[reaction: see text] A new generation of 2,5-dimethylthiolanes with a locked conformation was developed to promote the asymmetric addition of chiral sulfonium ylides to aldehydes. The novel chiral sulfur derivative 4 succeeded the synthesis of trans-stilbene oxide derivatives with enantiomeric ratios ranging from 95:5 to 98:2. This user-friendly organocatalytic process proved to be efficient with 20-10% of sulfide 4 in 1 or 2 days of reaction. An insight into the ylide intermediate conformation is given on the basis of a computational ab initio study.

Chiral Acetylenic Sulfoxide in Organic Synthesis: Addition of Chiral Secondary Amines

Chiral secondary amines of the 3,4-dimethoxyphenylethyl and the tryptamine system were reacted with chiral acetylenic sulfoxides and achiral acetylenic sulfone. In the case of 3,4-dimethoxyphenylethyl amine, much improved diastereoselectivity (96 : 4) was observed as compared to the reaction of achiral secondary amine with chiral acetylenic sulfoxides.

Insight into the Polar Reactivity of the Onium Chalcogen Analogues of S-Adenosyl-l-methionine

S-Adenosyl-L-methionine (AdoMet) is one of Nature's most diverse metabolites, used not only in a large number of biological reactions but amenable to several different modes of reactivity. The types of transformations in which it is involved include decarboxylation, electrophilic addition to any of the three carbons bonded to the central sulfur atom, proton removal at carbons adjacent to the sulfonium, and reductive cleavage to generate 5'-deoxyadenosyl 5'-radical intermediates. At physiological pH and temperature, AdoMet is subject to three spontaneous degradation pathways, the first of which is racemization of the chiral sulfonium group, which takes place in a pH-independent manner. The two remaining pathways are pH-dependent and include (1) intramolecular attack of the alpha-carboxylate group onto the gamma-carbon, affording L-homoserine lactone (HSL) and 5'-methylthioadenosine (MTA), and (2) deprotonation at C-5', initiating a cascade that results in formation of adenine and S-ribosylmethionine. Herein, we describe pH-dependent stability studies of AdoMet and its selenium and tellurium analogues, Se-adenosyl-L-selenomethionine and Te-adenosyl-L-telluromethionine (SeAdoMet and TeAdoMet, respectively), at 37 degrees C and constant ionic strength, which we use as a probe of their relative intrinsic reactivities. We find that with AdoMet intramolecular nucleophilic attack to afford HSL and MTA exhibits a pH-rate profile having two titratable groups with apparent pK(a) values of 1.2 +/- 0.4 and 8.2 +/- 0.05 and displaying first-order rate constants of <0.7 x 10(-6) s(-1) at pH values less than 0.5, approximately 3 x 10(-6) s(-1) at pH values between 2 and 7, and approximately 15 x 10(-6) s(-1) at pH values greater than 9. Degradation via deprotonation at C-5' follows a pH-rate profile having one titratable group with an apparent pK(a) value of approximately 11.5. The selenium analogue decays significantly faster via intramolecular nucleophilic attack, also exhibiting a pH-rate profile with two titratable groups with pK(a) values of approximately 0.86 and 8.0 +/- 0.1 with first-order rate constants of <7 x 10(-6) s(-1) at pH values less than 0.9, approximately 32 x 10(-6) s(-1) at pH values between 2 and 7, and approximately 170 x 10(-6) s(-1) at pH values greater than 9. Degradation via deprotonation at C-5' proceeds with one titratable group displaying an apparent pK(a) value of approximately 14.1. Unexpectedly, TeAdoMet did not decay at an observable rate via either of these two pathways. Last, enzymatically synthesized AdoMet was found to racemize at rates that were consistent with earlier studies (Hoffman, J. L. (1986) Biochemistry 25, 4444-4449); however, SeAdoMet and TeAdoMet did not racemize at detectable rates. In the accompanying paper, we use the information obtained in these model studies to probe the mechanism of cyclopropane fatty acid synthase via use of the onium chalcogens of AdoMet as methyl donors.

New amino acid-based anionic surfactants and their use as enantiodiscriminating lyotropic liquid crystalline NMR solvents

New amino acid-based anionic surfactants have been synthesized and their use as chiral oriented NMR solvents studied. A series of sulfonated amphiphilic l-Phe or l-Ala derivatives with pentyl to tetradecyl tails were prepared by reacting the corresponding amino acid esters with o-sulfobenzoic anhydride. Their critical micelle concentrations (CMCs) range from 1.6 × 10 −5 to 1.4 × 10 −2 mol/L and depend on the alkyl chain length as well as on the nature of the amino acid block. These values are comparatively lower than those of classical surfactants such as alkylbenzenesulfonates and N-acylamino acid carboxylates. Their use as chiral liquid crystals (CLC) for analytical purposes is reported. In particular, it is shown that aqueous solutions of these chiral sulfonates in the presence of chlorinated solvents (CHCl 3, CH 2Cl 2, C 2H 2Cl 4, or CCl 4) provide homogeneous oriented NMR solvents able to differentiate between enantiomers of d, l-alanine-2- d 1 using proton and deuterium NMR spectroscopy.

Chiral sulfide-mediated enantioselective epoxidation of aldehydes

Non-racemic epoxides were prepared via enantioselective Corey-Chaykovsky epoxidation of aromatic, heteroaromatic and cinnamic aldehydes with chiral sulfonium ylides. One-pot epoxidation using aldehydes, alkyl bromides and chiral sulfide in the presence of a base was also investigated. The chiral sulfide was easily synthesized in five steps from d-camphor through hetero Diels-Alder reaction as a key step.

Synthesis and Muscarinic M2 Subtype Antagonistic Activity of Unnatural ent‐Himbacine and an Enantiomeric Pair of (2′S,6′R)‐Diepihimbacine.

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A Practical Approach Towards the Asymmetric Synthesis of α,γ‐Substituted γ‐Sultones.

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