Synthesis of (+)-(R)-5-hydroxy-6-hydroxymethyl-7-methoxy-8-methylflavanone

The synthesis of (+)-(R)-5-hydroxy-6-hydroxymethyl-7-methoxy-8-methylflavanone is described. A new chromylation method of β-ketosulfoxide 9 leading to the Michael acceptor 12 has been developed. Dilithium tetrachlorocuprate was shown to be a very efficient catalyst for the conjugate addition reaction of phenyl magnesium bromide to the α,β-unsaturated sulfoxide 12. The instability of the obtained adducts 10 represents a limitation in terms of yield. It was confirmed that the natural flavanone leridol does not possess the structure of title compound 1.     

Intramolecular michael addition reaction to chiral vinylic sulfoxides. An enantioselective synthesis of (R)- and (S)-1,7-dioxaspiro[5.5]undecane

(R)- and (S)-1,7-Dioxaspiro[5.5]undecane ((R)-1 and (S)-1), sex pheromone of an olive fly, was each stereoselectively synthesized using an intramolecular Michael addition of hydroxyl group to a chiral vinylic sulfoxide moiety as an asymmetric induction step.     

PREPARATION OF R-(+)-3,4-DIMETHOXYBENZYL 2-METHOXY-1-NAPHTHYL SULFOXIDE AND DIASTEREOSELECTIVE ADDITION OF LITHIATED ANION OF THIS REAGENT TO CYCLIC NITRONE. ASYMMETRIC SYNTHESIS OF OPTICAL PURE ISOQUINOLINE ALKALOIDS

Abstract

The addition of the lithium carbanion of (R)-(+)-3,4-dimethoxybenzyl 2-methoxy-1-naphthyl sulfoxide 3 to cyclic nitrone 4, under kinetically controlled conditions gave isoquinoline sulfoxide derivatives 5 and 6 in high diastereoselectivities, Under equilibrium controlled conditions poor diastereoselectivity results. The chiral (R)-(+)-3,4-dimethoxybenzyl 2-methoxy-I -naphthyl sulfoxide 3 was easily prepared by the reaction of 3.4-dimethoxyben-zylmagnesium chloride 2 with (-)-(S)menthyl 2-methoxy-naphthalenesulfinate 1 in dry benzene. This methodology allows for the synthesis of the isoquinoline alkaloid (R)-(-)-norlaudanosine 8 in three efficient synthetic steps.     

Crystal and molecular structure of the levorotatory (1R,2S)-ephedrinium (S)-t-butylsulfinylacetate: a definitive proof of the absolute configuration of enantiomeric t-butyl methyl sulfoxides

The levorotatory enantiomer of t-butylsulfinylacetic acid 3 was obtained in the reaction of the α-carbanion of (+)-t-butyl methyl sulfoxide 1 with carbon dioxide. The same enantiopure form of the acid 3 was isolated from its diastereomerically pure levorotatory salt 5 with (−)-(1R,2S)-ephedrine. The structure of this salt was determined by X-ray analysis and the absolute configuration (S) at sulfur was ascribed to the t-butylsulfinylacetate anion. Consequently, the absolute configuration (S) was assigned to the acid (−)-3 and its precursor (+)-t-butyl methyl sulfoxide 1.     

Unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1-phenylethyl)octahydroquinolin-7-ones

An unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)-and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)octahydroquinolin-7-ones 1 and 2 is described. In addition, a diastereospecific intramolecular Michael reaction of 3·HCl and 4·HCl is reported.     

Chiral diphenylselenophosphoramides: a new class of chiral ligands for the titanium(IV) alkoxide-promoted addition of diethylzinc to aldehydes

Chiral C₂-symmetric diphenylselenophosphoramides 1 and 2 were prepared from the reaction of diphenylselenophosphinic chloride with (1R,2R)-(−)-1,2-diaminocyclohexane and (1R,2R)-(+)-1,2-diphenylethylenediamine, respectively, in high yields. Another novel chiral ligand 3 was prepared from the reaction of diphenylselenophosphinic chloride with (R)-(+)-1,1′-binaphthyl-2,2′-diamine using butyllithium as the base. The ligands were used as catalytic chiral ligands in the titanium(IV) alkoxide-promoted enantioselective addition reaction of diethylzinc to aldehydes.     

Bifunctional nickel precatalysts of amido-functionalized N-heterocyclic carbenes for base-free Michael reaction under ambient conditions

A series of new bifunctional nickel precatalysts, [1-(R)-3-N-(benzylacetamido)imidazol-2-ylidene]₂ Ni [R = Me (1b), i-Pr (2b), and CH₂Ph (3b)], containing a Lewis acidic metal site and a Lewis basic amido-N site in a pendent ligand sidearm, have been successfully designed for base-free Michael addition reaction. Specifically, the nickel (1–3)b complexes catalyzed the highly desired base-free Michael addition reactions of representative cyclic 5-membered β-dicarbonyl and β-ketoester substrates with a variety of activated olefinic compounds in air at ambient temperature in good to excellent yield. The nickel (1–3)b complexes were synthesized from the reactions of the corresponding imidazolium chloride salts, (1–3)a, with NiCl₂?6H₂O in presence of K₂CO₃ as a base in 55–73% yield. The density functional theory (DFT) studies performed on the nickel complexes suggested the presence of a strong Ni–NHC σ-interaction in these complexes.     

Bifunctional nickel precatalysts of amido-functionalized N-heterocyclic carbenes for base-free Michael reaction under ambient conditions

A series of new bifunctional nickel precatalysts, [1-(R)-3-N-(benzylacetamido)imidazol-2-ylidene]₂ Ni [R = Me (1b), i-Pr (2b), and CH₂Ph (3b)], containing a Lewis acidic metal site and a Lewis basic amido-N site in a pendent ligand sidearm, have been successfully designed for base-free Michael addition reaction. Specifically, the nickel (1–3)b complexes catalyzed the highly desired base-free Michael addition reactions of representative cyclic 5-membered β-dicarbonyl and β-ketoester substrates with a variety of activated olefinic compounds in air at ambient temperature in good to excellent yield. The nickel (1–3)b complexes were synthesized from the reactions of the corresponding imidazolium chloride salts, (1–3)a, with NiCl₂•6H₂O in presence of K₂CO₃ as a base in 55–73% yield. The density functional theory (DFT) studies performed on the nickel complexes suggested the presence of a strong Ni–NHC σ-interaction in these complexes.     

Simple preparation of enantiomeric Michael adducts of thiophenol to chalcones: easily available new chiral building blocks

A facile and enantioselective method for the multigram preparation of the title compounds is described. The Michael addition of thiophenols to chalcones catalyzed by (+)-cinchonine, followed by crystallization, led to the corresponding adducts 2 in up to >95% e.e. The stereoselective Beckmann rearrangement of the oxime of (+)-1,3-diphenyl-3-phenylsulfanylpropan-1-one 2a gives the anilide of (R)-(+)-3-phenyl-3-phenylsulfanylpropanoic acid (as determined by X-ray analysis) and alcoholysis leads to the corresponding enantiomerically pure ethyl ester.     

Synthesis and structure of <Emphasis Type="Italic">cis</Emphasis>-dichloro(triphenylstibine)(dimethylsulfoxide)platinum(II)

The platinum molecular complex cis-Cl₂(Ph₃Sb)(Me₂S=O)Pt (I) was synthesized by the reaction of tetraphenylstibonium chloride with potassium tetrachloroplatinate in dimethyl sulfoxide. The crystal structure of square-planar complex I was determined by X-ray crystallography. The complex contains, in addition to chlorine atoms, triphenylstibine and DMSO molecules coordinated to the central atom. The bond lengths Pt-Cl, Pt-S, and Pt-Sb are 2.308(1), 2.350(1), 2.195(1), and 2.5118(4) Å, respectively. The compound is the first example of mixed-ligand platinum(II) complex in which the coordination sphere of the central atom contains, along with dimethyl sulfoxide ligand, a tertiary stibine ligand.     

Asymmetric synthesis of (R)-[2,2-2H2]-1-aminocyclopropane-1-phosphonic acid (ACPP derivative) conformationally constrained ACC analogue using a chiral sulfinyl auxiliary

The asymmetric cyclopropanation of vinylphosphonate using (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide was applied to obtain a dideuterated cyclopropyl sulfoxide. A three-step synthesis of enantiopure (+)-(1R)-1-amino-2,2-dideuteriocyclopropanephosphonic acid (+)-17-d₂ was developed.     

Enantioselective synthesis of axially chiral 1-(1-naphthyl)isoquinolines and 2-(1-naphthyl)pyridines through sulfoxide ligand coupling reactions

Racemic 1-(1′-isoquinolinyl)-2-naphthalenemethanol rac-12 was prepared through a ligand coupling reaction of racemic 1-(tert-butylsulfinyl)isoquinoline rac-7 with the 1-naphthyl Grignard reagent 10. Resolution of rac-12 was achieved through chromatographic separation of the Noe-lactol derivatives 14 and 15, providing (R)-(−)-12 of >99% ee and (S)-(+)-12 of 90% ee. The ligand coupling reaction of optically enriched sulfoxide (S)-(−)-7 (62% ee) with Grignard reagent 10 furnished rac-12, with the absence of stereoinduction resulting from competing rapid racemisation of the sulfoxide 7. Reaction of optically enriched (S)-(−)-7 with 2-methoxy-1-naphthylmagnesium bromide was also accompanied by racemisation of the sulfoxide 7, and furnished optically active (+)-1-(2′-methoxy-1′-naphthyl)isoquinoline (+)-3b in low enantiomeric purity (14% ee). The absolute configuration of (+)-3b was assigned as R using circular dichroism spectroscopy, correcting an earlier assignment based on the Bijvoet method, but in the absence of heavy atoms. Optically active 2-pyridyl sulfoxides were found not to undergo racemisation analogous to the 1-isoquinolinyl sulfoxide 7, with the ligand coupling reactions of (R)-(+)- and (S)-(−)-2-[(4′-methylphenyl)sulfinyl]-3-methylpyridines, (R)-(+)-17 and (S)-(−)-17, with 2-methoxy-1-naphthylmagnesium bromide providing (−)- and (+)-2-(2′-methoxy-1′-naphthyl)-3-methylpyridines, (−)-18 and (+)-18, in 53 and 60% ee, respectively. The free energy barriers to internal rotation in 3b and 18 have been determined, and the isoquinoline (R)-(−)-12 examined as a ligand in the enantioselectively catalysed addition of diethylzinc to benzaldehyde; (R)-(−)-12 was also converted to (R)-(−)-N,N-dimethyl-1-(1′-isoquinolinyl)-2-naphthalenemethanamine (R)-(−)-19, and this examined as a ligand in the enantioselective Pd-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate.     

Asymmetric addition of dialkyl phosphite and diamido phosphite anions to chiral, enantiopure sulfinimines: a new, convenient route to enantiomeric α-aminophosphonic acids

Lithium or sodium dialkyl phosphites and diamido phosphites 3 undergo addition to (+)-(S)-benzylidene-p-toluenesulfinamide 2 affording N-sulfinyl-α-aminophosphonates 4 in a diastereoisomeric ratio from 63:37 to 94:6. The major diastereoisomers formed in addition of lithium dimethyl phosphite 3a and lithium bis-diethylamido phosphite 3e to (+)-(S)-2 were separated and converted into enantiopure (+)-(R)- and (−)-(S)-α-aminobenzyl phosphonic acids 5, respectively.     

Stereoselective synthesis of novel C-3 functionalized 3-sulfonyl-β-lactams: Promising biologically active heterocyclic scaffolds

An efficient and operationally simple strategy for the stereoselective synthesis of novel C-3 functionalized 3-sulfonyl-β-lactam heterocycles is described. The C-3 functionalized 3-phenyl/benzylsulfonyl-β-lactams 3/3′, 5/5′ has been synthesized via Michael addition using different Michael acceptors on trans-3-phenyl/benzylsulfonyl-β-lactams 2(a–f) using K₂CO₃ as a base and acetonitrile/DMF as solvents. The reaction furnished exclusively cis-β-lactam adducts 3(a–r) using sterically less hindered Michael acceptors. Further, the effect of steric bulk and chiralilty of Michael acceptors was explored to achieve target C-3 functionalized β-lactams 3(s-u)/3′(s-u) and 5(a–c)/5′(a–c). The structural and stereochemical analysis of novel β-lactams were carried out using FT-IR, NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹³C COSY and ¹³C DEPT-135), elemental analysis (CHNS), mass spectrometry (EIMS and LCMS) in representative cases and single crystal X-ray crystallographic studies (3e). The cis or trans configuration of the Michael acceptor (E) at C-3 was assigned with respect to C4-H.     

New synthesis of a chiral steroid cd-ring synthon by means of enantioselective double Michael addition

A new synthetic method of (+)-(1R)-acetyl-(7aR)-methyl-4-hydroinden-5-one (2) by highly enantioselective double Michael addition involving alkenylcopper-phosphine complex, 3-trimethylsilylbutenone and 2-methyl-2-cyclo-pentenone is presented.     

Novel resolution of the anthracyclinone intermediate by the use of (2r, 3r)-(+)- and (2s, 3s)-(-).1,4-bis(4-chlorobenzyloxy)butane-2,3-diol: a simple and efficient synthesis of optically pure 4-demethoxydaunomycinone and 4-demethoxyadriamycinone

(±)-7-Deoxy-4-demethoxydaunomycinone((±)-3) was found to be cleanly resolved by forming a mixture of the diastereomereic acetals((-)-9and(+)-10 or(+)-9 and(-)-10)with the title vicinal-diol(+)-or ( )-5), affording optically pure (R)-( )-3. The resolving agents (( + )- and ( )-5) were readily synthesized from unnatural(2S,3S)-(-)-tartaric acid((-)-6)or D-(-)-mannitol and natural (2R,3R)-(+)-tartaric acid((+)6), respectively. The undesired enantiomer ((S)-(+ )-3) obtained by the optical resolution could be racemized by heating with trifluoromethanesulfonic acid in aq acetic acid. Optically pure (R)-3 was elaborated to optically pure (+)-4-demethoxydaunomycinone ((+)-2b) and (+)-demethoxyadriamycinone ((+)-2a) by featuring highly stereoselective ( ? 20:1) introduction of the OH group into the C₇-position as a key step.     

One step synthesis of aziridines by the Michael type addition of free sulfimides: Preparation and absolute configuration of optically active acylaziridines

The Michael type additions of diphenyl N-unsubstituted sulfimide (free sulfimide) to various electrophilic olefins were carried out. The reaction with cis- and trans-dibenzoylethylene, dimethyl-fumarate, dimethylmaleate, benzalacetophenone and benzalacetone gave mainly the corresponding trans-2-acylaziridines and trans-enaminoketones. However, phenyl vinyl sulfone or acrylonitrile afforded not the corresponding aziridine but diphenyl-N-2-cyano or N-2-phenylsulfonylethylsulfimide, a simple Michael adduct When optically active (+)-(R)-o-methoxyphenyiphenyl free sulfimide was treated with such an α,β-unsaturated carbonyl compound as benzalacetopbenone, an optically active 2-acylazindine, i.e., (-)-trans-2-benzoyl-3-phenylaziridine was obtained in ca 30% optical purity and its absolute configuration was assigned as (2R,3S) upon chemical transformation to the configuration-ally known 2-phenyl-2-benzoylamino-1-ethanol or by comparing its CD spectrum with that of (1R,2R)-1-phenyl-2-benzoyl-cyclopropane. Meanwhile, (-)-(S)-o-methoxyphenylphenyl free sulfimide was found to react with benzalacetophenone to afford (+)-trans-2-benzoyl-3-phenylaziridine of 25% optical purity. Effects of solvent and temperature on both die distribution of the products ratio and the optical yield were examined.     

Total synthesis of (+)-negamycin and its 5-epi-derivative

(+)-Negamycin was prepared in 13 steps in an overall yield of 31% from commercially available ethyl (R)-(+)-4-chloro-3-hydroxybutanoate. The key step in the reaction sequence was a highly stereoselective asymmetric Michael addition of chiral amine (−)-21 [(1S,2R)-(−)-2-methoxybornyl-10-benzylamine] into the α,β-unsaturated carbonyl moiety of key intermediate 8, thus establishing the second chiral center in (+)-negamycin. 5-epi-Negamycin was also prepared in a similar fashion.     

Enzyme-promoted desymmetrization of bis(2-hydroxymethylphenyl) sulfoxide as a route to tridentate chiral catalysts

The desymmetrization of prochiral bis(2-hydroxymethylphenyl) sulfoxide 3 was efficiently performed via acetylation promoted by commonly available lipases. Two lipases, namely, CAL-B and LPL proved particularly efficient to give 2-acetoxymethylphenyl 2-hydroxymethylphenyl sulfoxide 4 in up to 98% yield and with up to 98% ee. On the basis of an X-ray analysis, the absolute configuration of 4 was determined as (+)-(R). The enantiomerically pure product 4 was then transformed into a series of enantiomerically pure diastereomeric 2-aminomethylphenyl 2-hydroxymethylphenyl sulfoxides 8 in which the amino groups originated from enantiomerically pure amines having additional C-stereogenic centres. Compounds 8 were examined as possible tridentate chiral catalysts in a reference reaction of diethylzinc with benzaldehyde to give the expected product, 1-phenylpropan-1-ol, in moderate yields and with ee’s of up to 50%.     

Michael Addition Reaction of Vinyl Sulfoxide with Poly(Vinyl Alcohol)

The Michael addition reaction of a series of alkyl vinyl sulfoxides (CH₂[dbnd]CH-SO-R; R = CH₃ (MVSO), C₂H₅ (EVSO), t-C₄H₉ (BVSO)) with poly(vinyl alcohol) (PVA) was carried out after investigating the model reaction with isopropyl alcohol. The addition reaction was found to proceed in the presence of sodium hydroxide as catalyst. This sulfinylation of PVA proceeded more easily with MVSO and EVSO than with BVSO, and a polymer containing up to 60 mol% sulfoxide unit was obtained with MVSO and EVSO. The solution viscosity as well as the solubility behavior of the modified PVA' having various types and contents of sulfoxide group were also examined.