Stereoelective Conversion of Ethyl Pipecolinate into (±)-α- and (±)-β-Conhydrins

Reaction of ethyl N-benzhydrylpipecolinate with ethylmagnesium bromide in the presence of catalytic amount of titanium(IV) isopropoxide furnished in a high yield the corresponding hydroxypropyl-substituted piperidine that by treating with alcoholic alkali was quantitatively converted into 1-benzhydryl-2-propionylpiperidine. The reduction in the latter of carbonyl group with lithium aluminum hydride or sodium borohydride in methanol gave rise prevailingly to threo-aminoalcohol. With sodium borohydride in the presence of cerium chloride an erythro-aminoalcohol was the main product. Deprotection of the nitrogen atom from the benzhydryl group of the aminoalcohols obtained provided racemic - and -conhydrines.     

New Acyclic β-Functionnalized (E) Allyl Alcohols and their Bromomethyldimethylsilyl Ethers as Cyclopentanoids Precursors

The syntheses of new acyclic (E) allyl alcohols β-functionnalized by various radical trapping functions and their corresponding bromomethyl-dimethylsilyl ethers are reported.     

Enantioselective synthesis of (S)- and (R)-α-methylserines: application to the synthesis of (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinals

This report describes the synthesis of enantiomerically pure (S)- and (R)-α-methylserines on a multigram scale, starting from the Weinreb amide of 2-methyl-2-propenoic acid and using a stereodivergent synthetic route that involves a Sharpless asymmetric dihydroxylation reaction. As a synthetic application of these quaternary α-amino acids, they were used as starting materials in the synthesis of the well-known valuable homochiral (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinal building blocks.     

Novel Cellulose Ethers: Synthesis and Structure Characterization of 3-Mono-O-(3′-hydroxypropyl) Cellulose

Summary: The synthesis of 3-mono-O-(3′-hydroxypropyl) cellulose via 3-mono-O-allyl-2,6-di-O-thexyldimethylsilyl cellulose was studied. Conversion of the double bond with 9-borabicyclo[3.3.1]nonane and subsequent alkaline oxidation lead to the 3′-hydroxypropyl group. Finally, the treatment with tetrabutylammonium fluoride trihydrate yields the complete cleavage of the protecting groups. The structure of the polymer was confirmed by one- and two dimensional NMR spectroscopic techniques. 3-mono-O-(3′-hydroxypropyl) cellulose is soluble in water and aprotic-dipolar organic media.     

Structural Characterization of Poly(α-Fluoroacrylonitrile) and Poly(Ethyl α-Fluoroacrylate)

Abstract

Monomers α-fluoroacrylonitrile (FAN) and ethyl α-fluoroacrylate (EFA) and homopolymers poly(α-fluoroacrylonitrile) (PFAN) and poly-(ethyl α-fluoroacrylate) (PEFA) have been synthesized and spectroscopi-cally characterized in detail for the first time. The ¹³C- and ¹⁹F-NMR spectroscopic results are reported, and the results are correlated to the tacticity and microstructure of both homopolymers. The major portion of the polymers is atactic. TGA analysis of PFAN indicates that the polymer is stable to about 200°C with subsequent loss of HF. PEFA is stable to 300 °C. Molecular weights determined by intrinsic viscosity (M_v ) are found to be about 130,000 for PFAN, and GPC analysis of PEFA indicates a molecular weight (M_n ) of about 36,000. Dielectric permittivities (ε) for PFAN and PEFA were determined to be 8.9 and 4.0, respectively, at 50 Hz.     

Cadmium(II) complex with (1′H-[2,2′]biimidazoly-1-YL)-acetic acid: Synthesis, crystal structure, and luminescence

A new cadmium(II) complex with (1′H-[2,2′]Biimidazoly-1-yl)-acetic acid (HBDAC) [Cd(BDAC)₂(H₂O)₂]·H₂O is synthesized and structurally characterized, which crystallizes in the monoclinic system, space group P2₁/c, a = 8.465(3) Å, b = 14.164(5) Å, c = 11.294(3) Å, α = 90°, β = 127.405(17)°, γ = 90°, Z = 2. The [Cd(BDAC)₂(H₂O)₂]·H₂O units are further bridged by O-H…O, N-H…O, C-H…O hydrogen bonds, π-π stacking and C-O…π interactions, generating a three-dimensional supramolecular structure. In addition, luminescence measurements reveal that complex 1 exhibits strong fluorescent emission in the solid state at room temperature.     

Termite Trail Attractants: New Syntheses of Racemic (E)-α-, (Z)-α- and β-Bisabolenes

Racemic (E)-α-bisabolene (E)(1) was synthetized starting from 4-methyl-3-cyclohexenecarboxylic acid (3) by a reaction sequence involving the Pd(0)-catalyzed cross-coupling reaction between the (E)-2-methyl-1-alkenyltrimethylstannane 8 and 3-methyl-2-buten-1-yl acetate (9). Three different procedures, in which a common precursor was used as key intermediate, were tested for the synthesis of racemic (Z)-α-bisabolene (Z)(1). The best one, which involved the reaction between bromide 18 and lithium dialkenylcuprate 19, afforded a mixture of (Z)- and (E)-1 in a 93 : 7 molar ratio, respectively. Finally, racemic β-bisabolene (2) was synthetized by a simple reaction sequence involving the Zr-promoted methylenation of ketone 22 prepared from 3.     

Novel Domino Reactions of (Z,Z)-2,2′-Thiobis(1,3-diarylprop-2-en-1-ones) with Acetylacetone and Ethyl Acetoacetate: Stereoselective Synthesis of Highly Functionalized Dihydrofurans

The domino reactions of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) with acetylacetone and ethyl acetoacetate in the presence of sodium ethoxide afforded the corresponding 4,5-dihydrofurans stereoselectively in moderate yields presumably via a Michael addition–enolization–displacement sequence.     

Ethyl 2-(α-hydroxyhexafluoroisopropyl)acrylate as a potential precursor of fluorine- and sulfur-containing CH-acids

The reactivity of ethyl 2-(α-hydroxyhexafluoroisopropyl)acrylate (1) was studied. The addition of thioacetic acid to compound1 occurs at 20°C, while reactions with thiols proceed only at 120°C and are accelerated in the presence of an acid catalyst. Dealkylation of acrylate1 with iodotrimethylsiliane affords 4,4,4-trifluoro-3-hydroxy-2-iodomethyl-3-trifluoromethylbutyric acid, which served as the starting compound for the synthesis of 3-chloro-4,4,4-trifluoro-2-iodomethyl-3-trifluoromethylbutyroyl chloride, a potential precursor of alicyclic fluorine- and sulfur-containing CH-acids.     

Bifunctional Silyl Triflates in Synthesis,Part 1: Synthesis and Characterization of Novel Alkane-α,ω-diyl-bis(silyl triflates)

We report the preparation of two bifunctional silyl triflates, 1,1,4,4-tetramethyl-1,4-disila-1,4-butanediyl-bis(trifluoromethanesulfonate) and 1,1,5,5-tetramethyl-1,5-disila-1,5-pentanediyl-bis(trifluoromethanesulfonate). Detailed synthetic procedures and characterization data are described.     

A Novel Synthesis of (-)-10-epi-α-Cyperone

The eudesmane derivative, (-)-10-epi-α-cyperone 1, is widely used as a chiral starting material for the synthesis of other fused-ring sesquiterpenes1. The first synthetic work was reported by Howe and co-workers via condensation of (+)-dihydrocarvone 2 with 1-diethylaminopentan-3-one methiodide in 32% yield2. Previously, our group reported the synthesis of compound 1 by treating ketone 2 with ethyl vinyl ketone (EVK) directly under different conditions1a, but the yields were not satisfacto…     

New and Concise Approach to (R)-α-Lipoic Acid

A concise enantiospecific synthesis of (S)-6,8-bis(methylsulfonyloxy)-octanoic acid (2), a ready precursor of (R)-(+)-α-lipoic acid (1), is reported. The key step of the synthesis is the coupling of the tosylate derived from (R)-malic acid with phenylpropyl magnesium bromide. A recently reported green procedure was used for the oxidative unmasking of the phenyl group, used as a latent carboxyl group.     

Possible conformations of the seven-membered rings and relative stabilities of 1β,5α,6β,7α(H)- and 1α,5α,6β,7α(H)-guai-11(13)-en-6,12-olides

A calculation has been made by the method of molecular mechanics, using the MM2 program, of a number of stereomeres of 1,5,6,7(H)- and 1,5,6,7(H)-guai-11(13)-en-6,12-olides. The possibilities of the adoption by the seven-membered ring of particular conformations according to the type of its linkage with the 5-membered carbocycle have been considered. Questions of the influence of the orientation of the Me groups on the degree of distortion of the conformation of the seven-membered ring from the ideal and the relative stabilities of the various conformers are discussed.A. N. Nesmeyanov Institute of Organometallic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 198–203, March–April, 1991.     

The Syntheses of 4,4′-(1,n-Dioxaalkane)-bisbenzaldehydes and 4,4′-(1,n-Dioxaalkane)-bis(α-methoxy Phenylacetic Acids)

The syntheses of 4,4′-(1,n-dioxaalkane)-bis(α-methoxyphenylacetic acids) were conducted using a base-catalyzed reaction. The reactants were potassium hydroxide (or lithium hydroxide/lithium chloride), bromoform, methanol and 4,4′-(1,n-dioxaalkane)-bisbenzaldehydes. The aldehyde starting materials were prepared using the Williamson ether synthesis, by condensing p-hydroxybenzaldehyde and 1,n-dibromoalkanes with lithium hydride in ethanol. The effect of varying the hydrocarbon length in the dioxaalkane bridge unit is a significant consideration (the number of CH₂ units in the bridge varying from two to eight) in their acid salt formation.

     

New and Effective Route to N-(2-F-Alkyl Ethyl) α-Amino Acids

A new and effective procedure is described for the synthesis of N-F-alkylated α-amino acids which involves a Solid-Liquid Phase Transfer Catalysis (SL-PTC) method.     

A New Approach to the Construction of Pyrrolizidine and Indolizidine Skeleton: Enantioselective Synthesis of (1S, 7aS)-1-hydroxypyrrolizidine and (1S, 8aS)-1-hydroxyindolizidine

Pyrrolizidineandindolizidineareconunonstructura1elementsofmanynaturallyoccurringalkaloidsfoundinplantsandmicroorganisms.Thediverseandpotentbiologicalactivitiesofthesealkaloidshavedrawnmuchattentioninthestudiesoftheirpharmacologyandpreparation'.Ingeneral,mostconventionalsyntheticmethodologiesinvolvedthefinalformationofoneortwoC-Nbondsofpyrrolizidineandindolizidineskeleton'.andtheseresultedintheinefficientprotectinggroupchemistry,especiallywithrespecttohandlingtheaminoresidueTherefore.themostef…     

Novel enantioselective synthesis of trans-α-(2-carboxycycloprop-1-yl)glycines: conformationally constrained l-glutamate analogues

d- and l-α-(2-carboxycycloprop-1-yl)glycines were synthesized from trans-1,3-di(2-furyl)propenone. Conversion of the double bond to a cyclopropane is followed by the formation of an oxime ether. Enantioselective reduction of the oxime ether, separation of diastereomers and oxidation of the furane rings gave enantiomerically pure d- and l-CCG I and CCG II. The structure of oxime 7b was determined by X-ray crystal structure analysis. The key step is the oxazaborolidine catalyzed enantioselective conversion of oxime ethers to amines.     

REACTION OF α-(1H-1,2,4-TRIAZOL-1-YL)ACETOPHENONE WITH PHENYL ISOTHIOCYANATE

Reaction of α-(1H-1,2,4-triazol-1-yl)acetophenonewith phenyl isothiocyanate in the presence of a base and subse-quent alkylation leads to the ketene S,N-acetal(2),(4),(7),(8);thiazolidone(3),thiazolidine(5)and 1,3-thiazine(6),     

Asymmetric Synthesis of ω‐Bromo‐2(S)‐Methyl Acids as Precursors for Novel Arginine,Lysine, and Mercapto Residues

Abstract

A series of ω‐bromo‐2(S)‐methyl acids has been synthesized as precursors of novel arginine (Arg), lysine (Lys), and mercapto analogues. These intermediates contain α‐methyl groups and are designed to mask the N‐terminal amine when incorporated in pharmaceutically relevant peptides.