The resolution of racemic 2-alkyl-1-aminocyclopropane-1-carboxylic acids

Practical procedures for the resolution of racemic modification of (1$\text{R}$, 2$\text{S}$)-and (1$\text{S}$, 2$\text{R}$)-1-amino-2-ethylcyclopropane-1-carboxylic acid $\text{1a}$,$\text{b}$,(1$\text{R}$, 2$\text{S}$)- and (1$\text{S}$, 2$\text{R}$)-1-amino-2-methylcyclopropane-1-carboxylic acid $\text{2a}$,$\text{b}$, and (1$\text{R}$, 2$\text{R}$)- and (1$\text{S}$, 2$\text{S}$)-1-amino-2-methylcyclopropane-1-carboxylic acid $\text{3a}$,$\text{b}$ are described; the structures as $\text{1a}$,$\text{2a}$, and $\text{3a}$ were confirmed by X-ray-crystallographic methods.     

Stereochemistry of aplidiasphingosine as proposed by the asymmetric synthesis and 13c-nmr study of sphingosine relatives

The Sharpless asymmetric epoxidation was used for the synthesis of D-$\text{erythro}$-dihydrosphingosine triacetate and (2$\text{S}$, 3$\text{S}$, 5$\text{R}$)-2-acetamino-5,9-dimethyl-8-decene-1,3-diol, whose ¹³C-NMR study coupled with biogenetic consideration enabled us to propose (2$\text{1S}$, 3$\text{S}$, 5$\text{S}$,13$\text{R}$, 14$\text{S}$)-stereochemistry for aplidiasphingosine.     

Synthesis of the natural enantiomers of ascochlorin,ascofuranone and ascofuranol

Three fungal metabolites with a common structural feature as prenylated phenols were synthesized in their naturally occurring and optically active forms: ascochlorin [(2'$\text{E}$,4'$\text{E}$,1'$\text{R}$,2'$\text{R}$,6'$\text{R}$)-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[5'-(1',2',6'-trimethyl-3'-oxo-cyclohexyl)-3'-methyl-2', 4'-pentadienyl] benzaldehyde], ascofuranone [(2'$\text{E}$,6'$\text{E}$,1'$\text{S}$)-(-)-5-chloro-2, 4-dihydroxy-6-methyl-3-[7'-(3',3'-dimethyl-4'-oxo-2'-oxacyclopentyl)-3',7'-dimethyl -2', 6'-heptadienyl] benzaldehyde] and ascofuranol [(2'$\text{E}$,6'$\text{E}$,1'$\text{S}$,4'$\text{S}$)-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[7'-(3', 3'-dimethyl-4'-hydroxy-2'-oxacyclopentyl)-3', 7'-dimethyl-2',6'-hepta-dienyl]benzaldehyde ]. (+)-Ascofuranone and (+)-ascofuranol were also synthesized. By the present synthesis the absolute configuration of the natural (-)-ascofuranol was established as (1'$\text{S}$,4'$\text{S}$).     

Synthesis of (1s,5r)-karahana ether and (1s,5r)-karahana lactone,the optically active forms of unique monoterpenes wit

(1$\text{S}$,5$\text{R}$)-(-)-Karahana ether (8,8-dimethyl-2-methylene-6-oxabi-cyclo[ 3.2.1]octane) and (1$\text{S}$,5$\text{R}$)-(-)-karahana lactone (8,8-dimethyl-2-methylene-6-oxabicyclo [3.2.1]octan-7-one) were synthesized from ($\text{S}$)-3-hydroxy-2,2-dimethylcyclo-hexanone. The natural karahana lactone was shown to be almost racemic ($\text{ca}$. 1.3 % e.e.).     

Stereochemical consequence in the elimination of β-hydroxyalkylsilanes: Stereoselective formation of (Z)- and (E)-alkylidene-γ-butyrolactones

Titanium(IV) chloride-mediated reaction of 4,5-dihydro-2-(trimethylsiloxy)-3-(trimethylsilyl)furan (1a) with acetaldehyde gave $\text{diastereomerically pure}$ (3S^*, 1′R^*)-4,5-dihydro-3-(1′hydroxyethyl)-3-(trimethylsilyl)-2(3$\text{H}$)furanone (2a), which afforded selectively either (Z)- or (E)-α-ethylidene-γ-butyrolactone (3a) under proper conditions. Facile isomerization of 2a into $\text{diastereomerically pure}$ (3S^*, 1′R^*)-4,5-dihydro-3-&{1′-(trimethylsiloxy)ethyl}-2(3$\text{H}$)furanone (4) suggests an intriguing stereochemical outcome from 2a to (E)-3a via an enolate of 4.     

Chiral synthesis of (2s,3s,7s)-3,7-dimethylpentadecan-2-yl acetate and propionate,potential sex pheromone components of the pine saw-fly neodiprion sertifer (geoff.)

A synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate ($\text{2}$) and propionate ($\text{3}$) is described. (2S)-2-Methyldecan-1-yl lithium ($\text{5}$) was reacted with (3S,4S)-3,4-dimethyl-γ-butyrolactone ($\text{6}$) to yield the ketoalcohol $\text{19}$ which upon Huang-Minlon reduction furnished (2S,3S,7S)-3,7-dimethylpentadecan-2-ol ($\text{1}$). Acylations gave the esters $\text{2}$ and $\text{3}$. The (2S)-2-methyldecan-1-yl lithium was obtained via asymmetric synthesis. The chiral lactone $\text{6}$ was obtained from (2S,3S)-trans-2,3-epoxybutane and dimethyl malonate.     

Reactions of β-substituted amines-IV: Kinetics and stereochemistry of the thermal to (r) 3-chloro-1-ethylpiperidine,and the stereo-chemical course of their reactions with nucleophiles

The rate of the thermal rearrangement of (S) 2 chloromethyl-1-ethylpyrrolidine [(S)-1a] to (R)-3-chloro-1-ethylpiperidine [(R) 2a] has been examined at three temperatures in benzene by PMR and polarimetry. The rearrangement was shown to be completely stereospecific and to obey a simple first order rate law. The calculated E_a ΔH3 and ΔS3 were 22 ± 2 $\text{kcal}\text{mole}$ (25°), 21 ± 2.5 $\text{kcal}\text{mole}$ (25°) and - 10 ± 2 e.u. (0°K) respectively. The effect of solvents having differing dielectric constants was also studied. A transition state 9'a and an ion pair intermediate 3a are suggested for the rearrangement. The stereochemical course of the reactions of (S)-1a, (R)-2a and (S)-2a with hydroxide and methoxide ions have been shown to be 100% stereospecific with an uncertainty of about 1%. The absolute configurations of all optically active reactants and products [(S)- and (R)-4a, (S)-4b (R)- and (S)-5a, (R)-5b, (S,S')-6a, (S,R')-7a and (R,R')-8a] were established by chemical correlations with known compounds or by ORD and chemical inference. The ring opening of both the primary and secondary aziridinium ion positions of 1-azonia-1-ethylbicyclo [3.1.0]hexane [(S)-3a] by nucleophiles proceeds entirely by S_N2 processes. The conversion of (R)-1-ethyl-3-hydroxypiperidine [(R)-5a] to (S)-2a. HCl with thionyl chloride in chloroform proceeds by inversion with 4.8% racemization, whereas the thermal rearrangement of (S)-1a to (R)-2a occurs with complete retention of absolute configuration.     

Isolation and structural elucidation of heliangolidin,a new sesquiterpene lactone from artemisia canariensis

A new heliangolide has been isolated from aerial parts of $\text{Artemisia canariensis}$, and identified as (6$\text{E}$,10$\text{Z}$)(3$\text{S}$,3a$\text{R}$,4$\text{S}$,lla$\text{R}$)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3$\text{H}$, 4$\text{H}$) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, ¹H and ¹³C NMR, and two dimensional ¹H-¹³C chemical shift correlations) and X-ray diffraction analysis.     

Amino-sulphur-fluorine derivatives as fluoride ion donors: preparation of three- and four-coordinated cations of sulphur (IV) and (VI) [1,2]

Pentacoordinated aminosulphur (IV) trifluorides, R₂N$\text{S}$F₃, (in this paper the lone pair in S(IV)-derivatives is always considered as a ligand) and aminosulphur(VI)-oxidetrifluorides, R₂NS(O)F₃, readily lose a fluoride ion to Lewis acids (AsF₅, SbF₅, BF₃) to give sulphur-containing cationic species [R₂N$\text{S}$F₂]⁺ and [R₂NS(O)F₂]⁺ with tetracoordinated sulphur. Tetracoordinated neutral dialkylaminosulphur(IV)-oxidefluorides, R₂N$\text{S}$(O)F, and amino-imino sulphur(IV)fluorides, R₂N$\text{S}$(=NR_f)F, give three-coordinated sulphur cations [R₂N$\text{S}$O]⁺] or [R₂N$\text{S}$NR_f]⁺.The three-coordinated sulphur(VI)cation [R₂NS(O)NR]₊ has also been formed.     

Determination of the absolute configuration at C-6 and C-7 of serricornin (4,6-dimethyl-7-hydroxy-3-nonanone), the sex pheromone of the cigarette beetle

The absolute configuration at C-6 and C-7 of serricornin was established as (6$\text{S}$, 7$\text{S}$) by synthesizing its (6$\text{R}$, 7$\text{S}$-$\text{erythro}$ and (6$\text{R}$, 7$\text{R}$-$\text{threo}$ isomers.     

Synthesis of the enantiomers of 3-hydroxy-1,7-dioxaspiro[5.5]undecane, a minor component of the olive fly pheromone

(3$\text{R}$,6$\text{R}$)-(?)-3-Hydroxy-1,7-dioxaspiro[5.5]undecane 3a and its antipode were synthesized from ($\text{S}$)-malic acid.     

Stereoselective synthesis of (1R,3S)-cis-chrysanthemic acid through microbiological reduction of 2,2,5,5-tetramethyl 1,4-cyclohexanedione.

An efficient, highly stereoselective synthesis of (1$\text{R}$,3$\text{S}$)-$\text{cis}$-chrysanthemic acid 6 is described. The crucial step of this synthesis was the microbiological reduction of dione 1 into ($\text{S}$)-ketol 2.     

Adenosine cyclic 3′,5′-(RP)- and (SP)-phosphoramidates,the first representatives of nucleoside cyclic 3′,5′-phosphoramidates derived from ammonia

Adenosine cyclic 3′,5′-phosphoramidate $\text{2}$ was synthesized by reacting adenosine cyclic 3′,5′-phosphate $\text{1}$ with POCl₃, in trimethyl phosphate for 1 h at O°C, followed by in situ treatment of the reaction mixture with a suspension of (NH₄)₂CO₃ in anhydrous DMF or pyridine or DMF/pyridine mixture for 30 min at 25° C. Diastereoisomers ($\text{R}$_P)-$\text{2}$ and ($\text{S}$_P)-$\text{2}$ the relative quantities of which depended on the solvent of (NH₄)₂CO₃ treatment, were separated by reversed phase partition chromatography. Hydrolysis of (R_P)-$\text{2}$ and (S_P)-$\text{2}$ proceeded with predominant (90% in 0.1 N HCl, 100% in 0.1 N NaOH) -P-O-C bond breaking.     

Synthesis and absolute configuration of +-lineatin,the pheromone of trypodendronlineatum

A new synthesis of (±), (+)- and (-)-lineatin (3,3,7-trimethyl-2, 9-dioxatricyclo [3.3.1.0^4,7] nonane, $\text{1}$) was achieved. The stereochemistry of (+)-lineatin was established as 1$\text{R}$, 4$\text{S}$, 5$\text{R}$, 7$\text{R}$ by an X-ray crystallographic analysis of an intermediate $\text{1}$$\text{5}$.     

New tetrahydropyrans from a marine sponge

Two new tetrahydropyrans have been isolated from the sponge Haliclona sp. From chemical and spectroscopic evidence they are shown to be (1′$\text{R}$, 2$\text{S}$, 2″$\text{E}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromethyl)-2,5-dimethyl-6-(penta-2″,4″-dienyl)-tetrahydropyran and (1′$\text{R}$, 2$\text{S}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromoethyl)-2,5-dimethyl-6-(pent-4″-enyl)-tetrahydropyran.     

A new synthesis of N-benzoyl L-acosamine

Reaction of (2$\text{R}$,3$\text{S}$)-2,3-(cyclohexylidenedioxy)butanenitrile, derived from ethyl ($\text{S}$)-lactate, with the magnesium enolate of t-butyl acetate gave the corresponding ($\text{Z}$)-β-amino acrylate derivative, which was transformed into N-benzoyl acosamine by acetylation, stereoselective hydrogenation, acidic hydrolysis, and ring-formation followed by reduction with diisobutylaluminium hydride.     

On the steric course of baker's yeast mediated reduction of alkyl 4-azido- and 4-bromo-3-oxobutyrate. Synthesis of (R)- and (S)-carnitin

Baker's yeast reduction of ethyl 4-azido- and 4-bromo-3-oxobutyrate affords (3$\text{R}$) (8) and (3$\text{S}$) (2), respectively, in high optical purity.     

Completely stereoselective synthesis of all four stereoisomeric 1-carbamoyloxy-1,3-alkadienes via anti-diastereoselective homoaldol reaction from aldehydes and a single carbon-three-unit

Lithiation of both ($\text{Z}$)- and ($\text{E}$)-3-trimethylsilyl-2-propenyl $\text{N}$,$\text{N}$-diisopropyl carbamate 2 affords the (2$\text{E}$) -lithium compound 3. Aluminium- or titanium-mediated addition to aldehydes, 4 gives (1$\text{E}$)-(3$\text{R}$*4$\text{S}$*)-enol carbamates 7. A stereospecific Peterson elimination (borontriflouride- or base-mediated) introduces the second double bond either with (3$\text{E}$)- or with (3$\text{Z}$)-configuration. So just by reagent selection for each of the two steps, (1$\text{E}$,3$\text{E}$)-, (1$\text{E}$,3$\text{Z}$)-, (1$\text{Z}$,3$\text{E}$)-, or (1$\text{Z}$,3$\text{Z}$)- dienes 8 - 11, respectively, are prepared with stereoselectivities up to > 99.7%     

Functionalized 2-azabicyclo[3.3.1]nonanes. III.1 reductive rearrangement of an hexahydro-2-oxopyrano[3,2-b]pyridine

Reduction of 5-benzoyl-8-methyl-2-oxo-3,4,4a,5,6,7-hexahydro-2H-pyrano[3,2-b] pyridine ($\text{1}$) with lithium aluminium hydride afforded (1R^*,5S^*,6R^*,9S^*)-2-benzyl-5-methyl-2-azabicyclo[3.3.1]nonane-6,9-diol ($\text{2}$).     

Stereoselective synthesis of (1R,3R,5S-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane

(1$\text{R}$,3$\text{R}$,5$\text{S}$)-1,3-Dimethyl]-2,9-dioxabicyclo[3.3.1]nonane $\text{1}$ has been stereoselectively synthesized based on a highly stereoselective method for the synthesis of 1,3-$\text{syn}$-polyol.