The synthesis of γ-fluoroisoleucine

Condensation of 3-fluoro-2-butanone ($\text{2}$) with alkyl diethylphosphonoacetates ($\text{4a–d}$) gave alkyl 4-fluoro-3-methyl-2-pentenoates ($\text{5a–d}$). Addition of bromine yielded alkyl-2,3-dibromo-4-fluoro-3-methylpentanoates ($\text{6a,b}$) which were dehydrobrominated to alkyl 2-bromo-4-fluoro-3-methyl-2- pentenoates ($\text{7a,b}$). Since these compounds could not be hydrogenated to the desired alkyl 2-bromo-4-fluoro-3-methylpentanoates ($\text{8a,b}$), another route was taken. The esters $\text{5a–d}$ were hydrogenated to alkyl 4-fluoro-3- methylpentanoates ($\text{11a–c}$) which were converted to their carbanions. Treatment with bromine gave esters $\text{8a–c}$, and iodine gave alkyl 4-fluoro-2-iodo- 3-methylpentanoates ($\text{12a,b}$). Esters $\text{8a–c}$ and $\text{12a,b}$ were converted to alkyl 2-azido-4-fluoro-3-methylpentanoates ($\text{13a–c}$) whose hydrogenation gave alkyl 2-amino-4-fluoro-3-methylpentanoates ($\text{14a–c}$). Hydrolysis afforded γ-fluoroisoleucine ($\text{1}$).     

Synthesis of streptococci phosphatidyl-α-diglucosyldiglyceride and related glycolipids : Application of the tetraisopropyldisiloxane-1,3-diyl (tips) protecting group in sugar chemistry. Part V

A short and convenient synthesis of phosphatidyl-α-diglucosyldiglyceride (i.e. compound $\text{8d}$) and two related Streptococci glycolipids (i.e. compounds $\text{6a}$ and $\text{6b}$) will be presented. 4',6'-Tetraisopropyl-disiloxane-1,3-diyl (TIPS) protected α-glucosyl diglyceride (i.e. compound $\text{2}$) turned out to be a suitable protected precursor. Thus, compound $\text{2}$ was selectively condensed with glucosyl bromide $\text{3}$ to afford $\text{4}$. Removal of the protecting groups from $\text{4}$ gave glycolipid $\text{6a}$. The “dynamic” properties of the TIPS pro- tecting group were utilized to convert 4',6'-TIPS protected $\text{4}$ into 3',4'- TIPS protected derivative $\text{5a}$. Compound $\text{5a}$ could then be condensed with either a stearoyl fatty acid or a phosphatidyl moiety to give the fully protected derivatives $\text{5c}$ and $\text{8a}$, respectively. Finally, removal of all the protecting groups from $\text{5c}$ and $\text{8a}$ afforded the glycolipid $\text{6b}$ and glycophospholipid $\text{8d}$, respectively.     

A new synthesis of spirobenzylisoquinolines. Analogues of sibiricine and corydaine

The reduction product of dehydrocordrastine, $\text{6}$, with di-isobutylaluminum hydride spontaneously rearranged to the spirobenzylisoquinolines $\text{7a}$ and $\text{7b}$, analogous to the alkaloids sibiricine ($\text{5a}$), corydaine ($\text{5b}$), and yenhusomidine ($\text{5c}$).     

Synthesis of phosphatidyl-β-glucosyl glycerol containing a dioleoyl diglyceride moiety : Application of the tetraisopropyldisiloxane-1,3-diyl (tips) protecting group in sugar chemistry. part IV

The preparation of phosphatidyl-β-glucosyl diglyceride $\text{12c}$ is described. The synthesis of glycophospholipid $\text{12c}$ was accomplished by using: (a) the levulinoyl group for the temporary protection of the glucose hydroxyl functions of $\text{6b}$, which could then be converted into the dioleoyl substituted derivative $\text{7c}$; (b) the tetraisopropyldisiloxane-1,3-diyl (TIPS) group to protect the 3'- and 4'-hydroxyl groups of $\text{7c}$, in a two step procedure, to afford compound $\text{8}$; (c) a 2,4-dichlorophenyl protected phosphatidic acid derivative $\text{11}$. Compound $\text{11}$ could be selectively coupled to the primary hydroxyl function of $\text{8}$ to afford the fully protected glycophospholipid $\text{12a}$. Finally, removal of the 2,4-dichlorophenyl and TIPS protecting groups from $\text{12a}$ was performed with syn-4-nitrobenzaldoximate and fluoride ions, respectively, to afford glycophospholipid $\text{12c}$.     

Synthetic studies on β-lactam antibiotics. 18. Convenient,stereocontrolled synthesis of 3-methyl 7α-methoxy-1-oxacephems

Alcohols $\text{4}$ and $\text{8}$, prepared from $\text{3}$, underwent completely stereospecific etherification to give 1-oxacephams $\text{5}$ and $\text{10}$, which were converted into the 1-oxacephem nucleus $\text{1b}$ via $\text{6}$ and $\text{1c}$. Functionalization at C-3′ in $\text{6}$ and $\text{1c}$ was unsuccessful.     

Crystal structures and magnetic properties of BaTiF5 and CaTiF5

Single crystals of BaTiF₅ and CaTiF₅ were obtained by the Czochralski and Bridgman techniques, respectively. The crystal structures were determined by X-ray diffraction; BaTiF₅: $\text{14}\text{m}\text{, a = 15.091(5)}$Å, c = 7.670(3)Å; CaTiF₅: $\text{I2}\text{c}\text{, a = 9.080(4)}$Å, b = 6.614Å, c = 7.696(3)Å, β = 115.16(3)°. Both structures are characterized by the presence of either branched or straight chains of TiF₆ octahedra. BaTiF₅ contains the unusual dimeric unit (Ti₂F₁₀)^4?. Magnetic susceptibility measurements were performed on both compounds in the temperature range 4.2 to 300 K, however, no evidence for magnetic interactions between the Ti³⁺ moments were observed.     

Synthesis and crystal structure of 1,1,1,5,5,5-hexafluoro-2-aminopentan-4-one (HFAP)

The vapour phase reaction of ammonia and hexafluoroacetylacetone leads to the formation of the new β-keto-amine C₅H₃F₆NO. Crystals of the compound are monoclinic, space group $\text{P}$2₁/$\text{n}$, $\text{a}$ = 10.01(2), $\text{b}$ = 19.33(3), $\text{c}$ = 8.40(1) Å, β = 82.27(6)°; final R = 0.044.     

Cycloaddition reactions of 1,3-benzothiazines - 6. Reactions of 1,3-benzothiazine derivatives with substituted acetyl chlorides

6, 7-Dimethoxy-2$\text{H}$-l,3-benzothiazine derivatives ($\text{1}$, $\text{8}$) react with substituted acetyl chlorides to give angularly condensed β -lactams ($\text{3a}$-$\text{d}$, $\text{10}$, $\text{11}$). The $\text{cis}$ compound $\text{11}$ was epimerised to the $\text{trans}$ derivative $\text{12}$. From the interaction of 2-phenyl-6,7-dimethoxy-4$\text{H}$-1,3-benzothiazine ($\text{7}$) and α -chloro-phenylacetyl chloride two stereoisomeric β -lactam derivatives ($\text{9a}$, $\text{b}$) were isolated, whereas in the other cases studied the reactions leading to β -lactams proved to be stereospecific. Analogous reactions of $\text{4}$-methyl-6,7-dimethoxy-2$\text{H}$-l,3-benzothiazine ($\text{5}$) furnished the enamides $\text{6a}$,$\text{c}$, $\text{d}$. Structures of the new compounds and configurations of the diastereomers were elucidated by IR and NMR spectroscopy.     

The regiochemistry of intramolecular n-alkenylnitrone additions: preparative and mechanistic implications

The opposite regiochemistry, observed for the reactions $\text{7a}$ → $\text{8a}$ and $\text{7d}$ → $\text{8d}$, as compared with additions $\text{7b}$ → $\text{9b}$, $\text{7c}$ → $\text{9c}$ and $\text{7e}$ → $\text{9e}$, supports the hypothesis that in the transition state of nitrone-olefin additions the new C,C bond is more advanced than the C,0, bond. Further examples show the superimposition of substituent effects on this intramolecular control.     

The structure of some transition metal fluorides

The structures of the solid fluorides MF₂, MF₃, MF₄ and MF₅, in which M has the coordination number 6 and belongs to the 3$\text{d}$, 4$\text{d}$- and 5$\text{d}$-periods and the Vb to VIII groups, can be divided into 3 types: (a) cubic close packing ($\text{ccp}$) of F with an MFM bridging angle of 180°; (b) hexagonal close packing ($\text{hcp}$) with an MFM-bonding angle of 132°; (c) intermediate packing between (a) and (b). The linear bridging is assumed to be a consequence of π-back bonding (or charge transfer) between $\text{p}$F-orbitals and $\text{d}$-orbitals of the metal. If such bonding is not possible then $\text{hcp}$ with the bridging angle of 132° will result. Weaker π-interactions give the intermediates (c).     

Etude cristallochimique de derives du chrome(0) : I. Structure cristalline et moleculaire du benzoate de methyle chrome dicarbonyle thiocarbonyle

The crystal and molecular structure of methylbenzoatechromium dicarbonyl thiocarbonyl has been determined by a single-crystal X-ray study. The compound crystallizes with two molecules in a unit cell of symmetry P$\text{1}$, with the following parameters: triclinic system, a = 7.108(3), b = 10.340(4), c = 8.523(3) Å; α = 89.75(6), β = 95.89(4), γ = 105.50(4)°; V = 601 ų; d_m = 1.57 ± 0.05, d_c = 1.56. The structure has been refined to R and R″ values of 0.030 and 0.038 respectively, for 1963 independent reflections. The main feature of the molecule is the C_s symmetry of the Cr(CO)₂CS group with a CrC(S) bond length of 1.792(2) Å, shorter than the CrC(O) bond length, mean: 1.849(3) Å.     

Stereo- and regioselective methods for the synthesis of three consecutive asymmetric units found in many natural products

Regio- and stereoselective methods are described for the synthesis of compounds possessing the stereochemistry of type $\text{1a}$, $\text{1b}$, $\text{1c}$, and $\text{1d}$ from the aldehyde $\text{2}$.     

High diastereoselection in the claisen rearrangement of enantiomerically pure butyrolactones

The Claisen rearrangement permits the stereoselective formation of butyrolactone $\text{5b,c}$ or $\text{13b,c}$ through the utilization of enantiomeric lactone $\text{1a}$ and enantiomeric alcohols $\text{2b}$, ent-$\text{2b}$, $\text{2c}$, and ent-$\text{2c}$.     

Synthesis of enantiomerically enriched atrolactic acid and other α-hydroxy acids

The α-anions of 2-substituted 1,3-dioxolan-4-ones derived from chiral mandelic and lactic acid ($\text{2a}$, $\text{2b}$; $\text{3a}$; $\text{10a}$, $\text{10b}$) were alkylated with high stereoselectivity. The products formed were hydrolysed to α-hydroxy acids with 65–85% e.e. ((S)(+)-$\text{5}$,$\text{7}$,$\text{9}$, (R)(–)-$\text{13}$).     

Oxidative decarboxylation of [n.2.2]propellane carboxylic acids with lead tetraacetate. rearrangement approach to bicyclo [n.2.2.]bridgehead alkenes.

Oxidative decarboxylation of [n.2.2]propellane carboxylic acids ($\text{1a}$-$\text{c}$) with lead tetraacetate gave the bicyclic acetates ($\text{2b}$, $\text{c}$) having a bridgehead double bond and/or the tricyclic acetates ($\text{3a}$, $\text{b}$) in good yields. Vapor phase thermolysis of $\text{3a}$ or $\text{3b}$ afforded the bridgehead olefin $\text{2a}$ or $\text{2b}$ quantatively.     

3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

Oxygenated limonene analogs. Preparation of tetramethylated carvone and carveols via regiocontrolled opening of tetramethyllimonene oxide.

Regioselective opening of trans epoxide $\text{2}$ gave $\text{endo}$ and $\text{exo}$ tetramethylated $\text{trans}$ carveols $\text{3t}$ and $\text{4t}$ respectively, which were oxidized to tetramethylcarvone ($\text{5}$) and its unstable exocylic isomer $\text{6}$; reduction of $\text{5}$ with DIBAH gave tetramethylated $\text{cis}$ carveol $\text{3c}$ exclusively, whilst analogus reduction of $\text{6}$ produced an epimeric mixture of $\text{4c}$:$\text{4t}$=85:15.     

Cobalt metallocycles: XIII. Preparation and x-ray crystallography of cobaltacyclopentadiene and dinuclear cobalt complexes

(η-Cyclopentadienyl)(triphenylphosphine)cobaltacyclopentadienes having an electron withdrawing substituent on the cyclopentadienyl ring, (η-C₅H₄R)(PPh₃)($\text{CoCHCHC}$H) (1b: R = COOMe; 1c: R = COMe), were prepared in reasonable yields by treatment of a solution of (η-C₅H₄R)(PPh₃)₂Co with acetylene. A non-substituted cyclopentadienyl analog (1a: R = H) was also isolated in low yield according to a similar procedure. Novel dinuclear complexes were also formed as by-products and the structure of (η-C₅H₄R)Co(PPh₂$\text{C}{}_6\text{H}{}_4\text{)(μ-C}$Me)Co(η-C₅H₄R) (2b: R = COOMe), having a μ₂,η³-benzyl moiety, was determined by an X-ray crystallographic analysis. The X-ray analyses of 1a and 1b were also carried out. Crystals of 1a are monoclinic, space group Pa, a 8.529(3), b 16.010(6), c 8.028(4) Å, β 100.31(3)°, Z = 2; crystals of 1b are monoclinic, space group P2₁/a, a 8.327(2), b 36.468(7), c 8.021(1) Å, β 98.75(2)°, Z = 4; and crystals of 2b are monoclinic, space group P2₁/c, a 10.681(2), b 30.722(7), c 8.912(1) Å, β 93.55(1)°, Z = 4. They have been refined to R = 0.034, 0.047 and 0.050, respectively.     

Etude structurale d'un nouveau tellurate alcalin: Na2TeO4. Evolution de la coordination du tellure(VI) et du cation quand on passe du cation lithium au sodium

Single crystal Na₂TeO₄ has been prepared by hydrothermal synthesis and its structure determined from three dimensional X-ray analysis. The crystal is monoclinic, space group $\text{P}\text{P2}{}_1\text{c}$ with a = 10.632(5)Å, b = 5.161(2)Å; c = 13.837(11)Å, and β = 103.27(4)°. The crystal structure is built up of chains of Te(VI)O₆ octahedra parallel to the [010] axis which can be formulated as [TeO₄]_n^2n?. All sodium cations are in very distorted octahedral coordination.     

Facile syntheses of 2,4,6-cycloheptatrienyl ketones

The synthesis of the 2,4,6-cycloheptatrienyl ketones $\text{1a}$–$\text{1e}$ by two alternative routes is reported: Route 1): The adducts $\text{3a–c}$ from the phenyl(trimethylsiloxy)-acetonitriles $\text{2a–c}$, known as “umpolung” reagents, and tropylium tetrafluoroborate are cleaved by triethylammonium fluoride to form the aromatic cycloheptatrienyl ketones $\text{1a}$–$\text{1c}$. Route 2): the phenyl, methyl, and cyclopropyl ketone ($\text{1a}$, $\text{1d}$, $\text{1e}$) are prepared by treatment of the acid chloride $\text{7}$ with the corresponding organomanganese iodides RMnI ($\text{8a}$, $\text{8d}$, $\text{8e}$). The Fe-catalyzed coupling reaction of the acid chloride $\text{7}$ with a Grignard reagent was also used for the preparation of ketone $\text{1b}$.