Zwei neue pentacyclische dimere des cycloheptatriens

Titanium - catalyzed dimerization of cycloheptatriene affords pentacyclo[7.5.0.0^2,8.0^5,14.0^7,11]tetradeca-3,12-diene, $\text{3}$, and pentacyclo[8.4.0.0^3,7.0^4,14.0^6,11]tetradeca-8,12-diene, $\text{4}$. By heating, $\text{3}$ is converted quantitatively into $\text{4}$.     

General approach for the synthesis of polyquinanes: stereospecific,regiospecific entry into the tetracyclo-[6.6.0.01,5.08,12]tetradecane system

The synthesis of tetracyclo-[6.6.0.0^1,5.0^8,12]tetradecane-4,6,11,13-tetraone $\text{12}$ is described.     

General approach for the synthesis of polyquinanes

The diborane-mediated reduction of labile β-diketones 4, 5 and 6 has been employed as the key step in the synthesis of the three polyquinanes, all-$\text{cis}$-tetracyclo-[6.6.0.0^1,5.0^8,12]tetradecane 1, all-$\text{cis}$-tricyclo[6.3.0.0^1,5]undecane 2 and all-$\text{cis}$-tetracyclo-[5.5.1.0^4,13.O^10,13]tridecane, staurane 3, respectively.     

General approach for the synthesis of polyquinenes via the weiss reaction. Preparation of the chiral tetracyclo [6.6.0.01,5.08,12]tetradecane-3,6,10,13,-tetraene

The aldol approach to construct the tetracyclic polyquinane skeleton of $\text{12}$, followed by hydroboration and the HMPA mediated dehydration of four hydroxyl groups has resulted in the facile synthesis of the chiral polyquinene, tetracyclo[6.6.0.0^1,5.0^8,12]-tetradecane-3,6,10,13-tetraene $\text{2}$. This method completely avoids the troublesome fragmentation reactions earlier encountered when the strained tetraone $\text{9}$ was reacted with nucleophilic reagents.     

On the planarity of tetracyclo [5.5.1.04,13o10,13] tridecahexaene

MINDO/3 calculations indicate that tetracyclo [5.5.1.0^4,130^10,13] tridechexaene ($\text{1a}$) is nonplanar (D₂ symmetry) in its ground state with pronounced bond alternance.     

Exo/emdo soltolysis rate ratios in constrained 2-norbornyl systems

Tetracyclol[6.2.1.0^2,6.0^5,10]undec-3-yl derivatives ($\text{6}$ - $\text{8}$) show typically high tertiary exo/endo solvolysis rate ratios, but the ratios for secondary reactants are suppressed. The rate and product data support the theory of anchimeric assistance in the parent $\text{exo}$-2-norbornyl solvolysis.     

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.     

Benzo-separated pyrazolopyrimidines: Expeditious syntheses of [3,4-g]-and [3,4-h]-linked pyrazoloquinazolinones

Syntheses for pyrazolo[3,4-g]quinazolin-8(7H)-one ($\text{8}$) and its [3,4-h]-analog 11 have been developed involving elaboration of aminoindazolcarboxylic acids $\text{15}$ and $\text{30}$ from correspondingly substituted methylnitroindazols, and subsequent anellation of the pyrimidine ring by v. Niementowski cyclization.     

Convenient new synthesis of snoutene [1] utilizing a dipolar cycloaddition of 4-phenyl-1,2,4-triazolin-3,5-dione

4-Phenyl-1,2,4-triazolin-3,5-dione readily cycloadds to Nenitzescu's hydrocarbon $\text{1}$^[6] with skeletal rearrangement. The major adduct $\text{6}$ can conveniently be transformed to the azo compound $\text{8}$, which upon photolysis or thermolysis yields up to 80 % pentacyclo[3.3.2.0^2,4,.0^3,7.o^6,8]dec-9-ene (“ snoutene ”).     

Synthesis of a tetracyclodecenone with two orthogonal π-electron systems via a 1,3-through cage elimination in a bridgehead substituted 1,3-bishomocubyl acetate

Stereoselective reduction of 1,3-bishomocubanone acetate $\text{1}$ followed by mesylation leads to an epimeric mixture of mesylates $\text{3}$. Base induced homoketonization of the anti-epimer $\text{3b}$ affords tetracyclo[5.3.0.0^2,5 O^4,8]decenone $\text{4}$.     

Functionalized 2-azabicyclo[3.3.1]nonanes. IV. synthesis of the indolo[3,2-f]morphan system.

A short route to the 2-azabicyclo[3.3.1]nonan-7-one system is described. Condensation of 4-piperidones with diethyl 2-oxopropylphosphonate, followed by catalytic hydrogenation furnished the corresponding piperidylpropanones $\text{6}$ which were cyclized with mercuric acetate in acetic acid to the target target bicyclic ketones $\text{1}$. The Fischer indole synthesis from $\text{1}$$\text{a}$ afforded regioselectively the indole [3,2-f]morphan $\text{2}$, a new heteromorphan type.     

X-ray molecular structure of the 1:1 adduct of [FeH(CO)4]− and dimethyl acetylenedicarboxylate. η3-[trans-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate

The crystal structure of a bis(triphenylphosphine)iminium salt of the 1:1 adduct of [FeH(CO)₄]^? and dimethyl acetylenecarboxylate has been determined from three-dimensional X-ray data collected by the counter method. Single crystals belong to the triclinic space space group P$\text{1}$, with two units of [C₃₆H₃₀NP₂]⁺[C₁₀H₇FeO₈]^? in a cell of dimensions: $\text{a}$ = 13.918(2), $\text{b}$ = 15.669(5), $\text{c}$ = 9.909(2) Å, $\text{α}$ = 91.22(3), $\text{β}$ = 94.83(2), and $\text{γ}$ = 77.62(2)°. The structure was refined to a conventional $\text{R}$ of 0.068 for 5373 observed

reflections. The resulting structure indicates that the complex anion is η³-[$\text{trans}$-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate, the coordination around the iron atom being described as a considerably distorted trigonal bipyramid. A comparison of the present structure with the structures of related complexes suggests that the η³-acryloyl portion is best represented as an intermediate of (η³-allyl) with the oxygen atom and (η²-olefin + η¹-acyl). The short Fe-C(acyl) length of 1.897(5) Å implies an enhanced back-donation of electrons from the iron atom to the acyl group.     

A novel ethylene-bridged spiro[3.2]Hexane

3,3-Dichlorotricyclo[5.1.0.0^1,4]oct-5-en-2-one ($\text{1}$) was prepared by addition of dichloroketene to 1,3-cyclohexadiene followed by allylic bromination and dehydrobromination.     

A stereochemical and positional isotope exchange study of the mechanism of activation of tyrosine by tyrosyl-tRNA synthetase from Bacillus stearothermophilus

Tyrosyl-tRNA synthetase from Bacillus stearothernwphilus catalyses the activation of [¹⁸O₂]-tyrosine by adenosine 5$\text{[}\text{?}$(R)α-¹⁷O]triphosphate with inversion of configuration at P_α. It also catalyses positional isotope exchange in adenosine5$\text{[}\text{?}$(β-¹⁸O₂]triphosphate in the presence of tyrosine, but not in its absence or in the presence of the competitive inhibitor tyrosinol. Together these results imply that the enzyme catalyses an associative “in line” displacement of pyrophosphate from P_α of ATP by tyrosine.     

Photochemical reaction of 5-dicyanomethylenebicyclo[2.2.2]oct-2-ene as a model for a light-energy conversion and storage system

Upon irradiation, 5-dicyanomethylenebicyclo[2.2.2]octene ($\text{3}$) gives a highly strained compound, 2,2-dicyanotricyclo[4.2.1.0^1,3]nonene ($\text{6}$) in good yield. Of additional interest is the observation that the starting material $\text{3}$ can be quantitatively regenerated from the photo-product $\text{6}$ with release of 28.8 kcal/mol.     

Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

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 ($\text{2}$).     

Structure des ions [C4H7O]+ obtenus par fragmentations du [1-methylcyclobutanol]

The mass spectra of metastable molecular and fragment ions demonstrate that the loss of CH₃^. from [1-methylcyclobutanol]^.+ leads competitively to three different ions: $\text{a}$ = protonated cyclobutanone; $\text{b}$ = [n-C₃H₇CO]⁺ and $\text{c}$ = protonated methylvinylketone.