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.     

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.     

Crystal growth and X-ray data of the lead phosphates Pb4P2O9 and Pb8P2O13

Single crystals of the title compounds have been grown by the Czochralski technique. Pb₄P₂O₉ crystallizes in the space group $\text{P2}{}_1\text{c}$ with the parameters a = 9.4812 Å, b = 7.1303 Å, c = 14.390 Å, β = 104.51° and Pb₈P₂O₁₃ in $\text{C2}\text{m}$ with a = 10.641 Å, b = 10.206Å c = 14.342 Å, β = 98.34°.     

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-$\text{2c}$.     

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 $\text{1b}$.     

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 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.     

Kationische cyclisierung von (Z)-und (E)-1,3-dimethyl-2-(3-hexenyl)-2-cyclohexenol

The cationic cyclization of the carbinol $\text{3a}$(Z) occurred stereoselectively and resulted in a mixture of the hydrindane $\text{4a}$ and the octalin $\text{5a}$, both with $\text{trans-}$configuration of side chain and angular methyl group. Cyclization of $\text{3b}$(E) yielded in $\text{4b}$ and $\text{5b}$, both with $\text{cis}$-configuration. The structure of $\text{4a}$,$\text{5a}$ was proved by transformation to the diketones $\text{8}$,$\text{9}$.     

Molecular rearrangements of 5-azido substituted 1,2,3-triazoles

5-Azido-4-methoxycarbonyl-1-phenyl-1,2,3-triazole ($\text{8a}$) and its phenyl substituted derivatives $\text{8b}$,$\text{c}$ rearrange at 60–80°C to give tetrazolyldiazoacetates $\text{9}$, which have been isolated. When the reactions are allowed to go to completion, products derived from the diazo compounds are obtained; i.e. norcaradienes ($\text{10}$) from benzene solutions and imidazotetrazoles ($\text{12}$) from nitrite solutions. The latter decompose photochemically into diazacyclopentadienonimines ($\text{13}$). A kinetic study of the rearrangement $\text{8}$ → $\text{9}$ has been carried out and the mechanism (Scheme VI) is discussed in comparison with the Dimroth rearrangement.     

A convenient synthesis of flindersine,atanine and their analogues

A new synthesis of the pyranoquinolone alkaloids flindersine ($\text{8a}$), 8-methoxyflindersine ($\text{8c}$), N-methylflindersine ($\text{9a}$), zanthobunglanine ($\text{9c}$) oricine ($\text{9d}$) and veprisine ($\text{9e}$) and the prenylquinolone alkaloids atanine ($\text{13a}$), preskimmianine ($\text{13e}$) N-methylatanine ($\text{14a}$), O-methylglycosolone ($\text{14c}$) and N-methylpreskimmianine ($\text{14e}$) is described.     

Syntheses of PGJ2 type analogues: 16-hydroxy-11-oxo-Δ5,9,12,14-prostatetraenoic acid t-butyl ester and its related derivatives

PGJ₂ analogues, the title compound ($\text{8c}$) and its related derivatives ($\text{8a}$, $\text{8b}$), were synthesized $\text{via}$ the three-component coupling process involving 1,4-addition reaction of phenylsulfinylallylic carbanion ($\text{2}$′) to cyclopentenone derivative ($\text{1}$) followed by trapping the generated enolate with aldehyde ($\text{3}$).     

A nitrosamine route to (±)-macrostomine

In a synthetic approach to macrostomine $\text{1}$, both side chains of the isoquinoline nucleus are attached by high yield carbon carbon bond formation with lithiated nitrosamines ($\text{2b}$ → $\text{3a}$, $\text{3c}$ → $\text{4a}$).     

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 $\text{12c}$.     

Pummerer reaction intermediate as an initiating function for cationic olefin cyclization

Treatment of N-(2-methyl-2-propenyl)-N-methyl-α-(methylsulfinyl)acetamide ($\text{6a}$) with trifluoroacetic anhydride caused the cationic olefin cyclization through a Pummerer reaction intermediate to give the six-membered lactams $\text{7}$ and $\text{8}$. Similar reaction converted N-2-butenyl-N-methyl-a-(methylsulfinyl)acetamide ($\text{6b}$) to the five-membered lactam $\text{9}$, and N-2-propenyl-N-methyl-α-(methylsulfinyl)- acetamide ($\text{6c}$) to the five-membered lactams $\text{11}$ and $\text{12}$.     

Stereoselective synthesis and Diels-Alder reactions of bis-Ether 1,3 Dienes. A further test for cooperativity during cycloaddition reactions.

A stereoselective synthesis of dienes $\text{1a}$ and $\text{1b}$, using butadiene-iron tricarbonyl complexes, is described. Higher diastereoselectivity is observed during Diels-Alder reaction of $\text{1a}$ as compared with $\text{1c}$, affording good evidence for cooperativity in these cycloadditions.     

Photocyclization of n-[ω-(cycloalken-1-yl)alkyl]-and n-[ω-(inden-3-yl)alkyl]phthalimides : Synthesis of spiro-nitrogen multicyclic systems

Photolysis of the N-[ω-(cycloalken-1-yl)alkyl]phthalimides 6b-$\text{e}$ in each case gave a pair of stereoisomers of spiro-nitrogen multicyclic systems (9b-$\text{e}$) in moderate yields, whose stereochemistry was determined by means of chemical and spectroscopic analyses. Similarly, in N-[ω-(inden-3-yl)alkyl]-phthalimides (8), spiro-nitrogen macrocycles up to 13-membered 13a-$\text{c}$ were obtained in good yields     

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)(–)-$\text{13}$).     

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 $\text{2}$.     

Ritter-reaction on steroids: Ring expansion of steroid oxethans into dihydrooxazines

The 3β-acetoxy-16β,17β-epoxymethyleneandrost-5-ene ($\text{1}$) transforms into the dihydrooxazine condensed to the sterane skeleton ($\text{4}$$\text{a}$,$\text{b}$,$\text{c}$,$\text{e}$,$\text{g}$,$\text{i}$) in a ring-expansion reaction with alkyl and aryl nitriles in the presence of HBF₄— diethyletherate The 3β-acetoxy-16α, 17α-epoxymethyleneandrost-5-ene ($\text{9}$) undergoes a Wagner-Meerwein rearrangement under similar conditions.     

Crystal structures of V3S4 and V5S8

Crystal structures of the ordered phases of V₃S₄ and V₅S₈ were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS_1.47, $\text{I2}\text{m}$ (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS_1.64, $\text{F}\text{2}\text{m}$ (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe₇S₈, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.