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.     

Bifunctional chiral synthons via biochemical methods. : VI. C5 isoprenoid units.

Two methods for the preparation of the isoprenoid chiron $\text{4}$ have been developed using a microbial kinetic resolution of $\text{5}$ and an enantiotopically selective hydrolysis of $\text{7}$ catalyzed by PLE.     

Highly fluorinated heterocycles. Part XII. Some reactions of the heptafluoro-p-dioxanyl anion.

2$\text{H}$-heptafluoro-$\text{p}$-dioxan has been lithiated using methyl lithium in ether and thence converted to heptafluoro-p-dioxan-2-carboxylic acid (characterised as its anilinium and S-benzylthiouronium salts and methyl ester), 2-(heptafluoro-$\text{p}$-dioxanyl)propan-2-ol [dehydrated to 2-(heptafluoro-$\text{p}$-dioxanyl)propene], heptafluoro-$\text{p}$-dioxanyltrimethylsilane, and heptafluoro-2-iodo-$\text{p}$-dioxan. This last was converted to its Grignard reagent, and to bis(heptafluoro-$\text{p}$-dioxanyl)mercury, and was copper-coupled to trans-1-chloro-2-iodoethylene.Decomposition of heptafluoro-$\text{p}$-dioxanyl-lithium gave hexafluoro-$\text{p}$-dioxene. 2$\text{H}$-heptafluoro-$\text{p}$-dioxan, with KOH and formaldehyde, afforded hexafluoro-$\text{p}$-dioxanylmethanol.     

Synthetic studies on β-lactam antibiotics. Part 16. synthesis of 1-carba-2-penem-3-carboxylic acid esters from penicillins utilizing a carbon-carbon coupling reaction

Allylazetidinones $\text{9}$, $\text{10}$, prepared by coupling of allylcoppers $\text{8}$ with chloroazetidinones $\text{6}$, $\text{7}$, were converted into carbapenem esters $\text{16}$, $\text{28}$–$\text{31}$ using an Emmons-Horner reaction to introduce the 6-side chain and an intramolecular Wittig reaction to form the carbapenem ring system.     

Electron-transfer photooxygenation. 8. dicyanoanthracene-sensitized photooxidation of ortho-dimethoxybenzene

Two cleavage products, $\text{cis,cis}$-dimethylmuconate ($\text{1}$) and $\text{trans,trans}$-dimethyl-muconate ($\text{2}$), are inefficiently produced in the 9,10-dicyanoanthracene (DCA) sensitized photooxidation of $\text{ortho}$-dimethoxybenzene ($\text{o}$-DMB) in polar solvents. An electron transfer mechanism is proposed in which superoxide ion (O^?₂0 combines with ortho-dimethoxybenzene to form a dioxetane (3), which cleaves to form ($\text{1}$). The initial products is $\text{1}$, which is rapidly converted to $\text{2}$ and other products under the conditions; $\text{no}$ cis-trans isomer is formed.     

Peri-bridged naphthalenes. 4. chalcogen-bridged acenaphthylenes

Three new electron donors, acenaphtho[5,6-$\text{cd}$]-1,2-dithiole ($\text{1}$), acenaphtho[5,6-$\text{cd}$]-1,2-diselenole ($\text{2}$), and acenaphtho[5,6-$\text{cd}$]-1,2-ditellurole ($\text{3}$), can be prepared in 28%, 22%, and 14% yields respectively by reaction of the elemental chalcogens (S, Se, Te) with 5,6-dilithioacenaphthylene ($\text{4}$). Compound $\text{4}$ is generated by treatment of 5,6-dibromoacenaphthylen ($\text{5}$), for which a convenient preparation is described, with $\text{n}$-butyllithium (2 equiv.) in THF at ?78°C.     

C-Metallated reformatsky intermediates. Structure and reactivity.

¹³C-NMR analysis of the Reformatsky intermediates from t-b$\text{u}$tyl-α-bromo acetate, t-b$\text{u}$tyl-α-bromo isobutyrate and t-b$\text{u}$tyl-α-bromo pr$\text{o}$pionate have evidenced C-metallated species. Their ability to act as n$\text{u}$cleophilic reagents under mild conditions and their selectivity towards h$\text{a}$logen-and oxygen containing electrophiles is reported.     

Athrotaxis alkaloids. Part I. Alkaloids of A. Cupressoides

Eleven homoerythrina-type alkaloids ($\text{tilda1}$-$\text{tilda9}$, $\text{tilda11}$, $\text{tilda12}$) have been isolated from A. cupressoides (Taxodiaceae), of which six ($\text{tilda6}$-$\text{tilda9}$, $\text{tilda11}$,$\text{tilda12}$) had not previously been reported.     

Cyclisierungen unter beteiligung von fluoridionen. 2. Mitteil. [1], [2]. 4.5-perfluor-1.3-dioxolane

4.5-Perfluoro-1.3-dioxolanes $\text{2}$ are available by reaction of 2(α-chloroalkoxy)perfluoro-carbonyl halides $\text{3}$ or -ketone $\text{9}$ with fluoride ions. A mechanism for the intramolecular ring- closure-reaction is proposed. Hydrogen atoms at C-2 in $\text{2}$ can be exchanged photochemically by chlorine. Starting from the 2-monochloro-derivatives $\text{16}$ the 2-monofluoro-4.5-perfluoro- 1.3-dioxolanes $\text{18}$ are formed by reaction with triethylamine- hydrofluoride.     

Adamantane rearrangement mechanisms. 1,2-trimethylenenorbornanes

Unexpected differences in the aluminium bromide-catalyzed rearrangement behaviour of 1,2-$\text{endo}$-trimethylenenorbornane ($\text{1}$) and its 1,2-$\text{exo}$-isomer ($\text{2}$) are interpreted. Isotopic labelling studies indicate that reversible abstraction of the tertiary 2-$\text{endo}$ hydride in $\text{2}$ does not occur. Instead, rearrangement to $\text{6}$ is favored. The label scrambling in the final product, adamantane ($\text{8}$), is attributed to degenerate isomerization in the proto-adamantyl precursor, $\text{7}$.     

On the stereochemistry of photoaddition between α,β-unsaturated ketones and olefins. III.

The α,β-unsaturated ketone $\text{1}$ yields with allene the photocycloadduct $\text{3}$ predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence $\text{1}$ → $\text{4}$ → $\text{5}$ → $\text{6}$ → $\text{7}$. The isomeric ketone $\text{2}$ is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked.     

An adamantane rearrangement. A new pathway

Tricyclo(4.2.2.o^1,5)decane ($\text{7}$) in the presence of AlBr₃ rearranges partly “forwards” to adamantane ($\text{1}$) and partly “backwards” to tetrahydrodicyclopentadiene ($\text{2}$, largely the oxo isomer). Intermediate $\text{14}$, characterizing the $\text{7}$→exo-$\text{8}$→$\text{14}$→$\text{3}$→$\text{1}$ forward pathway, is found only in small amounts. The detection of a new intermediate, $\text{12}$, also shows that a second major rearrangement route from $\text{7}$ to $\text{1}$ is being utilized (see dashed lines in Figure 1).     

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.     

Synthesis of 2,5-piperidinediones. regioselectivity in the dieckmann cyclization

Dieckmann cyclization of ethyl N-benzyl-N-[(ethoxycar-bonyl)methyl]succinamate ($\text{2}$) with sodium ethoxide gave regioselectively β-keto ester $\text{3}$, whereas when using potassium tert-butoxide or potassium hydride as a base the regioisomer $\text{4}$ was isolated as the main product. Transesterification of ethyl β-keto esters $\text{3}$ and $\text{4}$ with benzyl alcohol followed by hydrogenolysis and decarboxylation of the resulting benzyl esters $\text{5}$ and $\text{6}$ led to 1-benzyl- 2,5-piperidinedione ($\text{1}$). The preparation of some 4-alkyl- and 4-alkoxycarbonylalkyl derivatives was achieved by alkylation of $\text{5}$ with the appropriate halide and further hydrogenolysis.     

Synthesis of sesquiterpene antitumor lactones. 7. Studies directed toward the total synthesis of pentalenolactone. Intramolecular ene reaction.

Functionalized cyclopentene $\text{11}$ is cyclized via thermal ene reaction to $\text{12}$. All steps in the synthesis of $\text{12}$ are highly stereoselective.     

Mercury in organic chemistry. 19. Rhodium promoted methylation of organomercurials

Alkenyl-, alkynyl- and arylmercurials are methylated in excellent yield upon treatment with stoichiometric amounts of CH₃RhI₂(PPh₃)₂ ($\text{1}$). Catalytic methylation of these organomercurials is possible using $\text{1}$ and methyl iodide, but side reactions interfere.     

Cyclopropylidene formation in 7,7-dibromonorcar-3-ene oxides. Synthesis of derivatives of homobenzvalene oxide.

Treatment of $\text{4b}$, $\text{4c}$, and $\text{4d}$ with methyllithium affords $\text{5b}$, $\text{6b}$; $\text{5c}$, $\text{6c}$; and $\text{5d}$ respectively in serviceable yields $\text{via}$ carbenoid cyclization.     

Stereospecific construction of exo-tetrasubstituted olefins. The efficient synthesis of cyano-carbacyclins

Cyano-carbacyclins ($\text{2}$ and $\text{3}$) were efficiently synthesized using the stereospecific 1,4-hydrogenation of the corresponding conjugated diene $\text{10a}$ catalysed by the arene·Cr(CO)₃ complex as a key step.     

Chemistry of singlet Oxygen. XXVII. Directing effect of methoxy group in additions to methoxystyrenes

A methoxy group on a styrene double bond directs O₂ attack $\text{cis}$, giving 1,4 addition if the phenyl is $\text{cis}$, or ene reaction if a CH₃ is $\text{cis}$. If no substituent is $\text{cis}$, 1,4 attack on the $\text{trans}$ phenyl occurs at a slower rate.     

Phase equilibria for the separation of aromatic and nonaromatic compounds using mixed solvents. Part I. The system n-heptane—toluene—N-methylpyrrolidone/monoethyleneglycol

The solvent combination of N-methylpyrrolidone (NMP) and monoethyleneglycol (MEG) is used in industry for the separation of aromatics and nonaromatics (Arosolvan process).In this paper experimental results obtained for the system n-heptane—toluene—N-methylpyrrolidone/monoethyleneglycol are presented. Liquid—liquid equilibrium compositions were obtained at three different temperatures (50°C, 60°C, 70°C). For each temperature, three different solvent compositions corresponding to weight ratios of NMP/MEG equal to $\text{50}\text{50}$, $\text{62}\text{38}$ and $\text{70}\text{30}$ were considered. The different sets of experimental results obtained are correlated using the NRTL equations.Equilibrium compositions obtained using an industrial solvent mixture (NMP/MEG-$\text{58}\text{42}$) are compared with data based on the use of purified solvents.