Fluoroimines from the reaction of fluoroamino acids or fluoroketo acids with the aldehyde or amine form of vitamin B6: Part III. Influence of fluorine on the formation and the reactivity of fluoroimines derived from β-fluoroaspartates or β-fluorooxaloacetate

The introduction of fluorine at the β-position in aspartate and in oxaloacetate, the typical amino acid-keto acid couple in transamination, induces large effects in their reaction with respectively pyridoxal 5′-phosphate (PLP) ($\text{1}$) and pyridoxamine 5′-phosphate (PMP) ($\text{4}$). The formation of imine intermediates through reaction of $\text{1}$ with $\text{erythro}$ or $\text{threo}$-β-fluoroaspartate ($\text{2e}$ and $\text{2t}$) and through reaction of $\text{4}$ with β-fluorooxaloacetate $\text{5}$ is highly favored in comparison with that of non-fluoro compounds. The stereoisomers of the imines are unambiguously determined using a reduction reaction. The evolution of these intermediates shows that no transaminatlon is observed and that a dehydrofluorination occurs suggesting that the β-fluoro moiety in the intermediate turns into a good leaving group, changing the model reaction of transamination on α carbon through the aldimine-ketimine tautomerization to an elimination on β carbon.     

Synthesis of 4a-, 4e-phenyladamantanones and 2,4-o-benzenoadamantane by π-route

The acid catalysed reaction of 4-oxa-homoadamantan-5-one ($\text{1}$) with benzene yielded a mixture of 4^a-phenyladamantan-2-one ($\text{7}$), the equatorial isomer' ($\text{8}$) and 2-phenyl-2,4-o- benzenoadamantane ($\text{9}$) A plausible reaction pathway for the occurrence of $\text{9}$. is put forward. The structure of $\text{9}$, was deduced from spectroscopic data and reaction of the proposed intermediate 2,4^a-diphenyladamantan-2-ol ($\text{11}$) with acid. 2,4-o-Ben-zenoadamantane ($\text{16}$) is prepared likewise.     

Photochemistry of 4-pyrimidinones in aqueous solution. Isolation of reversible photohydrates

Both the irradiation of 4-pyrimidinones ($\text{la-c}$) and the reaction of the isolated Dewar 4-pyrimidinones ($\text{2a-c}$) in aqueous solution gave the corresponding photohydrates ($\text{3a-c}$) which reverted spontaneously to the starting $\text{la-c}$ in the dark reaction. The photohydrates were isolated in crystalline form and their physical properties were determined.     

The synthesis of cis- and trans-1,2-dibromocyclopropane

A preparative route to cis- and trans-1,2-dibromocyclopropane ($\text{1}$) was developed via the Hunsdiecker reaction of silver cyclopropane-1,2-dicarboxylate ($\text{2}$). Cis- and trans-$\text{2}$ gave the same ratio of cis- and trans-$\text{1}$ (1:3.2). The mechanism of this reaction is briefly discussed.     

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.     

An electrochemical chlorinative ene-type reaction of isoprenoids

The chlorinative ene-type reaction of isoprenoids ( $\text{1}$ → $\text{2}$ ) has been performed by electrolysis in CH₂Cl₂-H₂O-NaCl system. The reaction provides useful allylic chlorides $\text{2}$ for terpene synthesis in high yields and is affected strikingly by the nature of halide ions and solvents. dl-Theaspirane $\text{2}$$\text{1}$ was prepared from α-dihydroionol $\text{via}$ the electrolysis.     

Transition structures for the reaction of difluorocarbene with propene

Two $\text{ab}$$\text{initio}$ transition structures for the reaction of difluorocarbene with propene have been located with gradient techniques and the 3-21G basis set. The activation energy is 1.3 kcal/mol lower than for the reaction with ethylene. Two transition structures with the fluorines approaching $\text{syn}$ or $\text{anti}$ to the methyl group are identical in energy     

Photodecomposition of selenosulfonates and their facile photoaddition to alkenes 1

Phenyl areneselenosulfonates ($\text{1}$) are very photosensitive and easily undergo photodecomposition via initial homolysis of the SeS bond. In the presence alkenes this facile photodissociation of $\text{1}$ can be used to initiate a free radical chain reaction (eq 6) that leads to addition of $\text{1}$ to the alkene to form β-phenylselenosulfones ($\text{2}$). The photoaddition requires much shorter reaction times than the non-photolytic addition of $\text{1}$ to alkenes described recently.²     

The facile (<−50°C) formation of cis-bicyclo[6.1.0]nona-2,4,6-trienes from cyclonona-1,3,5,7-tetraenes: A symmetry - forbidden reaction

The formation of the $\text{cis}$-bicyclo [6.1.0] nona-2,4,6-trienes $\text{4a}$-$\text{c}$ is not due to the sequence $\text{1}$ → $\text{2}$ → $\text{4}$, which would involve the symmetry-forbidden reaction $\text{2}$ → $\text{4}$ even at ?50°C. Rather, reaction of RX at C^4–7 of $\text{5}$, which is formed together with $\text{1}$, leads (probably via $\text{6a}$-$\text{c}$ and $\text{7a}$-$\text{c}$ to $\text{4a}$-$\text{c}$.     

Monitored aminolysis of 3-acylthiazolidine-2-thione : A new convenient synthesis of amide

3-Acylthiazolidine-2-thiones ($\text{1}$) were easily prepared and they were treated with several amines in dichloromethane to give amides $\text{4}$ in very high yields within a short time. Aminoalcohols and aminophenols were selectively converted into acylaminoalcohols and acylaminophenols, respectively, by this reaction. One can monitor the reaction by disappearance of the yellow color of the starting material $\text{1}$. Some amide alkaloids ($\text{1}$$\text{5}$–$\text{1}$$\text{8}$) have effectively been synthesized.     

Acid-catalyzed cyclizations of n-vinyl-α-sulfinylacetamides A novel synthetic approach to erythrinane

Under the Pummerer reaction conditions, N-(1-cyclohexenyl)-N-methyl-α-(methylsulfinyl)acetamide ($\text{7a}$) cyclized in a 5-endo trigonal fashion through the intermediary cation ($\text{8}$) to give the tetrahydro-4H-oxindole ($\text{10}$). The reaction was successively applied to a novel synthesis of erythrinane skeleton.     

5,12-dihydro-6,11-didehydronaphthacene,A derivative of 1,4-didehydronaphthalene

Treatment of the di-lithium derivative of 1,2-diethynyl-benzene ($\text{1}$) with $\text{o}$-xylene-α,α′-diol di-$\text{p}$-toluenesulphonate ($\text{2}$) in tetrahydrofuran led to 5,12-dihydronapthacene ($\text{5}$) as the only identifiable product. This reaction presumably involves 5,12-dihydro-6,11-didehydronaphthacene ($\text{4}$) as an intermediate, and this was confirmed by the formation of 5,12-dihydro-6,11-dideuterio-naphthacene when the reaction was carried out in tetrahydrofuran-$\text{d}$₈.     

Potooxygenation of nitroaromatic compounds. Catalytic effects in the reaction of molecular oxygen with nitrobenzyl derivatives.

The photooxygenation reaction of several nitroaromatic compounds ($\text{1}$ - $\text{8}$) in aqueous solution is described, the mechanism of reaction is believed to involve photogenerated nitrobenzyl carbanions.     

A facile formation of cyclic selenuranes and a cyclic selenurane oxide in the reaction of 2-methylseleno- and 2-phenylselenobenzoic acids and their derivatives with t-butyl hydroperoxide

The reaction of 2-methylselenobenzoic acid with 1,1′-carbonyldiimidazole followed by addition of t-butyl hydroperoxide gave cyclic selenuranes $\text{2a}$ and $\text{3a}$, suggesting the intramolecular insertion of the neighboring selenium atom into the OO bond of t-butyl 2-methylselenoperoxybenzoate. In the reaction of 2-phenylselenobenzoyl chloride with t-butyl hydroperoxide, cyclic selenurane $\text{2b}$ and the oxide $\text{7}$ were obtained.     

Inept-29Si NMR study of a TiCl4-mediated reaction of an enol silyl ether

Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene ($\text{1}$) and 2-phenyl-2,2-dimethoxyethanal ($\text{2}$) under TiCl₄ condition gave the γ-hydroxycyclopentenone product $\text{3}$. The reaction was followed by INEPT²⁹Si NMR. Implication to the mechanism of the reaction was discussed.     

Alpha-lithiosilanes: III. The Reaction of Vinylalkoxysilanes with Organolithium Reagents

The reaction of two equivalents of vinyldimethylethoxysilane or vinyldimethylmethoxysilane with hydrocarbon soluble alkyllithium reagents; $\text{t}$-BuLi, $\text{s}$-BuLi, or $\text{n}$-BuLi; in hexane at low temperature gives high yields of 1,1-dimethyl-2-alkyl-4-(dimethylalkoxysilyl)silacyclobutanes. With methyl- or phenyllithium substituted vinylsilanes are obtained. The stereochemistry of the silacyclobutanes is assigned on the basis of Si-29 and H-1 NMR. For vinyldimethylethoxysilane the ratio of cis to trans silacyclobutane is about $\text{57}\text{43}$, and is independent of the alkyllithium reagent used. In the reaction of vinyldimethylmethoxysilane with $\text{t}$-BuLi a $\text{sol70}\text{30}$ ratio of the cis and trans silacyclobutane is obtained. A pathway is proposed which is consistent with the stereochemical results and with the products isolated in the reaction run in THF.     

A high yield synthesis of (±)-5,8-dimethoxy-2-α-hydroxyethyl-3,4-dihydronaphthalene,a key intermediate in anthracyclinone synthesis

The dimethoxytetralol ($\text{2}$) gives on Vilsmeier reaction the dihydronaphthaldehyde ($\text{3}$) (yield,92%), which on Grignard reaction with MeMgI affords the title compound ($\text{6}$) (yield,~100%), the reactions constituting a high yield synthesis of this important anthracyclinone intermediate.     

Studies on the reaction of 1,2-dicarbonyl compounds with dimethyl 3-ketoglutarate. Steric and electronic effects

The steric and electronic influences of substituents attached to the 1,2-dicarbonyl system on the success of the reaction of 1,2- diketones with dimethyl 3-ketoglutarate $\text{2}$ have been examined. It is clear from the reaction of $\text{2}$ with benzil, thienil, furil, and phenanthrenequinone $\text{5}$, respectively, coupled with ¹³C NMR spectroscopy of the reaction intermediates, that steric effects play a major role in the overall success of the reaction to provide $\text{4}$. This is analogous to the situation observed earlier with 1,2-diketones, R-CO-CO-R, where R represented an aliptiatic or alicyclic group.     

Enantioselective synthesis of β-hydroxyisobutyric acid: a useful synthon in the synthesis of polypropionate-type natural products

The aldol reaction of formaldehyde with the dicyclopentylborinyl enolate derived from $\text{S}$-(or $\text{R}$-) 1-tert-butyldimethylsilyloxy-l-cyclohexylbutan-2-one, followed by desilylation and sodium meta-periodate oxidation, provides $\text{R}$-(or $\text{S}$-) β-hydroxyisobutyric acid.     

Chemoselective protection of heteroaromatic aldehydes as imidazolidine derivatives : Preparation of 5-substituted furan- and thiophene-2-carboxaldehydes via metallo-imidazolidine intermediates

Furan-, thiophene- and $\text{N}$-methylpyrrole-2-carboxaldehydes may be transformed into the corresponding $\text{N}$,$\text{N}$'-dimethylimidazolidines in a reaction not requiring acid catalysis. The resulting furan and thiophene (but not $\text{N}$-methylpyrrole) derivatives may be metallated in high yields [predominantly at the 5 (α-) positions of the heteroaromatic rings] and the carboxaldehyde functionality regenerated under very mild conditions. Treatment of the aldehydoketone 2-acetyl-5-formylthiophene with $\text{N}$,$\text{N}$'-dimethylethylenediamine gives $\text{only}$ the product of reaction at the aldehyde function thus establishing this methodology as a potentially valuable method for the protection of an aldehyde in the presence of a ketone.