Reactions d'addition du tetrahydrofuranne sur les F-alkyl ethylenes,F-alkyl acetylenes et F-alkyl propynoates d'ethyle

The thermal behaviour of F-alkyl éthenes 1, F-alkyl acetylenes 2 and ethyl 3-F-alkyl propynoates 3 in tetrahydrofuran solvent was investigated. In refluxing solvent, one THF unit, reacting at its α-site, was added to the terminal unsaturated carbon of 1 and 2, and to the carbon bearing the F-alkyl group of 3; the reaction is regiospecific. Moreover, the monoadducts produced from 2 and 3 showed a strong stereoselectivity, leading respectively to E 2-(1,2-dihydryl 1-F-alkenyl)tetrahydrofurans and E ethyl 3-F-alkyl 3-(2-tetrahydrofuryl)-propenoates as the main products ($\text{cis}$-addition of THF to 2 and $\text{trans}$-addition to 3).     

Preparation of some highly halogenated derivative of furan

Direct chlorination of 2-(2H-hexafluoropropyl)-tetra- hydrofuran $\text{1}$ gave high yield of 2-(2-chlorohexafluoropropyl)- pentachloro-2,5-dihydrofuran $\text{2}$. Bromination of $\text{1}$ gave very complex mixture of products, from which three compounds, $\text{viz}$. 2-bromo-5-(2H-hexafluoropropyl)-furan $\text{3}$, 3-bromo-5-(2H-hexafluoropropyl)-furan $\text{4}$, and 2,4-dibromo-5-(2H-hexafluoropropyl)furan $\text{5}$ were isolated. Exchange fluorination of $\text{2}$ with dry KF at 240 – 300° led to a stepwise substitution of fluorines for chlorines to give mixtures of chloro-fluoro-2-(2-chlorohexafluoropropyl)-dihydrofurans $\text{7}$,$\text{8}$,$\text{9}$ and $\text{10}$, together with small amounts of 2-(2-chlorohexafluoropropyl)-3,4,5-trichlorofuran $\text{6}$.Exchange fluorination of 3,4-dihalo-2,2,5,5-tetrafluoro- 2,5-dihydrofurans $\text{11a}$ and $\text{11b}$ led to a substitution of fluorine for one vinylic halogen to give 3-halo-2,2,4,5,5-pentafluoro-2,5-dihydrofurans $\text{12a}$ and $\text{12b}$ in good yields.Compounds $\text{2}$ – $\text{12}$ were characterised by n.m.r., m.s., and i.r. spectroscopy and elemental analysis.     

Stereospecific synthesis of Z- and E-1 alkoxy-1,3-butadienes

A stereospecific, highly efficient, generally applicable synthesis of $\text{Z}$- and $\text{E}$-1-alkoxy-1,3-butadienes involving dehydrative decarboxylations of 4,5-unsaturated-2-alkoxy-3-hydroxy-carboxylic acids is described.     

Chemistry of ketene acetals II. A simple route to 2,2-dialkoxytetrahydrofurans, γ-butyrolactones, 2-(5H)-furanones and 2-alkoxy-4,5-dihydrofurans

2,2-Dialkoxytetrahydrofurans $\text{3}$ (a,b) have been synthesized from epoxides $\text{1}$ and ketene acetals $\text{2}$ using ZnCl₂ as a catalyst. By simple reactions compounds $\text{3}$ were converted into γ-butyrolactones $\text{5}$, 2-(5H)-furanones $\text{7}$ and 2-alkoxy-4,5-dihydrofurans $\text{8}$.     

Organophosphorus chemistry. Part 18. Possible intervention of a phospha-alkene in the reactions of a fluoroalkylphosphine with alkoxides

Thermal reactions of phenylphosphine with tetrafluoroethylene and 1,1-difluoroethylene give, respectively, a mixture of phenyl-1,1,2,2-tetrafluoroethylphosphine and 1,2-bis-(phenylphosphino)tetrafluoroethane, and phenyl-2,2-difluoroethylphosphine. The phenyltetrafluoroethylphosphine reacts with an excess of ethanolic or methanolic alkoxide to give the corresponding alkyl phenyl-($\text{E}$)-1-fluoro-2-alkoxyvinylphosphinite and minor amounts of the isomeric alkyl phenyl-($\text{Z}$)-2-fluoro-2-alkoxyvinylphosphinite. The use of an equimolar proportion of sodium methoxide enables the intermediate products methyl phenyl-1,2,2-trifluoroethylphosphinite and methyl phenyl-($\text{E}$)-1,2-difluorovinylphosphinite to be isolated: further reaction of these with methoxide yields the corresponding ($\text{E}$)-1-fluoro-2-methoxyvinylphosphinite. The reactions are discussed in terms of mechanisms which involve either an intermediate phospha-alkene or a hydride ion shift.     

Addition of boron enolates to isoquinolinium salts: A facile synthesis of 1-β-keto substituted 2-ethoxycarbonyl-1,2-dihydroisoquinolines and their cyclization

An efficient method to synthesize 1-β-keto substituted 2-ethoxycarbonyl (or 2-acetyl)-1,2-dihydroisoquinolines ($\text{3}$) is described, utilizing boron enolates and isoquinolinium salts. The products were treated with sodium ethoxide to afford the corresponding cyclic compounds ($\text{6}$).     

Synthesis and intramolecular cyclisation of ortho-hydroxy-2,3,3,3-tetrafluoropropiophenone. Formation of 3-fluoro-4-hydroxycoumarin

Acidic hydrolysis of 1-(o-methoxyphenyl)pentafluoropropene $\text{1}$ gave o-hydroxy-2,3,3,3-tetrafluoropropiophenone $\text{2}$ and o-methoxy-2,3,3,3-tetrafluoropropiophenone $\text{3}$. Compound $\text{2}$ when treated with aqueous potassium hydroxide or methanolic sodium methoxide gave 3-fluoro-4-hydroxycoumarin $\text{4}$. Structure of $\text{4}$ has been established by spectral means and some chemical reactions. The cyclisation mechanism of $\text{2}$ is discussed.     

The use of one-bond,heteronuclear coupling constants (1J —C,H) as structure reporters in 13 C-N.M.R. of oligosaccharides containing 3-deoxy-(=D)-manno-2-octulosonic acid

In proton-coupled, ¹³ C-n.m.r.-spectra of 3-deoxy-(=D)-$\text{manno}$-2-octulopyranosylono (KDO$\text{p}$-)derivatives, the ¹$\text{J}$-C-5,H-5 is significantly larger (148 Hz) than the respective coupling constants of the other carbon signals, and the chemical shift of the signal displaying this spacing indicates whether position 5 is glycosidated or unsubstituted.     

Fluorine-containing amino acids and their derivatives. 6. An efficient synthesis of β-fluorinated alanines via fluorohalomethylation of aminomalonates

Aminomalonates, e.g., $\text{1}$ and $\text{2}$, smoothly reacted with difluoro- and chlorofluorocarbene to produce the adducts ($\text{3}$, $\text{4}$, and $\text{5}$) in good yields. These products were successfully converted to various versatile β-fluorinated alanine derivatives, i.e., β,β-difluoroalanine ($\text{6}$), N-acyl-β-fluorodehydroalaninate ($\text{7}$), and fluoropyruvic acid ($\text{8}$).     

Base-induced intramolecular cyclisation of N-(o-azidobenzoyl)-arylamines. A new synthesis of 2-aryl-1,2-dihydro-3H-indazolin-3-ones

In strong base, e.g., sodium hydride in dimethylformamide, $\text{N}$-($\text{o}$-azidobenzoyl)arylamines cyclise in high yield to 2-aryl-1,2-dihydro-3$\text{H}$-indazolin-3-ones.     

Synthesis of the cyanohydrin of methyl perfluoroheptyl ketone and reaction of the ketone with hydrogen cyanide

The cyanohydrin of methyl perfluoroheptyl ketone $\text{2}$ was able to be synthesized by a two-step process, $\text{i.e.}$, an addition of sodium bisulfite and subsequent treatment with sodium cyanide. When equimolar amounts of ketone 2 and sodium cyanide were reacted in water or dipolar aprotic solvent such as dimethyl-formamide, acetonitrile, 1,2-dimethoxyethane and tetrahydrofuran, cyclic addition products composed of two molecules of ketone $\text{2}$ and one molecule of hydrogen cyanide were exclusively formed as 2,5-dimethyl-2,5-bis(perfluoroheptyl)-4-oxazolidone $\text{6}$ and 2,5-dimethyl-2,5-bis(perfluoroheptyl)-1,3-dioxolane-4-one $\text{7}$ instead of the cyanohydrin of ketone $\text{2}$. It is conceivable that a solubility characteristic of a compound carrying a long perfluoroalkyl group is responsible for the exclusive formation of cyclic compounds $\text{6}$ and $\text{7}$     

Hindered amines. General synthesis of α-(tert-butylamino)-isobutyramides

α-($\text{tert}$-Butylamino)-isobutyramides ($\text{1}$) can be prepared from α-haloisobutyramides ($\text{2}$) and $\text{tert}$-butylamine with sodium hydroxide in Favorskii-like reactions.     

The thiolate anion as a nucleophile Part XI. Effect of the size of the nucleophile

The nucleophilic substitution reactions of some simple fluorobenzenes, C₆H_6?xF_x with sodium methanethiolates Na⁺SR^?(R=Et, $\text{i}$-Pr, $\text{t}$-Bu) have been studied. Some fully substituted products, C₆H_6?x(SR)_x, could be obtained in DMF as solvent with R = Et and $\text{i}$-Pr, but not when R = $\text{t}$-Bu. All the new products isolated have been characterized by elemental analysis, and NMR (H-1 and F-19), infrared and mass spectroscopy.     

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.     

Regiospecific alkylation of tetronic acids : Formation of 4-alkoxy-5H-furan-2-ones and 2-alkoxy-5H-furan-4-ones

2-Alkoxy-5$\text{H}$-furan-4-ones (7,8) and 4-alkoxy-5$\text{H}$-furan-2-ones (4,5) were prepared regiospecifically and in high yields from tetronic acids (4-hydroxy-5$\text{H}$-furan-2-ones) (2) in the first case by acetylating the 4-OH group and then reacting with trialkyloxonium tetrafluoroborate, and in the second case by alkylating tetrabutylammonium tetronates with dialkyl sulfate, respectively. Direct alkylation of tetronic acids with trialkyloxonium tetrafluoroborate gave in four cases regiospecific 2-O-alkylation, in one case 4-O-alkylation and in two other cases mixtures of 2- and 4-alkoxy derivatives.     

The Stereochemistry of simple enols in solution

On the basis of their ¹H n.m.r. spectra it is concluded that vinyl alcohol and $\text{trans}$-1-propenol exist mainly in the $\text{syn}$-conformation and that $\text{cis}$-1-propenol and 2-methyl-1-propenyl exist mainly in the $\text{anti}$ conformation.     

Regiospecific cycloaddition reactions using functionalized isoprenylsilane and related compounds

1-Alkoxy-3-trimethylsilylmethyl- and 1-alkoxy-3-trimethylsilyl-l,3-butadienes ($\text{1}$) were newly prepared. The cycloaddition reactions of $\text{1}$ with various dienophiles including heterodienophiles were found to proceed very smoothly in a perfectly regiospecific mode.     

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.     

9-acetoxyanthracene derivatives. Part VIII. The mechanism of degradation of 9-acetoxy-10-arylanthracenes to anthraquinone

The mechanism of degradation of 9-acetoxy-10-arylanthracenes to anthraquinose with the use of HNO₃ in AcOH has been reported. This was proved by way of example on 9-acetoxy-10-(4′-acetoxyphenyl )anthracene (1) by means of separation and identification of intermediate products $\text{2}$, $\text{3}$ and $\text{4}$.     

Flash vacuum thermolysis of spirocyclohexadienones

In an attempt to prepare short-bridged hydroxymetacyclophanes $\text{1b-d}$, the spirocyclohexadienones $\text{2b-d}$ were pyrolyzed by flash vacuum thermolysis (FVT). Instead of $\text{1b-d}$, variable amounts of 4-(5-hexenyl)phenol ($\text{4b}$), β-hydroxybenzocycloalkenes ($\text{5b-d}$) and 4-(trans-1-alkenyl) phenols ($\text{6c-d}$) were obtained. The formation of these products is explained by invoking cleavage of a spiro bond in $\text{2}$ under formation of the intermediate diradical $\text{3}$ which, depending on the length of the aliphatic chain and on the temperature, has several pathways open for isomerization to spin-paired products.