Synthesis of ethyl 4,5-bis(diethoxyphosphorylmethyl)-3-furoate

Preparative procedure for 4,5-bis(diethoxyphosphorylmethyl)-3-furoate from 4-chloromethyl-3-furoate is developed. It includes substitution of chlorine with iodine, phosphorylation by means of the Arbuzov reaction, chloromethylation of 4-(diethoxyphosphorylmethyl)-3-furoate in the position 5 of the furan ring, substitution of chlorine with iodine in the obtained chloromethyl derivative, and repeated phosphorylation with triethyl phosphite. It was found that ethyl 4-(diethoxyphosphorylmethyl)-5(chloromethyl)-3-furoate reacts with sodium diethyl phosphite by two pathways. Besides usual nucleophilic substitution leading to phosphonate, transfer of the reaction center in the position 2 of the furan ring takes place. The ambident diethylphosphite anion in this case reacts at the oxygen to give tertiary phosphite. The latter is oxidized with the air oxygen to form ethyl 2-(diethoxyphosphoryloxy)-4-(diethoxyphosphorylmethyl)-5-methyl-3-furoate. Unlike that analogous iodomethyl phosphonate is phosphorylated selectively under the conditions of the Arbuzov reaction.     

Furoyl phosphonates

A series of furoyl phosphonates bearing methyl, methoxymethyl, and diethoxyphosphorylmethyl groups in the furan ring have been synthesized via the Arbuzov reaction from the corresponding acid chlorides. NMR spectral parameters of the prepared compounds were studied. The values of coupling constants between the phosphorus nuclei and the carbon nuclei of the furan ring have been examined with relation to the location of the acylphosphoryl group in the furan ring, the nature of second substituent, and location of the latter with respect to the phosphorus-containing substituent in the furan ring. The substitution in position 4 of the furan ring of 3-furoyl phosphonates has been shown to strongly decrease the value of the coupling constant between the phosphorus nucleus and the C² atom of the heterocycle. The interaction between the phosphorus nuclei has not been detected in the spectra of the compounds containing both diethoxyphosphorylmethyl and acylphosphonate fragments.     

Synthesis of isomeric bromo(diethoxyphosphorylmethyl)furans

Series of the previously unknown bromo(diethoxyphosphorylmethyl)furans including four of six possible regioisomers is synthesized. The target products were obtained by bromination of the corresponding (diethoxyphosphorylmethyl)furans or by a four-step synthesis including bromination of isomeric methyl-furancarboxylates, reduction of the products formed to the corresponding alcohols, substitution of hydroxy group with halogen and phosphorylation by the Michaelis-Becker reaction. It was established for the first fime that in the course of bromination of alkyl carboxylates and phosphonates of the furan series under the typical conditions of electrophilic reaction (Br₂ + 10% molar of AlCl₃, chloroform) the substituent enters not only into the heteroring, but also into the side chain. In the case of 5-methyl-2-(diethoxyphosphorylmethyl)furan only the last reaction pathway is observed. It is shown that bromo(chloromethyl)furans react with sodium diethyl phosphite not only according to the Michaelis-Becker scheme leading to phosphonates, but also by the pathway of debromination of the furan ring. The last unexpected reaction may acquire a practical use for removing a substituent protecting the α-position of the furan ring under mild conditions.     

Aminomethylation of 2- and 3-(Diethoxyphosphorylmethyl)furans

Dimethyl(methylene)ammonium chloride reacts with 2-, 3-(diethoxyphosphorylmethyl)furansby the free position of the furan ring to give the corresponding aminomethyl derivatives. 2,5-Disubstitutedfurans do not enter this reaction.     

Synthesis of 3-(furyl)acrylates containing several phosphonate groups

Isomeric (diethoxyphosphorylmethyl)furoyl phosphonates react with ethoxycarbonylmethylenetriphenylphosphorane to form 3-[(diethoxyphosphorylmethyl)fyryl]-3-(diethoxyphosphoryl)acrylates with trans-location of phosphonate and ester groups regardless of the structure of heterocyclic residue. 2,5-Bis(diethoxyphosphorylmethyl)-3-furoyl phosphonate and 4,5-bis(diethoxyphosphorylmethyl)-2-furoyl phosphonate prepared from the corresponding acid chlorides via the Arbuzov reaction behave analogously. The dependence of coupling costants J _PP and J _PC on the location of phosphorus-containing substituents in the furan ring of these compounds is analyzed.     

Synthesis of phosphorylated derivatives of furoylglycine and furoyl-β-alanine

Chloromethylfuroyl chlorides react with alkyl glycinates and β-alanates to form the corresponding chloromethylfuroyl amides. The compounds obtained are phosphorylated with triethyl phosphite under the conditions of the Arbuzov reaction to give (diethoxyphosphorylmethylfuroyl amides. Alkaline hydrolysis of these compounds proceeds only at the carboxy group leading to (diethoxyphosphorylmethyl)furoylglycine and furoyl-β-alanine. Selectivity of hydrolysis does not depend on the position of carboxamide and diethoxyphosphorylmethyl groups in the furan ring.     

Addition of butanethiol to alkyl 3-furyl-3-(diethoxyphosphoryl)acrylates

By an example of butanethiol the addition of mercaptanes in the presence of bases to alkyl 3-furyl-3-(diethoxyphosphoryl)acrylic acids having methyl, methoxymethyl, or diethoxyphosphorylmethyl substituent in the furan ring was studied. It was shown that in the majority of cases alkyl 2-(butylthio)propionate was the main product, and 3-(butylthio)propionate was the minor one. Ethyl 3-(4-methylfur-3-yl)-3-(diethoxyphosphoryl) acrylate affords these two substances in equal quantities. In the case of ethyl 3-(4-methoxymethyl-5-methylfur-2-yl)-3-(diethoxyphosphoryl)acrylate only 3-(butylthio)propionate is formed.     

Synthesis of 1-functionalyzed 3-(diethoxyphosphorylmethyl)-4,5,6,7-tetrahydrobenzo[<Emphasis Type="Italic">c</Emphasis>]furans

A series of 3-(diethoxyphosphorylmethyl)-4,5,6,7-tetrahydrobenzo[c]furans functionalized in the position 1 including the unsubstituted phosphonate, diethylaminomethyl derivative, carboxylic acid, its ester, chloride, amide, and nitrile was synthesized. For the first time in the furan series decarboxylation of PO-ester of phosphonocarboxylic acid was carried out. Some specific features of behavior of the derivatives of 4,5,6,7-tetrahydrobenzo[c]furan in the reactions with thionyl chloride, phosphorus pentachloride, ammonia, and N-bromosuccinimide unusual for common alkylfurans were found.     

Synthesis of phosphonomethylated acid chlorides,alcohols, and aldehydes of the furan series

Diethoxyphosphorylmethyl derivatives of furancarboxylic acids react with thionyl chloride in the presence of DMF to form the corresponding acid chlorides. Compounds synthesized were reduced with sodium borohydride in the DMF-dioxane medium to give hydroxymethyl compounds. Obtained phosphorylated alcohols were oxidized to aldehydes by chromium trioxide-pyridine complex in methylene chloride. The diethoxyphosphorylmethyl group remains untouched in all these transformations. A series of phosphorylated acid chlorides, alcohols, and aldehydes including all six versions of mutual location of phosphorus-containing substituent and another functional group in the furan ring was synthesized. It is established that 2,3- and 3,2-(diethoxyphosphorylmethyl)(chlorocarbonyl)furans in the course of vacuum distillation undergo cyclization to 4,5(2,3-furo)- and 4,5(3,2-furo)-1,2-oxaphosphorines.     

3-Chloroalkylfurans in the reaction with sodium diethyl phosphite

Reduction of 3-acylfurans with lithium alumohydride in ether yields stable secondary alcohols. By treatment with thionyl chloride in the presence of pyridine, they are converted to the corresponding chlorides. 3-(1-Chloroethyl)furan and 5-methyl-3-(1-chloroethyl)furan react with sodium diethyl phosphite to give two products: 3-(1-diethoxyphosphorylethyl)furans and 3-ethyl-2-(diethoxyphosphoryloxy)furans. The methyl group in position 5 of the furan ring increases the relative phosphate content of the mixture by a factor of approximately 2.5. Blocking of position 2 or both positions 2 and 5 of the ring with methyl groups leads to phosphoate formation only. The reaction of 2,5-dimethyl-3-(1-chloro-2-methylpropyl)furan also occurs according to the Michaelis-Becker scheme. The products of the side chain dehydrohalogenation with sodium diethyl phosphite were not found.     

2,3- and 3,4-Bis(diethoxyphosphorylmethyl)-5-tert-butylfurans

Reduction of 2-, 4-acetoxymethyl derivatives of 5-tert-butylfuran-3-carboxylic acid leads to the corresponding bis(hydroxymethyl)furans. Bis(chloromethyl)furans prepared from the latter were involvedin reaction with sodium diethyl phosphite. In the presence of two equivalents of a phosphorus-containing nucleophile, bis(phosphonomethyl)furans are formed. One equivalent of sodium diethyl phosphite reacts with 3,4-bis(chloromethyl)furan to give a mixture of 3-and 4-phosphorylated products in a 4.5:1 ratio in a low yield. The revealed difference in reactivity between the 3- and 4-chloromethyl groups demonstrates the importance of shielding of the chloromethyl group by the neighboring tert-butyl substituent. Examination of the ¹H NMR spectra of 3,4-bis(hydroxymethyl)-, 3,4-bis(chloromethyl)-, 3,4-bis(diethoxyphosphorylmethyl)-5-tert-butylfurans, and also specially prepared 5-tert-butyl-3-(diethoxyphosphorylmethyl)-4-(ethoxymethyl)-2-methylfuran established that the signal of the substituent neighboring to the tert-butyl group is always shifted downfield.     

Furan ring opening–indole ring closure: SnCl2-induced reductive transformation of difuryl(2-nitroaryl)methanes into 2-(2-acylvinyl)indoles

A simple and efficient method for the synthesis of 2-(2-acylvinyl)-3-(5-alkyl-2-furyl)indoles by reductive recyclization of bis(5-alkyl-2-furyl)(2-nitroaryl)methanes is reported. This transformation was carried out by heating the substrates with SnCl₂·2H₂O in ethanol. The intermediate nitrosoarene moiety interacted with the furan ring via electrophilic nitrogen attack onto the C(2) position of the furan ring. It was shown that the related bis(5-alkyl-2-thienyl)(2-nitroaryl)methanes under the same reaction conditions failed to undergo the analogous recyclization and were transformed into bis(5-alkyl-2-thienyl)(2-aminoaryl)methanes.     

Synthesis of 3,4-Disubstituted Phosphorus-containing Furans with Free 2 and 5 Positions

A synthetic approach to -(chloromethyl)furans with free 2, 5 positions is developed. It isshown that these compounds enter the Michaelis-Becker reaction to form usual phosphorylation products.With 3,4-bis(diethoxyphosphorylmethyl)furan, two conformers with different chemical shifts of phosphorus nuclei and PCH₂ protons were detected.     

Synthesis of Alkyl 2-Bromomethyl-4-(diethoxyphosphorylmethyl)-5-tert-butylfuran-3-carboxylates and Their Reactions with Nucleophilic Agents

Alkyl 2-methyl-4-(diethoxyphosphorylmethyl)-5-tert-butylfuran-3-carboxylates are selectivelybrominated with N-bromosuccinimide at the methyl group in position 2 of the ring. The resulting bromo-methyl derivatives react with secondary amines to form tertiary amines, with sodium butylthiolate inmethanol to form the corresponding sulfide. The reaction with potassium thiocyanate in DMF at 80°C givesa mixture of thiocyanate and isothiocyanate. When treated with phenolate or alcoholate ions, the bromomethylfurans decompose.     

Nitration of 2- and 4-[2-(2-furyl)vinyl]thiazole derivatives

Nitration of 4-methyl-2-[2-(nitro-2-furyl)vinyl]thiazole with a mixture of concentrated nitric and sulfuric acids leads to 4-methyl-5-nitro-2-[2-(3,5-dinitro-2-furyl)vinyl]thiazole. Under the same conditions 2-methyl- and 2-acetamido-4-[1-R-2-(5-nitro-2-furyl)vinyl]thiazoles (R=CH₃, Cl) are nitrated in the 3 position of the furan ring, 2-amino-4-[1-chloro-2-(5-nitro-2-furyl)vinyl]thiazole is nitrated in the 5 position of the thiazole ring and 2-acetamido-5-nitro-4-[2-(2-furyl)vinyl]thiazole undergoes profound changes. Under the influence of a mixture of of nitric acid and acetic anhydride the latter compound is converted quantitatively to the 5-nitro derivative (with respect to the furan ring), whereas 4-[2-(5-nitro-2-furyl)vinyl]thiazole derivatives do not undergo reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 314–317, March, 1977.     

Synthesis and some transformations of 2-(2-furyl)naphtho[1,2-<Emphasis Type="Italic">d</Emphasis>]oxazole

By condensation of 1-amino-2-hydroxynaphthalene with furoyl chloride in 1-methyl-2-pyrrolidone 2-(2-furyl)naphtho[1,2-d]oxazole was synthesized and brought into electrophylic substitution reactions: nitration, bromination, sulfonation, formylation, and acylation. The substituent commonly was introduced into the position 5 of the furan ring, but at the nitration and bromination electrophilic attack was directed both at the furan ring and the naphthalene fragment.     

Different specificities in the bromination of 6-(2-furyl)imidazo[2,1-b]thiazole and its derivatives with 1 mole of bromine

The action of 1 mole of bromine on 6-(2′-furyl)imidazo[2,1-b]thiazole, its 2-methyl-, 3-methyl-, and 2,3-dimethyl-substituted derivatives, and their hydrobromides in chloroform and glacial acetic acid was studied. The bromination of bases containing a methyl group in the 3 position leads primarily to the 5′-derivatives with respect to the furan ring in chloroform, whereas in the remaining cases 5-bromo derivatives with respect to the imidazothiazole system are formed. Compounds of the latter type are formed by the action of bromine in glacial acetic acid or of sodium hypobromite in alkaline media on the bases. The hydrobromides are brominated in both acetic acid and chloroform, regardless of the substituents in the thiazole ring, primarily in the 5′ position of the furan ring. The structures of the bromination products were proved by means of alternative syntheses, thin-layer chromatography, and the PMR spectra.     

2-Substituted imidazoles. 3. Metallation of 1-methyl-2-phenyl- and 1-methyl-2-(furyl-2)imidazoles

1-Methyl-2-phenylimidazole reacts with butyllithium to give 5-lithium substituted products. On the other hand, 1-methyl-2-(furyl-2)imidazole is metallated under the same conditions exclusively on the furan ring and primarily in the 3 position. The introduction of triethylamine into the reaction mixture, or replacement of butyllithium by lithium 2,2,6,6-tetramethylpiperidide leads to the formation of a lithium derivative substituted at the 5-position of the furan ring exclusively.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 61–66, January, 1992.     

Synthesis of 2-substituted 3,4-bis(diethoxyphosphorylmethyl)furans

Bromination of ethyl 4-(diethoxyphosphorylmethyl)-5-methylfuran-2-carboxylate and 4-(diethoxyphosphorylmethyl)-5-methylfuran-2-carbonitrile with N-bromosuccinimide followed by phosphorylation via the Arbuzov reaction have yielded the corresponding 2-substituted 4,5-bis(diethoxyphosphorylmethyl)furans. Synthesis and transformations of bisphosphorylated 2-furoic acid and its derivatives are described.

     

Synthesis and some transformations of new 9-furylnaphtho[2,3-b]furan derivatives

The synthesis of a number of naphtho[2,3-b]furan derivatives, containing a furyl substituent in position 9 by intramolecular cyclization of 2-carboxy and 2-formylbis(5-alkylfur-2-yl)methanes is described. The reactivity of the title compounds in formylation, acetylation, nitration, and oxidation reactions has been investigated. It was shown that nitration of 2-methyl-9-(5-methyl-2-furyl)naphtho[2,3-b]furan-4-yl acetate leads to oxidative furan ring opening rather than to electrophilic substitution.