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Synthesis and Selected Reactions of 4(5)-Functionalized 2(3)-Furoyl Phosphonates
Abstract
Approaches to the synthesis of a wide range of phosphorylated derivatives of 3-(furyl)acrylic acid and 4-(furyl)buten-2-one with various functional groups in the furan ring have been developed.
Reactions of 2-and 3-furoyl chlorides having chloromethyl or butylthiomethyl group in the adjacent position of the furan ring as well as of analogous N-morpholinomethylfuroyl chloride hydrochlorides with triethyl phosphite have been studied. The synthesized chloromethylfuroyl phosphonates have given the corresponding products of nucleophilic substitution in the reactions with sodium azide and potassium thiocyanate in the case of 4-chloromethyl-3-furoyl phosphonate. In the reaction of 3-chloromethyl-2-furoyl phosphonate with sodium azide, cleavage of the P-C bond takes place simultaneously with nucleophilic substitution. Potassium thiocyanate forms 3-thiocyanatomethyl-2-furoyl phosphonate in the reaction with this substance. The synthesized stable furoyl phosphonates enter the Wittig reaction with resonance-stabilized phosphoranes to give phosphorylated furylalkenes. If these compounds carry a chloromethyl group in the furan ring, they react with sodium azide and potassium thiocyanate to give the corresponding products of nucleophilic substitution. Analogously, aminomethyl derivatives have been obtained in the reaction with morpholine at room temperature.
5-Chloromethyl-2-furoyl chloride when treated with triethyl phosphite has given 5-chloromethyl-2-furoyl phosphonate. This compound has reacted with sodium azide in the presence of potassium iodide to give 5-azidomethyl-2-furoyl phosphonate. Treatment of 5-chloromethyl-2-furoyl phosphonate with secondary amines even under mild conditions has caused cleavage of P–C bond with liberation of diethyl hydrogen phosphite and formation of 5-chloromethyl-2-furancarboxamide. Butanthiol in the presence of potassium carbonate in acetonitrile has converted the chloromethyl group into the butylthiomethyl one and simultaneously split the P–C bond with the formation of the corresponding thioester. Under the action of S-methylthiuronium iodide and triethylamine, 5-chloromethyl-2-furoyl phosphonate has been unexpectedly reduced into the 5-methyl derivative. 5-Butylthiomethyl- and 4-(N-morpholinomethyl)-2-furoul chlorides have been phosphorylated with triethyl phosphite into the corresponding 5-functionalized 2-furoyl phosphonates. The prepared furoyl phosphonates have reacted with resonance-stabilized phosphoranes to give phosphorylated derivatives of 3-(furyl)acrylates and 4-(furyl)but-3-en-2-one with trans-location of phosphoryl and carbonyl groups with respect to the double bond.
Addition of diethyl- and diisopropyl hydrogen phosphites to isomeric (methoxycarbonyl)-2- and 3-furaldehydes in the presence of sodium ethylate or potassium fluoride led to the formation of the corresponding hydroxyphosphonates. When treated with DMSO-acetic anhydride mixture at room temperature these compounds were selectively oxidized to the corresponding furoyl phosphonates. 2-Methoxycarbonyl-3- furoyl phosphonate was synthesized via the Arbuzov reaction from 2-methoxycarbonyl-3-furoyl chloride and triethyl phosphite. The obtained isomeric (methoxycarbonyl)furoylphosphonates regardless of the structure of heterocyclic fragment react with ethoxycarbonylmethylenetriphenylphosphorane to give ethyl 3-(furyl)-3-(dialkoxyphosphoryl) acrylates with trans-location of phosphoryl and carbonyl groups against the double bond.
Reaction of chloromethyl derivatives of ethyl 3-furyl-3(diethoxyphosphoryl)acrylates with sodium azide in acetonitrile in the presence of catalytic amount of potassium iodide proceeds with substitution of halogen with the azido group. The same chloromethyl derivatives react with potassium thiocyanate under analogous conditions to give a mixture of thiocyanates and isothiocyanates in (0.6–0.8) : 1 ratio save the case of ethyl 3-(3-chloromethylfur-2-yl)- and 3-(4-chloromethylfur-3-yl)acrylates when only thiocyanates are formed. Bromination of diethyl 5-methyl-2-furoyl phosphonate with N-bromosuccinimide afforded 5-bromomethyl-2-furoyl phosphonate. In the reaction with potassium thiocyanate it forms only thiocyanate.
Methoxymetyl derivatives of furoylphosphonates react with ethoxymethylenetriphenylphosphoranes to give phosphorylated (methoxymethylfuryl)acrylates. The reaction proceeds stereoselectively: phosphoryl and ester groups at the double bond are always trans-located. Treatment with dichloromethylmethyl ether and catalytic amount of zinc chloride converts the methoxymethyl group in the synthesized compounds into chloromethyl one. The ester group and the double bond are inert under these conditions.
AbstractA new synthetic approach to vinylphosphonates is presented. The reaction of diethyl benzoylphosphonate (1) with diethyl methoxycarbonyl‐methyl‐phosphonate (2) gives diethyl 2‐methoxycarbonyl‐l‐styrylphosphonate (3) as a mixture of geometrical isomers (Z‐3) and (E‐3) in the ratio of 83:17. In contrast, reaction of 1 with the heterocyclic phosphonate reagent, 2‐methoxycarbonyl‐methyl‐2‐oxo‐4,5‐dimethyl [1,3,2] dioxaphospholane (4) leads to a mixture of the isomers (Z‐3) and (E‐3) in the ratio of 20:80.