Diaza-Wittig reaction of 4,5-disubstituted furan-2,3-diones with triphenylphosphazenes derived from 3-R-adamantanoyldiazomethane

Abstract

Reactions of 1-(3-R-adamantan-1-yl)-2-(triphenyl-λ-phosphanylidenehydrazono)ethanones with 4,5-disubstituted furan-2,3-diones gave 2-[2-(3-R-adamantan-1-yl)-5-acyl-2-oxoethylidenehydrazono]-4-Rfuran-3(2H)-ones. The diaza-Wittig reaction is very important for building up double carbon–nitrogen bonds [1–9]. A few examples of anomalous diaza-Wittig reaction involving the lactone carbonyl group in 5-arylfuran2,3-diones [10] and 1-benzofuran-2,3-dione [11] containing a ketone carbonyl group in the neighboring position have also been reported. Analogous pattern was observed in the reactions of 1-(9H-fluoren-9ylidene)-2-(triphenyl-λ-phosphanylidene)hydrazine with 5-aryl-4-benzoyl(or 3-arylquinoxalin-2-yl)furan2,3-diones [12]. In the present article we report the results of our study on the reactions of 4,5-disubstituted furan-2,3-diones IIa–IIi with 1-(3-R-adamantan1-yl)-2-(triphenyl-λ-phosphanylidenehydrazono)ethanones Ia–Ic prepared by the Staudinger reaction [13] (Scheme 1). Introduction of bulky substituents, including those containing a carbonyl group, into positions 4 and 5 of the furan ring, as well as structural modification of initial 1-acyl-2-(triphenylphosphanylidene)hydrazines Ia–Ic, was expected to not only get a deeper insight into theoretical aspects of the diazaWittig reaction but also obtain compounds possessing pharmacophoric fragments with a view to subsequent biological screening. By reaction of triphenylphosphazenes Ia–Ic with furan-2,3-diones IIa–IIi we obtained in good yields 2-[2-(3-R-adamantan-1-yl)-5-acyl-2-oxoethylidenehydrazono]-4-R-furan-3(2H)-ones IIIa–IIIl (Scheme 1). The reactions were carried out with equimolar amounts of the reactants at room temperature (method a). However, the synthesis of initial phosphazenes Ia–Ic is often accompanied by their hydrolysis during the isolation and purification procedures. In order to improve the yield of furanones IIIa–IIIl we tried to accomplish the Staudinger and diaza-Wittig reactions in a one-pot mode (method b). In this case, equimolar amounts of 3-R-adamantanoyldiazomethane IV, furandione II, and triphenylphosphine were used. Compounds IIIa–IIIl were isolated as yellow crystalline substances, which were readily soluble in DMSO, DMF, and acetone, poorly soluble in acetonitrile and diethyl ether, and insoluble in alkanes and water. The IR spectra of IIIa–IIIl contained absorption bands belonging to stretching vibrations of the ketone carbonyl group in the furan ring (C=O, 1701– 1720 cm), adamantanoyl carbonyl group (1668– 1697 cm), benzoyl carbonyl group (IIIf, IIIh, 1656– 1660 cm) , and C=C and C=N bonds (1580– 1623 cm). In the H NMR spectra of these compounds signals from protons in the adamantyl fragment were located at δ 1.65–2.82 ppm, the 4-H proton in the furan ring resonated at δ 6.17–7.03 m, a multiplet from aromatic protons was present in the region δ 6.85– 8.30 ppm, and the CH=N proton gave a singlet at δ 7.25–8.01 ppm. Compounds IIIa–IIIl are likely to be formed according to the aza-Wittig reaction mechanism [14] via attack by the phosphorus atom of phosphazene I on the lactone carbonyl oxygen atom of II to give interDOI: 10.1134/S1070428014120124