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The Behaviour of 1,2,3-Indantrione Towards Wittig-Horner Reagents

Wittig-Horner reagents 1a,b react with 1,2,3-indantrione (2) to give the dimeric adducts 3a and 3b, respectively. Moreover, 2 reacts with tert-butyl diethyl-phosphonoacetate (1c) yielding the ethylenic compound 4. On the other hand, 2 reacts with 1d to yield the phosphonate adduct 5. Mechanisms accounting for the formation of the new products are discussed and the probable structures of the products are presented based on compatible analytical and spectral data.


Results and Discussion
We have found that the reaction of 1,2,3-indantrione (2) with 1 mol equivalent of methyl diethylphosphonoacetate (1a), in the presence of alcoholic sodium ethoxide solution, proceeds at room temperature to give a chromatographically pure adduct formulated as dimethyl 2,3-bis(3-hydroxy-1oxoinden-2-yl)butane-1,4-dioate (3a) (Scheme 1). The structure of 3a was confirmed by its satisfactory IR, 1 H-NMR and MS and elemental analyses (cf. Experimental). The 1 H-NMR spectrum of 3a showed two proton doublets centered at 4.30 and 4.33 ppm, with 3 J H-H = 16 Hz that suggested a trans configuration for the adduct [4]. Similarly, triethylphosphonoacetate (1b) reacted with 1,2,3-indantrione (2) in the presence of alcoholic sodium ethoxide solution at room temperature for 6 hours to give a crystalline product that was assigned

Scheme 2
We have also investigated the reaction of compound 2 with tert-butyl diethylphosphonoacetate (1c). The reaction of 2 with 1c was performed in alcoholic sodium ethoxide solution in 1:2 molar ratio to give the olefinic product 4 (Scheme 3). Compound 4 was obtained in a sharp-melting chromatographically pure form. Its elemental and mass spectral analyses corresponded to a molecular formula of C 21 H 24 O 6 , and the structure of the adduct was further confirmed by its IR, 1 H-NMR and mass spectral data (cf. Experimental). A possible explanation of the course of the reaction of tert-butyl diethylphosphonoacetate (1c) with 1,2,3indantrione (2) is shown in Scheme 3. In the presence of NaOEt solution trione 2 reacts with two moles of tert-butyl diethylphosphonoacetate (1c) to give the stable olefinic compound 4. Next, when 1,2,3-indantrione (2) was treated with one mole equivalent of diethyl(cyanomethyl)phosphonate (1d) in the presence of alcoholic sodium ethoxide solution at room temperature for 10 hours, adduct 5 together with some unchanged trione 2 were isolated. Carrying out the reaction using two moles of 1d instead of one led to the formation of adduct 5 in a good yield (Scheme 1). The proposed structure of compound 5 was confirmed by correct elemental analyses, molecular weight determination by MS, IR spectrum, 31 P NMR spectrum which indicates a phosphonate structure [6][7][8] and 1 H NMR spectrum.

Scheme
Apparently compound 2 reacts with one mole equivalent of diethyl (cyanomethyl)phosphonate (1d) in the presence of sodium ethoxide solution to give the unstable olefinic intermediate (B) which then reacts with another mole of 1d, in the presence of NaOEt solution, to give the stable phosphonate adduct 5 (Scheme 4).

Scheme 4
Finally, this study has been extended to include the reaction of 2 with cyanomethylenetriphenylphosphorane (Ph 3 P + --CHCN) (6) to establish whether it would behave in a similar manner.

Scheme 5
The structure of the new spiro compound 7 was established from its elemental analyses and spectral properties (cf. Experimental). Adduct 7 can be obtained via carbonyl olefination with one molecule of ylide 6 to give the reactive intermediate (B), with expulsion of triphenylphosphine oxide. Dimerization of (B) by a Diels-Alder type reaction [10], afforded the final product (Scheme 5). From the above results, it is evident that 1,2,3-indantrione (2) behaves toward cyanomethylenetriphenylphosphorane 6 in a manner quite similar to that previously reported for the reaction of 1,2,3indantrione with alkoxycarbonylmethylenetriphenylphosphoranes which produce the spiro compound 7 (R = COOCH 3 or COOC 2 H 5 ) almost exclusively (Scheme 5) [10].

Conclusions
Although 1,2,3-indantrione (2) has been reported [10] to react with resonance-stabilized Wittig reagents to give the spiro adducts 7 (R = COOCH 3  investigation, it can be concluded that the reaction of 1,2,3-indantrione (2) with Wittig-Horner reagents 1 leads to different products, depending on the nature of the phosphonate anion used as well as on the stability of the addition products [11]. The finding of the present investigation is of particular interest since it represents a novel synthetic application of Wittig-Horner reagents.

General
All melting points are uncorrected. Wittig-Horner reagents 1a-d were prepared by the Michaelis-Arbuzov reaction [12,13]. Cyanomethylenetriphenylphosphorane was prepared by a published procedure [14]. The IR spectra were measured in KBr disks with a Perkin Elmer Infracord Model 157 Grating Spectrophotometer. The 1 H-NMR spectra were run on Varian Spectrophotometer at 200 MHz, using TMS as an internal reference. The 31 P-NMR spectra were recorded in CDCl 3 (vs., 85% H 3 PO 4 as an external standard) with a JNM-PS-100Fa Spectrometer. The mass spectra were run at 70 eV with Kratos MS equipment and/or a Varian MAT 311 A Spectrometer.

Reaction of diethyl(cyanomethyl)phosphonate (1d) with 1,2,3-indantrione (2): Preparation of [1,2dicyano-2-(3-hydroxy-1-oxo-1H-inden-2-yl)-ethyl]-phosphonic acid diethyl ester (5).
A solution of two moles of sodium ethoxide in absolute ethanol was treated with equimolar amounts of phosphonate 1d and trione 2 and the resulting mixture was stirred at room temperature for 10 hr. The reaction mixture was poured onto a small amount of water, extracted with ethyl acetate and the extract was dryed over anhydrous sodium sulfate then evaporated under reduced pressure. The residual material was applied to a silica gel column chromatography using 40/60°C pet. ether -ethyl acetate (v:v) as an eluent to give 5 as pale yellow crystals in 75% yield; m.p. 176-177°C from benzene; Analysis, calcd. for C 17  To a suspension of trione 2 (0.16g, 0.001 mol) in dry benzene (25 mL), was added a solution of the ylide 6 (0.6g, 0.002 mol) in absolute benzene (25 mL). The reaction mixture was stirred at room temperature for 5 h, then evaporated under reduced pressure. The residual substance was dissolved in CH 2 Cl 2 (100 mL) and evaporated till dryness in the presence of silica gel (5 g). The reaction mixture was then added to a column previously loaded with silica gel in petroleum ether. The column was developed with petroleum ether (60/80°C) containing increasing amounts of CHCl 3 . A fraction eluted with 9:1 v/v petroleum ether/CHCl 3 gave a substance that was recrystallized from benzene to give compound 7 as colourless crystals (60% yield); m.p. 168-169°C; Anal. Calcd. for C 22 H 10  A fraction eluted by petroleum ether/CHCl 3 (7:3 v/v) yielded colourless needles, shown to be triphenylphosphine oxide by m.p., mixed m.p., and comparison of the respective IR and MS spectra.