Synthesis and Spectral Characterization of Novel Spiroindan-1 , 3-Dione : A Diels Alder Adduct

DMSO/Ac 2 O reagent converts 1,3-indandione (1) to an unusual dimer 1H,1H-2,2-biindene-1,1,3,3(2H,2H) tetrone and a dimeric condensation product along with an ylide (1a) at room temperature.This reagent also brings about oxidation of secondary alcohols to corresponding ketones, methyl thiomethylation, and N-hydroxymethylation in phthalimide and converts 4-hydroxycoumarins and dicoumarol to different oxidative and degradation products under varying conditions. However, when 1,3-indandione was refluxed with DMSO/Ac 2 O reagent at 150C, it afforded a novel compound, 2-spiroindan 1,3-dione (2), a Diels Alder Adduct, analogous to (3) obtained upon treatment of 1,3-indandione with formaldehyde in presence of primary amines.


Introduction
Dimethyl sulphoxide, a polar aprotic liquid, has been used in combination with a number of activators but the most important and extensively used was acetic anhydride.DMSO-acetic anhydride reagent has been a subject of monographs.It brings about oxidative rearrangements [1], oxidative degradation, oxidation of secondary alcohols [2], and methyl thiomethylates -OH group in different sugar units [3].Interaction of this reagent with 4-hydroxy coumarins and 3-substituted 4hydroxy coumarins results in a wide range of products under varying conditions both of mechanistic and pharmacological interests [4].
Keeping in view it was thought better to interact 1,3indandione with DMSO-acetic anhydride reagent at elevated temperature (∼150 ∘ C) as the former contains active hydrogens which can protonate the oxygen of DMSO and set the reaction in motion.procedure [14].All reactions were monitored by TLC plates precoated with Silica gel Si 60 F 254 from Merck.Melting points were recorded on Tempo block melting point apparatus and are uncorrected.IR spectra were recorded on Perkin Elmer spectrophotometer of the range 4000-400 cm −1 . 1 HNMR was recorded on 300 MHz Bruker instrument.Mass was recorded on Jeol mass spectrometer in electron ionization mode.Ylide (1a) was synthesized by the earlier reported method [15].

2-Spiroindan-1,3-Dione.
A mixture of 1,3-indandione (1 g), DMSO (16 mL), and acetic anhydride (8 mL) was maintained at ∼150 ∘ C in an oil bath for eight hours.TLC monitoring indicated formation of a mixture of products.The reaction mixture was cooled, diluted with excess of water, and extracted with ether.The ether layer was washed several times with water and dried over anhydrous sodium sulphate and removal of solvent afforded a gummy residue, column chromatography of which over silica gel gave only one pure product in good yields m.p. 244-246 ∘ C. The compound was found to be devoid of sulphur: Ylide (1a), yield (52.5%), m.p. 165 ∘ C 1 HNMR CDCl3, 300 MHz, (), ppm),

Results and Discussion
The reaction between 1,3-indandione and DMSO/Ac 2 O reagent at room temperature has been found to afford an unusual dimer 1H,1  H-2,2  -biindene-1,1  ,3,3  (2H,2  H)tetrone, a dimeric condensation product along with an ylide (1a) in better yields than those reported earlier [15].However, when 1,3-indandione was refluxed with this versatile reagent at 150 ∘ C (±5 ∘ C), the reaction proved to be destructive; that is, instead of two enantiomers TLC monitoring indicated the formation of a number of products which could not be resolved.Workup of the reaction mixture and chromatography of the material resulted in only one pure compound m.p. 244-246 ∘ C and was found to be devoid of sulphur.On the basis of elemental analysis and mass spectrum showing M + at / 316, its molecular formula was found to be C 20 H 12 O 4 and the structure ultimately assigned to this compound is (2) (Figures 1 and 2).
The 1 HNMR spectrum of this compound was extremely simple showing two singlets equivalent to two protons each at  2.48 and 3.34 and a multiplet equivalent to eight protons in the aromatic region at  7.20-7.97.This suggests involvement of two indandione molecules and two methylene groups most certainly derived from DMSO in the formation of this compound.The structure (2) assigned to this compound is also supported by its IR spectrum showing strong carbonyl bands at 1700 and 1710 cm −1 .It is analogous to the compound (3) obtained upon treatment of 1,3-indandione with formaldehyde in presence of primary amines [16] (Figure 3).
Formation of this compound at elevated temperature (150 ∘ C) is understandable on the basis that 2-hydroxymethyl or 2-methylthiomethyl-1,3-indandione initially formed in this reaction can decompose at this temperature to yield (4) dimerisation of which through Diels Alder reaction gives the Spiro product (2) (Scheme 1).

Conclusion
Synthesis of this novel compound was confirmed by different spectral techniques.Its IR and 1 HNMR studies suggest the oxidative cyclizations involving methylene group of one indandione moiety and the carbonyl group of the other.Silica gel used for chromatographic techniques worked as a good adsorbent and showed better resolution than other adsorbents.