Indian Journal of Chemistry Vol. 46B, June 2007, pp. 1038-1041 Note Unusual KMnO 4 oxidation product of β-ionone Shrivallabh P Kamat a *, Asha M D’Souza a , Shashikumar K Paknikar b , Mohan M Bhadbhade c & Rajesh G Gonnade c a Department of Chemistry, Goa University, Goa 403 206, India b Siddharth Chemicals, Kundai Industrial Estate, Kundai, Goa 403 115, India c Center for Materials Characterization, National Chemical Laboratory, Pune 411 008, India Email: shrivkamat@yahoo.com Received 25 July 2006; accepted (revised) 6 February 2007 KMnO 4 oxidation of β-ionone has been reinvestigated. The structure proposed for the hydroxyionolactone 3 obtained in this reaction is supported by MS, UV, IR, 1 H and 13 C NMR data and further confirmed by single crystal X-ray diffraction studies of the bromolactone 8. Keywords: β-ionone, KMnO 4 oxidation, hydroxyionolactone, bromolactone, crystal structure, X-ray diffraction The hydroxyionolactone obtained 1 by KMnO 4 oxidation of β-ionone 1 was formulated 2 as β-lactone 2 which was further revised 3 to structure 3 on the basis of its elemental analysis, UV and IR spectral data. However, no mass, 1 H and 13 C NMR spectra were recorded which would support the structure 3. Moreover, formation of 3 by KMnO 4 oxidation of 1 seemed interesting from the mechanistic point of view. Therefore, we repeated the KMnO 4 oxidation of 1 and obtained hydroxyionolactone as a crystalline solid, m.p. 122 o C. All the structural features of 3 including the conjugated enol lactone butenolide part are consistent with the UV, IR, 1 H and 13 C NMR data. Its 1 H NMR showed three singlets (δ 1.19, 1.46, 1.53), each integrating for three protons corresponding to two tertiary methyl groups (gemdimethyl) at C 4 and a tertiary methyl at C 7a respectively. The three methylene Hs appeared as multiplets in the region δ 1.5-2.27. The 13 C NMR signals for all the eleven carbons fully support the structure 3. The DEPT and H decoupled 13 C NMR spectra exhibited three sp 3 methyls (δ 25.24, 25.66, 29.67), three sp 3 methylenes (δ 19.94, 39.03, 41.6) and five quaternary carbons (δ 35.81, 85.13, 133.39, 141.27, 170.07). The high resolution CIMS showed M + peak at m/z 219 (100% M + + Na) and 196 (M + ), corresponding to the molecular formula C 11 H 16 O 3 . The genesis of the major fragment ions is presented below in Scheme I. Although Brooks and co-workers 3 have suggested the formation of 3 through the intermediate α-keto acid 4, it is not clear how 4 is formed. We believe that, the initially formed manganate ester 5 undergoes a cleavage* to give the α-keto aldehyde 7 via the Mn(III) complex 6. Further oxidation of 7 to the α- keto acid 4 followed by cyclization gives 3 (Scheme II). Hydroxyionolactone 3 is reported 1 to form a bromolactone 8 on treatment with hydrobromic acid under unstated 1 conditions and by the addition of bromine to the aqueous solution of the l actone 3 (ref 3). However, the bromolactone obtained using these methods melted over a range (166-73 o C) and was considered to be a mixture of stereoisomers 3 . The bromolactone 8 was prepared in 92% yield by generating bromine in-situ using potassium bromate and hydrobromic acid in glacial acetic acid 5 (Scheme III). Compound 8, a pale yellow crystalline solid that melted at 214 o C with decomposition was analyzed for C 11 H 15 O 3 Br (MS). The IR spectrum showed the presence of carbonyl band at 1790 cm -1 and the absence of the hydroxyl functionality. The 1 H NMR spectrum of 8 could nicely account for all the 15 H present as 3 methyls (9 H) and 3 methylenes (6 H) as follows: δ 1.29 (s, 3H, C 4 -CH 3 ), 1.46 (s, 3H, C 4 -CH 3 ), 1.53-1.75 (m, 4H, C 5 , and C 6 H), 1.79 (s, 3H, C 8 -H), 2.48 (m, 1H, C 7 -H), 2.52 (m, 1H, C 7 -H). The H decoupled 13 C NMR spectrum of 8 showed distinct 11 signals. Further support to the structure was found in O 1 O OH O 2 O O OH 3 ⎯⎯⎯⎯⎯⎯ ∗A similar cleavage without participation of the carbonyl group has been reported earlier 4 .