solution heated in an oil bath at 133 u00b0 c for 2 hrs the mixture was allowed to cool to room temperature and poured into a 3000 ml beaker ice and water 1400 ml were carefully added the mixture extracted with dcm 800 ml and the aqueous phase further extracted with dcm 300 ml the organic extracts were dried over sodium sulphate and the filtered solution concentrated in vacuo the residue was purified by flash chromatography over silica gel eluting with etoac heptane 1 15 to 1 10 v v to afford compound 35 as a colourless oil yield 77 g 51 electrospray ms m z 583 mh analytical hplc rt 29 16 mins 91 8 u25a1 h 500 mhz cdcl 3 1 35 6h s c c h 3 2 3 62 2h dd j 6 10 2 u00d7 c h oc 3 75 4h m 2 u00d7 c h 2 obn 4 15 4 20 1h m c h obn 4 46 1h dd j 12 5 14 5 c h obn 4 77 4h d j 11 5 4 u00d7 c h 2ac 6 h 5 4 73 4h d j 11 5 4 u00d7 c h 2b c 6 h 5 and 7 25 7 34 20h m 4 u00d7 c 6 h 5 in a 2000 ml flask fitted with a condenser compound 35 41 11 g 0 071 mol was dissolved in 70 acetic acid 700 ml and the solution stirred at 100 u00b0 c in an oil bath for 1 5 hrs after concentration in vacuo the residue was purified by flash chromatography over silica gel eluting.