equivalents of mg clo 9 2 are added after 30 min 0 95 equivalents of n chlorosuccinimide are added in 2 h at the end of the addition the resulting mixture is stirred for 1 hour at room temperature then the solid formed is eliminated the clear solution is transferred into a separating funnel after diluting with other 350 ml of ethyl acetate the organic phase is washed with brine h 2 o and dried on na 2 so 4 the solvent is evaporated obtaining 34 g of crude chlorine derivative hplc purity 79 40 u03bb 280 nm which is used in the subsequent reaction without further purification 34 g of crude chloro u03b2 keto ester r are refluxed with hcooh 100 ml ch 3 cooh 120 ml and h 2 o 30 ml after 1 5 h a control by hplc highlights the end of the reaction the mixture is then evaporated under reduced pressure taken up with ethyl acetate and the organic phase is washed with brine saturated nahco 3 h 2 o and dried on na 2 so 4 then the solvent is evaporated under reduced pressure obtaining 21 g of u03b1 chloro ketone hplc purity 60 u03bb 280 nm as an oil that is used tel quel for the next step without further purification 21 g of the oil obtained from the preceding reaction are dissolved in 15 volumes of meoh to this solution 2 0 equivalents of nabh ococh 3 3 are added with a spatula and it is kept under magnetic stirring at room temperature.