u00b0 c and stirred for 25 h after completion of the reaction the ethyl acetate layer was separated at 20 30 u00b0 c added dm water 375 ml and adjusted the ph to 0 8 1 0 with dilute hydrochloric acid at 20 30 u00b0 c the aqueous layer was separated and extracted the product in to toluene 430 ml by adjusting the ph to 8 0 8 5 with 20 w w aqueous sodium carbonate solution the toluene layer was washed with dm water 225 ml concentrated under reduced pressure and dissolved in toluene 450 ml the toluene solution obtained in stage 1 was cooled to 5 10 u00b0 c and 2 6 lutidine 32 45 g 0 303 moles followed by valeryl chloride 36 54 g 0 303 moles were added at 5 10 u00b0 c in 1 h after addition the reaction mass temperature was raised to 25 30 u00b0 c and stirred for 1 h dm water 225 ml was added to the reaction at 20 30 u00b0 c separated the organic layer and washed with 5 w w aqueous sodium carbonate solution 75 ml tri n butyltin chloride 242 32 g 0 744 moles and sodium azide 50 18 g 0 772 moles were added to the organic layer containing n 1 oxopentyl n 2 u2032 2 tributyltintetrazol 5 yl 1 1 u2032 biphenyl 4 yl methyl l valine methyl.