Diethyl Ether → Dimethyl (2-oxohept-5-yn-1-yl)phosphonate

To a solution of 3.2 g of dimethyl methanephosphonate in 52 ml of tetrahydrofuran was added at -78° C. 155 ml of n-butyl lithium (1.59N) and the mixture was stirred for 25 mins at -78° C. To the mixture was added at -78° C. a solution of 1.6 g of the above-mentioned ester in 3.2 ml of tetrahydrofuran. The mixture was stirred for 15 mins and for one hour at room temperature. After addition of 100 ml of ether to the reaction mixture, the mixture was washed with 30 ml of aqueous saturated solution of oxalic acid, 50 ml of water and 40 ml of aqueous saturated solution of sodium chloride. The washed mixture was dried and concentrated to give an oily material. The oily material was distilled under reduced pressure to yield 2.2 g of dimethyl 2-oxo-hept-5-yne-phosphonate (143° to 146° C./0.7 mmHg).