Convenient Preparation of Dimethyl [(3S)‐3‐Methyl‐2‐oxo‐5‐octynyl]‐phosphonate

The diastereoselective alkylation of the chiral Evans intermediate 2 with 1‐iodo‐2‐pentyne (3) gives the oxazolidinone 4. Titanium alkoxide‐catalysed cleavage yields the ethyl ester 5, which is used to acylate dimethyl methanephosphonate to the chiral phosphonate 6. The optical purity of phosphonate 6 is checked by separation on a chiral HPLC column and by conversion into the bromo ketone 8, an intermediate for the prostacyclin analogue ZK 96480.