Synthesis of the potassium channel opener (3S,4R)-3,4-dihydro-4-(2,3-dihydro-2-methyl-3-oxo-pyridazin-6-Yl)oxy-3-hydroxy-6-(3-hydroxyphenyl)sulphonyl-2,2,3-trimethyl-2H-benzo[b]pyran

The preparation of the potassium channel opener (3S,4R)-3,4-dihydro-4(2,3-dihydro-2-methyl-3-oxo-pyridazin-6-yl)oxy-3-hydroxy-6-(3-hydroxyphenyl)sulphonyl-2,2,3-trimethyl-2H-benzo[b]pyran (1) as a single enantiomer is reported. Considerable improvements have been implemented with respect to the original synthesis that allow for the preparation of multigram quantities of the final target compound. The optimized synthesis consists of a six-step linear sequence whose key step is an asymmetric epoxidation protocol through the use of Jacobsen's (S,S)-(+)-N,N'-bis(3,5-ditert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride catalyst.