Development of a Practical Synthesis of a Peripherally Selective Noradrenaline Reuptake Inhibitor Possessing a Chiral 6,7-trans-Disubstituted-1,4-oxazepane as a Scaffold

A practical synthesis of a peripherally selective noradrenaline reuptake inhibitor that has a chiral 6,7-trans-disubstituted-1,4-oxazepane as a new class of scaffold is described. The amino alcohol possessing the desired stereochemistry was obtained with excellent dr and ee, starting from a commercially available aldehyde via a Morita–Baylis–Hillman reaction, Michael addition, isolation as maleic acid salt, reduction, and diastereomeric salt formation with (+)-10-camphorsulfonic acid. The desired single stereoisomer obtained at an early stage of the synthesis was used for seven-membered ring formation in fully telescoped processes, providing the chiral 6,7-trans-disubstituted-1,4-oxazepane efficiently. In addition to controls of dr and ee of the chiral 1,4-oxazepane, and control of N,O-selectivity in SN2 reaction of the intermediate mesylate with a pyridone derivative, finding appropriate intermediates that were amenable to isolation and upgrade of purity enabled a practical chiral HPLC separation-free, column chromatograph-free synthesis of the drug candidate with excellent chemical and optical purities in a higher overall yield.