method for the preparation of enantiomerically pure mirtazapine; and, method for selecting an appropriate acid or solvent / acid combination for a stereospecifically ring-closing reaction of enantiomerically pure compound

摘要

"METHOD FOR PREPARING ENANTIOMERICALLY PURE MIRTAZAPINE, AND METHOD FOR SELECTING AN ACID / SOLVENT APPROPRIATE FOR A STEREO SPECIFICLY COMPOUND COMPOUND RING CLOSING REACTION. The invention provides a method for the preparation of enantiomerically pure mirtazapine, comprising a ring closing step of a compound of formula (II) wherein X is a leaving group, the step of which comprises treatment with an acid, whereby mirtazapine Enantiomeric excess is formed by ring-closing of the enantiomeric excess compound of formula (II) by treatment with an appropriate acid in the absence of a solvent or an appropriate combination of an acid and an organic solvent.