合成路线1

The pyrrolo-oxazine fragments, the free base (II) or the Boc-protected (V) can be synthesized as follows. Butene-1,4-diol (XXIV) is subjected to either of the two following alternative procedures: 1) treatment with mesyl chloride in the presence of Et3N in CH2Cl2 and subsequent reaction with tosylamine, NaOH and tetrabutylammonium hydrogensulfate (TBAHS) in toluene/water at 40 °C (1, 2); or 2) chlorination with thionyl chloride followed by treatment with tosylamide by means of NaH in DMF (3) to afford 1-tosyl-2,5-dihydro-1H-pyrrole (XXV). Compound (XXV) is then epoxidated with meta-chloroperbenzoic acid (mCPBA) in refluxing dichloromethane to yield cis-N-tosyl-6-oxa-3-azabicyclo[3.1.0]hexane (XXVI) (1-3). Desymmetrization of intermediate (XXVI) is carried out by condensation with ethanolamine (XXVII) in refluxing dichloromethane to yield the racemic N-alkylated pyrrolidine derivative rac-(XXVIII), which by reaction with tosyl chloride in pyridine/THF at –10 °C affords the tosylate rac-(XXIX). Cyclization of the racemic (XXIX) by means of NaOH in THF/methanol at 0-3 °C gives the racemic pyrrolo-oxazine rac-(XXX), from which the desired enantiomer (4aS,7aS)-octahydropyrrolo[3,4-b][1,4]oxazine (XXX) is separated by chiral chromatography. Finally, compound (XXX) is detosylated by means of HBr/AcOH and anisole at 60 °C and the resulting dihydrobromide salt (XXXI) is treated with potassium hydroxide in isopropanol to afford the free base intermediate (II) (1). Scheme 3.
In an improved method for intermediate (II), compound (XXVI) is desymmetrized by coupling with (R)-phenylethylamine (XXXII) in water (2, 3), resulting in a mixture of diastereomers that is resolved by crystallization (2) or chromatography (3). The desired isomer (XXXIII) is N-acylated with chloroacetyl chloride (XXXIV) by means of triethylamine (2) or DIEA in THF (3) to afford the N-chloroacetyl amine (XXXV), which then cyclizes in the presence of sodium hydroxide (2) or potassium tert-butoxide in dichloromethane (3). The resulting bicyclic lactam (XXXVI) is reduced with LiAlH4 in THF (3) or NaBH4 in the presence of BF3.THF complex (2) to give the pyrrolooxazine derivative (XXXVII) (2, 3), which is detosylated by treatment with HCl and subsequently with NaOH, yielding the free amine (XXXVIII). Finally, compound (XXXVIII) is subjected to hydrogenolysis over Pd/C in methanol to afford the target (4aS,7aS)-octahydropyrrolo[3,4-b][1,4]oxazine (II) (2). Scheme 3.
The Boc-protected compound (V) is obtained by subjecting N-alkylated derivative (XXXVII) to hydrogenolysis over Pd/C in methanol followed by treatment with tert-butoxycarbonyl anhydride in dichloromethane. The resulting fully protected intermediate (XXXIX) is finally detosylated with sodium naphthalenide (3). Scheme 3.