合成路线1

The reaction of 2,3-dihydrobenzofuran (I) with dichloromethyl methyl ether (II) by means of TiCl4 in dichloromethane gives 2,3-dihydrobenzofuran-5-carbaldehyde (III), which is condensed with the phosphonate (IV) by means of NaH in THF to yield the propenoic ester (V). The reduction of (V) with H2 over Pd/C in ethanol affords the saturated propionic ester (VI), which is brominated with Br2 in HOAc providing the 7-bromo derivative (VII). Further bromination of (VII) with Br2 and Fe in HOAc gives the 6,7-dibromo derivative (VIII), which is hydrolyzed with NaOH in THF/water to yield the propionic acid derivative (IX). The reaction of (IX) with hot SOCl2 affords the corresponding acyl chloride (X), which is cyclized by means of AlCl3 in dichloroethane to provide 4,5-dibromo-2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-one (XI). The debromination of (XI) by means of H2 over Pd/C in Ac-OH gives 2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-one (XII), which is condensed with the phosphorane (XIII) by means of NaH in THF to yield 2-(2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-ylidene)acetonitrile (XIV). The selective reduction of the cyano group of (XIV) by means of H2 over Raney cobalt in ethanol/NH3 affords 2-(2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-ylidene)ethylamine (XV), which is condensed with propionyl chloride (XVI) by means of TEA in THF to provide the propionamide (XVII). Finally this compound is enantioselectively reduced with H2 over a chiral Ru catalyst (Ru(OAc)2-(S)-BINAP) in methanol to give rise to the target (S)-enantiomer. Alternatively, the reduction of 2-(2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-ylidene)acetonitrile (XIV) with H2 over RaNi in ethanol/NH3 gives 2-(2,6,7,8-tetrahydro-1H-indeno[5,4-b]furan-8-yl)ethylamine (XVIII), which is acylated with propionyl chloride (XVI) and TEA in DMF to yield the racemic propionamide (XIX). Finally this compound is submitted to optical resolution by means of chiral HPLC to afford the target (S)-enantiomer.

合成路线2