Stereospezifische Synthese einer neuen Morphin-Teilstruktur

We describe here a synthesis of the morphine partial structures 28 and 36 , and of their enantiomers, which uses 7-methoxy-benzofurancarboxylic acid as starting material. A key intermediate in this scheme is compound 15 , which is converted, via 1,2-ketone shift, into 22 . This latter is stereospecifically reduced to the alcohol 24 and converted to the amide 25 . The diastereomer of 25 is afforded by stereospecific introduction of a ethoxycarbonyl group in 15 to yield the β-ketoester 31 , followed by Curtius degradation of the acid 32 to the acylamine 34 . An efficient method for removal of the methoxy group in methoxy-dihydro-benzofurans is presented (Scheme 9), as is the functionalization of the N-atom in 27 with concurrent complex formation between the free hydroxy group and boric-acid. The aromatization of the furan ring (Scheme 10) with DDQ gave the expected benzofuran derivative 30 .