SYNTHESIS OF S)-4,5-DIHYDRO-1,5-EPOXY-1H-2-BENZOXOCIN-6(3H)-ONE FROM (S)-MALIC ACID-DERIVATIVES

The homochiral 1,3-dioxanes 8a-e with a 2-bromophenyl substituent in p osition 2 and an electrophilic group in position 4 were stereo- and re gioselectively prepared from the (S)-malic acid derivatives 6a, 6b, 11 , and 14. Attempts to prepare the tricycles 5a-c by connecting the 2-p henyl substituent with the electrophilic groups in position 4 of 8a-e in a Parham cyclization across the 1,3-dioxane ring failed. The synthe sis of the tricyclic title ketone 5a succeeded, however, by addition o f the Lithiated benzaldehyde acetal 7c to the protected alpha-hydroxyl actone 10b and subsequent treatment of the intermediate ketone 23 with acid. The acid hydrolysis of the alcohol 26, which was obtained by ad dition of 7c to the protected dihydroxy aldehyde 25b, followed by oxid ation of the resulting alcohols 27a and b represent a second possibili ty for the preparation of the tricyclic ketone 5a.