Synthesen und Umsetzungen von 2,6-Epoxy-4H-3-benzoxocin-4-onen

Abstract

Syntheses and Transformations of 2,6-Epoxy-4H-3-benzoxocin-4-ones Four variations for the preparation of 5 are described: acid-catalyzed cyclisation of the methoxy acid 4a, base-catalyzed lactonisation of the hydroxy ester 6b, DCC-mediated dehydration of the hydroxy acid 6a and PCC oxidation of the hemiacetals 17a and 17b. By three steps the key intermediate 4a is prepared by addition of the lithium enolate of methyl acetate to the aldehyde 7 with subsequent cyclisation and saponification. Alternatively, addition of the acetic acid dianion to 7 followed by acidic work-up yields 4a in a one-pot procedure. Hydrolysis of 4a and 4b with dilute HCl gives the hemiacetals 6a and 6b, respectively. After deprotonation with LDA, 5b reacts with CH3I and aldehydes to afford the 5-substituted epoxybenzoxocinones 18 and 20.