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

Syntheses and Transformations of 2,6‐Epoxy‐4 H ‐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 CH 3 I and aldehydes to afford the 5‐substituted epoxybenzoxocinones 18 and 20 .