Anisaldehyde dimethylacetal

The C-ring of morphine was prepared fi om tri-O-acetyl-D-glucal (66) as shown in Scheme 10. Saponification of the acetate moieties in 66 under basic conditions was followed by treatment with p-anisaldehyde dimethylacetal before the C6 hydroxy functionality (morphine numbering) was protected as its sUyl ether (67). 

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