The Squalestatins: Cleavage of the Bicyclic Core via the Novel 6,8-Dioxabicyclo(3.2.1)octane Ring System.

Squalestatin S1 1 has been converted into its 4,7-bis(2-methoxyethoxymethyl)ether 4,5-dimethyl ester 11 and thence to its 3-(tert-butoxycarbonyl)amino derivative 12via a Schmidt degradation. Acid-catalysed hydrolysis of 12 brought about a molecular rearrangement of the 2,8-dioxa- to the novel 6,8-dioxa-bicyclo[3.2.1]octane ring system 3. Oxidation of 3 followed by methanolysis gave the novel spiroketal 17. Treatment of 3 with trimethyl phosphonoacetate gave the acyclic derivative 18.