Dianion Equivalents Corresponding to the Polypropionate Domain of Epothilone

Dianion Equivalents Corresponding to the Polypropionate Domain of Epothilone B 

4 1 ds) (f) TrocCl, pyridine, CH2CI2 then 0.5 M HCI/MeOH (86%, 2 steps) (g) TrocCl, pyridine, CH2CI2, (86%) (h) TMSCHN2, Hunig s Base, CH3CN, MeOH, (81 %)  

Unfortunately, more durable blocking groups could not be introduced onto the C7 hydroxyl center by trapping of the desired hydroxy ketone 59a. 

Although our initial attempts in this direction proved unavailing, our efforts were not completely futile in that we were able to confirm that the critical aldol reaction with S-aldehyde 63 did indeed provide the desired C6-C7 syn and C7-C8 anti relationship (by anti-Felkin Ahn addition) as the major diastereomer. 

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