Myers total synthesis of -neocarzinostatin

In order to prevent competing homoallylic asymmetric epoxidation (AE, which, it will be recalled, preferentially delivers the opposite enantiomer to that of the allylic alcohol AE), the primary alcohol in 12 was selectively blocked as a thexyldimethylsilyl ether. Conventional Sharpless AE7 with the oxidant derived from (—)-diethyl tartrate, titanium tetraisopropoxide, and f-butyl hydroperoxide next furnished the anticipated a, [3-epoxy alcohol 13 with excellent stereocontrol (for a more detailed discussion of the Sharpless AE see section 8.4). Selective O-desilylation was then effected with HF-triethylamine complex. The resulting diol was protected as a base-stable O-isopropylidene acetal using 2-methoxypropene and a catalytic quantity of p-toluenesulfonic acid in dimethylformamide (DMF). Note how this blocking protocol was fully compatible with the acid-labile epoxide. 

Deprotonation of the terminal acetylene in epoxydiyne 7 was next attempted with lithium hexamethyldisilazide in toluene at low temperature. The resulting lithium acetylide added readily to cyclopentenone 69 

However, it is the high P=0 bond energy in Ph3P=0 which clearly helps offset this dubious energy trade-off. 

With the neocarzinostatin aglycone 1 now successfully assembled, the time had arrived for connecting the sugar unit to the cyclopentene ring.2b Somewhat surprisingly, a wide range of Lewis acid promoters proved 

It is likely that the phenolic hydroxyl of 1 is much less nucleophilic than the allylic OH because of its involvement in strong intramolecular hydrogen bonding with the ortho carbonyl of the ester. This would 

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