Sharpless epoxidation Claisen

The (panial) description of the synthesis and coupling of the live fragments starts with the cyclohexyl moiety C21—CM The first step involved the enantio- and diastereoselective Sharpless epoxidation of l,4-pentadien-3-ol described on p 126f The epoxide was converted m four steps to a 3-vinyl 6-lactone which gave a 3-cydohexenecarboxylate via Ireland-Claisen rearrangement (cf p 87) Uncatalysed hydroboration and oxidation (cf. p 131) yielded the desired muis-2-methoxycydohexanol which was protected as a silyl ether The methyl car-... 

The homochiral acetylenic alcohol 2 [derived from ( )-4-benzyloxy-2-butenol by asymmetric Sharpless epoxidation via 2 in four steps] is transformed either to ( )-3 by treatment w ith lithium aluminum hydride or to (Z)-4 by hydrogenation with Lindlar catalyst. Simple Claisen or ortho ester rearrangement yield the same, but enantiomeric, products 5 and 6 with 85-90% ee288. 

In the enantioselective synthesis of the C-l-C-28 portion of cytotoxic marine natural product amphidinolide B1217, Lee [47] developed a strategy using the key steps of the Evans oxazohdinone alkylation, Sharpless epoxidation and orthoester Claisen rearrangement AUylic alcohol 218 as a mixture of diastereomers gave rise after treatment with triethyl orthoacetate under acidic catalysis to ester 219 in 66% yield (Scheme 6.34). This result exemplifies the potency of the orthoester rearrangement even with such probably sensitive epoxyallylic alcohol. 

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