Eschenmoser-Claisen-type rearrangement

The synthesis of three fragments 278, 282, and 285 for the C21-C42 bottom segment is summarized in Scheme 41. The Eschenmoser-Claisen rearrangement of amido acetal of 276, which was prepared via 2-bromocyclohexenone by Corey s asymmetric reduction, afforded amide 277. Functional group manipulation including chain elongation provided Evans-type amide 278. The Evans aldol reaction of boron enolate of 279 with aldehyde 280 stereoselectively afforded 281, which was converted into aldehyde 282 through a sequence of seven steps... 

Zhang and Danishefsky reported the first total synthesis of ( )-2 [13]. Their retrosynthetic plan for ( )-2 is illustrated in Scheme 1. The first cmcial step in this contemplated scheme is envisaged to start with the stereoselective Eschenmoser-Claisen rearrangement [15] of allyl alcohol 13 to constmct the requisite transdecalm portion 11 via intermediate 12. Rearrangement precursor 13 is accessible starting fi-om ( )-5-methyl-Wieland-Miescher ketone (15) via trans-decalone 14. The second critical step is envisioned to involve the aldol-type coupling reaction of methyl ester 10 with the known aldehyde 9 [16] to assemble the requisite... 

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