Acyclic stereocontrol through the dianionic Claisen rearrangement of β-hydroxy esters: Synthesis of (±)-botryodiplodin

Dianionic Claisen rearrangements of (E)- and (Z)-butenyl β-hydroxy esters afford moderate stereoselection in the construction of highly functionalized acyclic systems. The reaction proceeds with remote stereocontrol and the resulting products display three contiguous chiral centers, C(α) and C(β′) stereocenters being established in the rearrangement (cf. 1z → 3b). Experiments are described which unambiguously establish that each dianionic Claisen proceeds with excellent diastereoface selectivity [C(α),C(β) stereocontrol] and moderate chair/boat selectivity [C(α),C(β′) stereocontrol]. Application of this Claisen protocol to a synthesis of the mycotoxin botryodiplodin is also described (1z → 8b).