Carbanion-Accelerated Claisen Rearrangements. 7. Phosphine Oxide and Phosphonate Anion Stabilizing Groups

The utility of phosphine oxide and phosphonate groups has been examined in the context of the carbanion-accelerated Claisen rearrangement (CACR). Both of the groups permit the construction of substituted allyl vinyl ethers by allyl oxide addition to phosphorus-substituted allenes. Extensive optimization was required to suppress isomerization of both the allenes and the vinyl ethers. Using potassium dimsylate and lithium chloride as the base, both the phosphine oxides and phosphonates rearranged readily at room temperature with complete regioselectivity in good yield (62-93%). The phosphonates also showed a high level of diastereoselectivity (92% de). The characteristic features of the CACR were compared with the original arylsulfone version.