Doubly diastereoselective [3,3]-sigmatropic aza-Claisen rearrangements.

The doubly diastereoselective [3,3]-sigmatropic aza-Claisen rearrangement of silylketene aminals derived from 5-substituted (3S,4E,alphaR)-1-benzyloxy-3-[N-acyl-N-(alpha-methylbenzyl)amino]pent-4-enes furnishes 2,3-disubstituted (R)-N-alpha-methylbenzyl (2S,3R,4E)-7-benzyloxyhept-4-enamides in >90% de under the "matched" control of both stereogenic centres. Rearrangement of the "mismatched" diastereomeric (3R,4E,alphaR)-substrates proceeds with low diastereoselectivity. The substrate scope of the doubly diastereoselective rearrangement of the "matched" substrates in which two new stereogenic centres are created has been delineated.