Diaza [1,4] Wittig-type rearrangement of N-allylic-N-Boc-hydrazines into gamma-amino-N-Boc-enamines

What is it about?

The base-promoted [1,4] Wittig rearrangement of alkyl allylic ethers to generate enolates is a unique transformation in organic synthesis; however, the aza-version of this [1,4] rearrangement using allylic amine derivatives as substrates is severely limited. In the current paper, we applied this protocol to N-allylic-N-Boc-hydrazine derivatives and investigated their base-promoted [1,4] rearrangement involving a nitrogen–nitrogen bond cleavage. The 1,4-shift of an amino migrating group into the gamma-position of the allylic moiety provided synthetically valuable gamma-amino enamides with E-selectivities. We termed this reaction a “diaza [1,4] Wittig rearrangement”. The scope and limitations, experimental mechanistic studies, and a proposed reaction mechanism are also described.

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Why is it important?

Although the diaza [1,4] Wittig rearrangement demonstrated in this manuscript still has substrate limitations, our method provides unique access to substituted N-Boc-enamides. This study will expand the synthetic scope and utility of not only the Wittig rearrangement but also analogous sigmatropic rearrangements.