Synthesis of Azido-Dienediols by Enzymatic Dioxygenation of Benzylazides: An Experimental and Theoretical Study

Allylic azides are versatile structural motifs in organic synthesis because the proximal double bond enables a [3,3]-sigmatropic rearrangement, named as the Winstein rearrangement. In this work, an experimental and theoretical study on the double Winstein rearrangement occurring in azidodienediols derived from the biocatalytic dihydroxylation of substituted benzylazides is presented. Substrates bearing a methyl group at the ortho or meta position produced exclusively rearranged exo-diendiols with the azide group anti to the diol moiety as the major constituent. In the case of para methyl substrates, an equilibrium mixture of rearranged and non-rearranged products was observed, indicating that a full conversion to the exo-dienediols is not possible within this substitution pattern. On the other hand, the presence of a chloro substituent in the diene moiety completely precluded the Winstein rearrangement to take place, giving rise exclusively to the traditional cis-cyclohexadienediols. The observed results were analyzed to determine the mechanistic and kinetic aspects and scope limitations of the reaction as a synthetic tool.