Traceless bond construction via rearrangement of N-Boc-N-allylhydrazones giving 1,1-disubstituted olefins

An extension of a recently described olefin synthesis under traceless bond construction via triflimide (HNTf2)-catalyzed rearrangement of N-Boc-N-allylhydrazones is presented. This protocol opens a new approach to 1,1-disubstituted olefins. Application of this methodology to a new synthesis of episterol was hampered by undesired acid-catalyzed double bond isomerizations, but an unprecedented fragmentation of sterically hindered N-Boc-N-allylhydrazones to give nitriles was observed in this course. A reference sample of episterol was prepared utilizing new silyl-protected intermediates.