[3,3]-sigmatropic rearrangement to transfer an allyl group to the imminium carbon

[3,3]-sigmatropic rearrangement to transfer an allyl group to the imminium carbon
REACTION MECHANISM
Starting point is to react the secondary amine with the aldehyde to form a cyclic imminium structure. Once generated, this is nicely set up to undergo a [3,3]-sigmatropic rearrangement to transfer an allyl group to the imminium carbon. The resulting formaldehyde imminium product is then hydrolyzed in the presence of water to afford the product plus an equivalent of formaldehyde





closer inspection, you can see that there is one less carbon in the product than the starting material. Furthermore, there are no reducing agents present, only acid (and presumably water)