[lutesium]

How does this reaction occur? After the methylation of the S Atom which group becomes the leaving group??? Is there a name reaction for this???

Thanks!!!

[Smrt guy]

I've never seen this but I suspect that first is an addition/elimination mechanism to form the guanidine derivative after MeS- leaves.  I suspect that the next step is like formation of an imine from a carbonyl.  The entropic favorability likely pushes the reaction to completion.

[Violet]

What's the condition of the reaction between 1 and diaminoethane? I suppose it happened in aqeous solution so the imine in 1 will hydrolyze to carbonyl first, then form a new imine with diamine followed by a nucleophilic attack from another amino group. Then the tetrahedron intermediate will collapse and kick off the CH3S- group to give a stable 5 member ring.
All the above are just guessing.

[Smrt guy]

I think that water would mess up the reaction, giving a urea derivative.