[joyb]

What is the mechanism for the reaction between formaldehyde, acetone and dimethylammonium to give [MeCOCH₂CH₂NHMe₂]⁺? I would guess a combination of the aldol reaction and addition-elimination to give an imine, but I'm having trouble getting the correct product from that.

[Dan]

I would guess a combination of the aldol reaction and addition-elimination to give an imine

Sounds like you are on the right track, you have the key reactivity concepts here.

I'm having trouble getting the correct product from that

We can't help to explain where you're going wrong unless you show what you've done.

[someonefromasia]

What is the mechanism for the reaction between formaldehyde, acetone and dimethylammonium to give [MeCOCH₂CH₂NHMe₂]⁺? I would guess a combination of the aldol reaction and addition-elimination to give an imine, but I'm having trouble getting the correct product from that.

The amine first react with formaldehyde, kicking out water and forming H₂CNMe₂⁺Cl^-. Then the tautomer of acetone does an "aldo" reaction on it, giving the product.