1,4-addition of nucleophiles to enones
Description: Alpha beta unsaturated ketones can undergo reaction with a variety of nucleophiles to form 1,4-addition products (aka “Michael products”)
Notes: If the nucleophile is negatively charged, such as RO(–), RS(–), HO(–), NC(–) etc., acid will be needed in the second step. If the nucleophile is neutral such as RNH2 or RSH, then the second step will be a proton transfer.
Ketones or aldehydes with an alkene adjacent to them are referred to as “alpha, beta unsaturated”.
Mechanism: The negatively charged nucleophile attacks the beta carbon of the α,β-unsaturated ketone (C–4 in this case), producing an enolate (Step 1, arrows A and B). Protonation (Step 2, arrows C and D) produces the neutral product.
Nothing special about Cl here, it’s just a spectator ion to balance out H3O(+)
The products of these reactions are extremely prone to elimination through E1cb mechanisms, or through tautomerism.