A simple and efficient synthesis of 2-imidazolin-2-ones

We report on the reactions of diazenes 1 and 2 with 1,3-dicarbonyl compounds. The first step involves a regioselective attack of the diazene on the active methylene group, giving the Michael adducts 3 or 4, and can be performed either in the presence of sodium acetate or DBN (1,5-diazabicyclo[ 4.3.0] non-5-ene). The Michael adducts underwent ring-closure leading to 2-imidazolidinones 5 or 6 which were isolated in some cases. We found that 5 or 6 easily eliminated water in the presence of an acid to give imidazolin-2-ones 7 or 8 as the final products. The rate-determining step of this last mentioned process depends on the stereochemistry at C4 and C5 of the initial 2-imidazolidinone. A one-pot procedure to produce 7 or 8 directly from the diazene and the appropriate dicarbonyl partner is also described.