The synthetic utility of 4-hydroxy-2-imidazolidinone amidoalkylation reactions is limited by the propensity of the carbon-5 unsubstituted and carbon-5 monosubstituted adducts to undergo dehydration to yield 2-imidrrZolones. Two techniques are reported which avoided this competitive side reaction. The first approach utilized reactive allyl silanes. Treatment of substituted 4-hydroxy-2-imidazolidinones 16 with allyltrimethylsilane (17) under Lewis ...