Strain-release enabled [3 + 2] annulation of 3-aminooxetanes with simple CN bonds: facile synthesis of imidazolidines

An unprecedented [3 + 2] annulation of readily available 3-aminooxetanes and 1,3,5-triazinanes is accomplished for the first time. The BF3·Et2O promoted ring-opening of the strained oxetane motif is the thermodynamic driving force for this reaction. The prominent features of this reaction include simple operation, broad scope, and transition-metal-free and mild conditions, allowing the efficient synthesis of a range of structurally diverse 4-hydroxymethyl imidazolidines in useful to good yields (31 examples, up to 93% yield). The synthesis on a gram scale and downstream modification of imidazolidine products with some biologically active acids are successful.