Optimization of methods for the generation of carbodiimides for zwitterionic 1,3-diaza-Claisen rearrangements

Abstract Strained, tertiary, allylic, amine 2-benzyl-2-azabicyclo[2.2.1]hept-5-ene reacts with in situ generated carbodiimides in a 1,3-diaza-Claisen rearrangement to afford structurally interesting bicyclic guanidines. Use of more electron deficient carbodiimides makes these rearrangements more facile; however, there are not sufficient methods for the synthesis of highly electron deficient carbodiimides. Herein reported is the exploration of the synthesis of such carbodiimides from parent ureas and isothioureas and their use in 1,3-diaza-Claisen rearrangements.