The 1,3-diaza Claisen rearrangement was initially discovered by the Madalengoitia group in the early 2000s. Tertiary, allylic, amines nucleophilically add to the carbon of a heterocumulene (isocyanate, isothiocyanate, or carbodiimide) to generate a zwitterion which then undergoes [3,3]-sigmatropic rearrangement. The rearrangements conducted with a carbodiimide generate guanidine-containing skeletons. The guanidine functional group is found in many biologically active products, making it a worthwhile chemical target. To this end, strained, tertiary, allylic, amine 2-benzyl-2-azabicyclo[2.2.1]hept-5-ene reacts with in-situ generated carbodiimides in the 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. The synthesis of such carbodiimides was explored through new synthetic methodologies for the dehydration of ureas and desulfurization of isothioureas and the carbodiimides were used in a series of intermolecular rearrangements with the strained, tertiary, allylic, amine. The new methodologies for the synthesis of electron deficient carbodiimides were then applied to a series of intramolecular substrates, further expanding the 1,3-diaza Claisen rearrangement methodologies. To date series of bicyclic, tricyclic, and monocyclic guanidines of varying structures have been synthesized. The synthetic efforts towards these products are herein described.