Generation and Reactivity of 2-Amido-1,3-diaminoallyl Cations: Cyclic Guanidine Annulations via Net (3+2) and (4+3) Cycloadditions

Abstract

Toward a method for direct conversion of alkenes to cyclic guanidines, we report that 1,3-dipolar cycloadditions of 2-amido-1,3-diamino allylic cations with electron rich alkenes provides a new method for direct cyclic guanidine annulation. Generated under oxidative conditions, the 2-amido-1,3-diaminoallyl cations, react as 1,3-dipoles providing rapid access to 2-amino imidazolines through net (3+2) cycloadditions. The utility is demonstrated through a concise synthesis of the oroidin alkaloid, phakellin. The described 1,3-dipole also participates in net (4+3) cycloadditions with dienes. Several observations suggest a stepwise, ionic, net cycloaddition leading to initial carbocation formation as evidenced by initial formation of constitutional isomers and intervening eliminations. Complex aziridines are formed with dienes suggestive of nitrene intermediates and results in net tetra-functionalization of dienes.<br>