Exploring hydroamination-cycloaddition-fragmentation sequences to access polycyclicguanidines and vinyl-2-aminoimidazoles

Abstract

The intramolecular hydroamination of a guanidine on an eneyne unit affords a guanidine-substituted diene capable of reacting with dienophiles. These substrates undergo [4+2]-cycloaddition reactions to generate a series of complex cyclic- and spirocyclic-guanidines. Select substrates can further undergo a ring opening-elimination cascade that ultimately reveals a vinyl-2-aminoimidazole. As such this cascade reaction may find application in the synthesis of oroidin-type natural products and their analogues

Tandem Radical Fragmentation/Cyclization of Guanidinylated Monosaccharides Grants Access to Medium-Sized Polyhydroxylated Heterocycles

“…Next, the selective deprotection of the anomeric alcohol, employing either Zemplén transesterification conditions or a hydrogenolysis promoted by Pearlman's catalyst, furnished the desired precursor hemiacetals for the fragmentation/cyclization reaction (12)(13)(14)(15)(16)(17).…”

“…Nevertheless, this time the internal nucleophile, a conveniently positioned Boc-protected guanidine group, would be responsible for the intramolecular cyclization, rather than an amido or an N -heterocyclic group. Another difference with earlier works arises from the bidentate character of the guanidine group as a nucleophile, which opens the possibility of differentiating between the two nonequivalent nitrogen atoms, thus making the proposed methodology more versatile, as products of different sizes (endocyclic vs exocyclic guanidine) could be generated (Scheme ).…”