Rhodium(II)-Catalyzed Aziridination of Allyl-Substituted Sulfonamides and Carbamates

Several unsaturated sulfonamides underwent intramolecular aziridination when treated with PhI(OAc)2, MgO, and catalytic Rh2(OAc)4 to give bicyclic aziridines in excellent yield. Treatment of
the resulting azabicyclic sulfonamides in methanol in the presence of p-TsOH resulted in exclusive
opening of the aziridine ring at the most substituted position affording six- and seven-membered
ring products in high yield. In contrast, the intramolecular aziridination of several cycloalkenyl-substituted carbamates did not require a Rh(II) catalyst and proceeded via an iminoiodinane
intermediate. The resulting tricyclic aziridines underwent ring opening when treated with various
nucleophiles to give anti-derived products as expected for nucleophilic attack at the three-membered
ring. The iodine(III)-mediated reaction of a 3-indolyl-substituted carbamate, however, required a
Rh(II) catalyst. The expected aziridine was not observed, but rather simultaneous spirocyclization
of C3 and stereoselective syn-acylation at C2 occurred to give compound 41, whose structure was
unequivocally established by an X-ray crystallographic study. The reaction proceeds in a stepwise
manner via a metal-free zwitterionic intermediate which is attacked by a nucleophilic reagent on
the same side of the amide anion. Related reactions occurred with both a 2-indolyl- and
3-benzofuranyl-substituted carbamate but with lower stereoselectivity.