Metalloporphyrin-Mediated Asymmetric Nitrogen-Atom Transfer to Hydrocarbons: Aziridination of Alkenes and Amidation of Saturated C−H Bonds Catalyzed by Chiral Ruthenium and Manganese Porphyrins

Authors:
Publisher website
Google Scholar
Abstract
Chiral metalloporphyrins [Mn(Por*)(OH)(MeOH)] (1) and [Ru(Por*)(CO)(EtOH)] (2) catalyze asymmetric aziridination of aromatic alkenes and asymmetric amidation of benzylic hydrocarbons to give moderate enantiomeric excesses. The mass balance in these nitrogen‐atom‐transfer processes has been examined. With PhI=NTs as the nitrogen source, the aziridination of styrenes, trans‐stilbene, 2‐vinylnaphthalene, indene, and 2,2‐dimethylchromene catalyzed by complex 1 or 2 resulted in up to 99 % substrate conversions and up to 94 % aziridine selectivities, whereas the amidation of ethylbenzenes, indan, tetralin, 1‐, and 2‐ethylnaphthalene catalyzed by complex 2 led to substrate conversions of up to 32 % and amide selectivities of up to 91 %. Complex 1 or 2 can also catalyze the asymmetric amidation of 4‐methoxyethylbenzene, tetralin, and 2‐ethylnaphthalene with “PhI(OAc)2 + NH2SO2Me”, affording the N‐substituted methanesulfonamides in up to 56 % ee with substrate conversions of up to 34 % and amide selectivities of up to 92 %. Extension of the “complex 1 + PhI=NTs” or “complex 1 + PhI(OAc)2 + NH2R (R=Ts, Ns)” amidation protocol to a steroid resulted in diastereoselective amidation of cholesteryl acetate at the allylic C−H bonds at C‐7 with substrate conversions of up to 49 % and amide selectivities of up to 90 % (α:β ratio: up to 4.2:1). An aziridination‐ and amidation‐active chiral bis(tosylimido)ruthenium(VI) porphyrin, [Ru(Por*)(NTs)2] (3), and a ruthenium porphyrin aziridine adduct, [Ru(Por*)(CO)(TsAz)] (4, TsAz=N‐tosyl‐2‐ (4‐chlorophenyl)aziridine), have been isolated from the reaction of 2 with PhI=NTs and N‐tosyl‐2‐(4‐chlorophenyl)aziridine, respectively. The imidoruthenium porphyrin 3 could be an active species in the aziridination or amidation catalyzed by complex 2 described above. The second‐order rate constants for the reactions of 3 with styrenes, 2‐vinylnaphthalene, indene, ethylbenzenes, and 2‐ethylnaphthalene range from 3.7–42.5×10−3 dm3 mol−1 s−1. An X‐ray structure determination of complex 4 reveals an O‐ rather than N‐coordination of the aziridine axial ligand. The fact that the N‐tosylaziridine in 4 does not adopt an N‐coordination mode disfavors a concerted pathway in the aziridination by a tosylimido ruthenium porphyrin active species.

This publication has 70 references indexed in Scilit: