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.
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) + NH(2)SO(2)Me", 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) + NH(2)R (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 % (alpha:beta 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 3.7-42.5x10(-3) dm(3) 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.
Liang
Jiang-Lin
JL
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Huang
Jie-Sheng
JS
Yu
Xiao-Qi
XQ
Zhu
Nianyong
N
Che
Chi-Ming
CM
D000475:Alkenes / Q000737:chemistry*; D000577:Amides / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D007700:Kinetics; D017895:Manganese Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010084:Oxidation-Reduction; D017975:Ruthenium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D000577:Amides; D017895:Manganese Compounds; D008665:Metalloporphyrins; D017975:Ruthenium Compounds; D009584:Nitrogen