Aziridination of alkenes catalysed by porphyrinirons: selection of catalysts for optimal efficiency and stereospecificity

Abstract

meso -Tetraary I porp hyri n i ron (I 11) derivatives cata lyse t he Ntosylaziridi nation of aryl -su bst ituted styrenes by tosylimidoiodobenzene, PhlNTs, a nitrogen analogue of iodosylbenzene. Three secondary reactions were found to limit the yield of N-tosylaziridination: (i) the formation of toluene-psulphonamide, TsN H2, which is presumably derived from hydrolysis of a possible iron-nitrene, Fe=NTs, intermediate, (ii) the conversion of the Fe(TPP) (CI) (TPP = tetraphenylporphyrin) catalyst into an iron(ii1) complex where the NTs moiety is inserted into an iron-nitrogen bond of Fe(TPP) (CI), (iii) an oxidative degradation of the porphyrin catalyst. These secondary reactions were avoided to a great extent by using anhydrous conditions and Fe(TDCPP)(CIO,) (TDCPP = tetrakis-2,6-dichlorophenylporphyrin) as a catalyst instead of Fe(TPP) (CI) and Fe(TPP) (CIO,). Under these conditions, N-tosylaziridination of styrene, cis-and trans-stilbene, and 1 ,I -diphenylethylene was performed with yields between 40 and 90%. Fe(TDCPP)(CIO,) was also found to be the best catalyst for N-tosylaziridination of aliphatic alkenes such as hex-I -ene, cyclo-octene, and cis-and trans-hex-2-enes. Although N-tosylaziridination of the two latter alkenes catalysed by Fe(TPP) (CI) was not stereospecific, this reaction became stereospecific with Fe(TDCPP) (CIO,) as catalyst. These results show that by a proper choice of the porphyriniron catalyst, relatively good yields of Ntosylaziridination of alkenes by PhlNTs can be obtained. As for 1,2-disubstituted aliphatic alkenes, syn addition of the NTs moiety to the double bond takes place. A possible mechanism is presented.

Rhodium(II)‐Catalyzed Oxidative Amination

“…The preponderance of mechanistic data collected with these systems strongly implicates a radical abstraction/rebound mechanism for C-N bond formation [22,27]. Such findings contrast with the work of Müller for analogous reactions using rhodium catalysts.…”

“…Additional studies established the viability of manganese(III)-and iron(III) porphyrin complexes as promoters for intermolecular C-H amination reactions with p-CH 3 C 6 H 4 SO 2 N=IPh (TsN=IPh) and simple hydrocarbon substrates such as 2-hexene (Scheme 17.3) [20][21][22]. In these experiments stereospecific oxidation was not observed, and a mechanism involving C-H abstraction by a high-valent manganese intermediate followed by rapid trapping of the incipient radical (radical rebound) was inferred (Scheme 17.4) [22,27]. Such findings contrast with rhodium-catalyzed reactions of ArSO 2 N=IPh in which a metallo-nitrene mechanism is thought to be operative (vide infra).…”

Copper(ii) complexes incorporating poly/perfluorinated alkoxyaluminate-type weakly coordinating anions: Syntheses, characterization and catalytic application in stereoselective olefin aziridination

“…Previous investigations by Mansuy, 28 Evans, 20b Jacobsen 29 and Che 16a indicate that the mechanism is system dependent both respect to the metals, the ligands and on the nature of the counteranions. Previous investigations by Mansuy, 28 Evans, 20b Jacobsen 29 and Che 16a indicate that the mechanism is system dependent both respect to the metals, the ligands and on the nature of the counteranions.…”

Rhodium(II)‐Catalyzed CH Insertions with {[(4‐Nitrophenyl)sulfonyl]imino}phenyl‐λ3‐iodane

“…An exception to this is the transfer of sulfonylnitrene from TsN=IPh (phenyl[(tosylsulfonyl)imino]-i13-iodane = [4-methylbenzenesulfonamidato(2 -)-Nlphenyliodide) [4]. Mansuy et al reported the aziridination of olefins with TsN=IPh in the presence of Fe"' and Mn"' porphyrinates [5], and subsequently, Evans et ul. described an enantioselective aziridination of olefins using TsN=IPh and chiral Cu' catalysts [6].…”