A Novel Counterion Effect on the Diastereoselectivity in the MnIII(salen)-Catalyzed Epoxidation of Phenyl-Substitutedcis-Alkenes

Abstract

The catalytic oxidation of the phenyl-substituted cis alkenes 1a,b by the Mn III (salen)X complexes 3a−f with iodosyl benzene (PhIO) as oxygen source affords the corresponding epoxides 2a,b in cis/trans ratios of 79:21 to 26:74. The diastereoselectivity (cis/trans ratio) depends on the counterion of the Mn III (salen)X complexes 3a−f. Thus, for the complexes 3a−c (Cl − , Br − and AcO − as ligating counterions) extensive iso-Eur.

Epoxidation studies of 2-styrylchromones using jacobsen's catalyst and hydrogen peroxide and iodosylbenzene as oxidants

“…Only a few years after this key publication an asymmetric version of this epoxidation was reported by the groups of Jacobsen [18] and Katsuki [19] using chiral Mn(III)-salen complexes as catalyst. Iodosylbenzene [17][18][19][20][21][22][23] and sodium hypochlorite [24][25][26] are the most frequently used terminal oxidants but other oxygen sources such as hydrogen peroxide [27][28][29][30], dimethyldioxirane (DMD) [31][32][33], Oxone ® [34], tetrabutylammonium monopersulfate [35], tetrabutylammonium periodate [36], mchloroperoxybenzoic acid [37] and even molecular oxygen [38] have been reported. Iodosylbenzene is a polymeric substance, prepared by base-induced hydrolysis of the commercially available iodobenzene diacetate, and the role of the catalyst in homogeneous catalysis is to solubilise it in its monomeric form.…”

Parallel mechanistic studies on the counterion effect of manganese salen and porphyrin complexes on olefin epoxidation by iodosylarenes

“…Very recently, Adam and co-workers reported a novel counterion effect on the diastereoselectivity in the epoxidation of phenyl-substituted cis-alkenes by Mn(salen)X complexes and terminal oxidants (see Fig. 1 for the structure of Mn(salen)X) [10,11]. Mn(salen)X bearing ligating counterions (e.g., X À = Cl À ) afforded trans-stilbene oxide as the major product in the epoxidation of cis-stilbene, whereas Mn(salen)X bearing nonligating counterions (e.g., X À ¼ PF À 6 ) yielded cis-stilbene oxide as the major product.…”

α-Amino cyclic dithioketal mediated asymmetric synthesis of (S)-(-)-α-(N-p-toluenesulfonyl)aminopropiophenone (N-tosyl cathinone)

“…Hydrolysis of (-)-12a (Z = Ts) with 3 afforded (S)-(-)-α-(N-tosyl)aminopropiophenone (10a) in 96% yield and better than 98% ee (Table 2, entry 9). 10 The synthesis of (S)-(-)-10a represents a formal asymmetric synthesis of (-)-cathinone (6). Interestingly, similar hydrolysis of the NBoc (-)-12b with 3 or PhI(O 2 CCF 3 ) 2 resulted in good yields of 13, but the product was racemic ( Table 2, entries 10 and 11).…”

“…7 Several targeted asymmetric syntheses of the N-tosyl and the hydrochloride salt of this material have been described because α-amino ketones are not stable unless suitably N-protected. 1 These methods include ring opening of aziridines, 8 asymmetric aminohydroxylation of silyl enol ethers and alkenes, 9 catalytic asymmetric aziridination of enols, 10 and Friedel-Crafts acylation.…”