Metal or No Metal: That Is the Question!

Abstract

alkenes · dihydroxylation · organocatalysis · oxygen heterocycles · peroxides Theoxidativefunctionalizationofalkenesisamongthemost extensively investigated synthetic transformations in organic chemistry. Simple oxidative cleavage, [1a-d] halogenation, [1e] halohydrin formation, [1f] and Wacker oxidation [1g] are widely applied in academia and industry. Moreover, transitionmetal-catalyzed epoxidation, [2a-e] dihydroxylation, [2f-h, 3] and aminohydroxylation [2i,j] reactions, for which enantioselective variants with broad scope have been developed, serve as the cornerstone of many complex-molecule syntheses.A stunning example of the progress in organocatalytic oxidation is the development of the epoxidation of alkenes with dioxiranes. Early examples with simple dimethyldioxirane generated from acetone (1) and Oxone (potassium peroxymonosulfate) in situ were reported in 1979 by Edwards et al., [4a] and the scope of the reaction was expanded by Curci et al. in 1980.[4b] The same group developed the first asymmetric epoxidation in 1984 with dioxiranes derived from chiral ketones 2 and 3;[4c] however, only low asymmetric induction could be achieved at this time (Figure 1). Quite a number of other chiral ketones were subsequently investigated [4d,e] to improve the enantiomeric excess until in 1996 the readily available fructose-derived ketone 4 was introduced by Shi et al.[4f] While stoichiometric amounts of 4 were initially necessary to achieve high enantioselectivity, only one year later the same group was able to establish a catalytic variant by adjusting the pH of the reaction;[4g] under these conditions the reaction rivalled the efficiency of metalbased asymmetric epoxidations (Scheme 1).Another class of organic compounds, organic acyl peroxides, could potentially break the dominance of metalcatalyzed processes for the oxidative functionalization of alkenes. So far, the primary oxidant OsO 4 is still the reagent of choice for the syn dihydroxylation of alkenes [2f-h, 3] for both asymmetric and non-asymmetric metal-catalyzed reactions.

Metal-free syn-dioxygenation of alkenes

“…A promising area is the use of cyclic diacyl peroxides and in particular malonoyl peroxides. 3 Cyclopropyl malonoyl peroxide 3 has been shown to be an effective reagent for the syn-dihydroxylation of a series of stabilised alkenes containing a wide range of functionality (22 examples) (Scheme 1). 4 Treatment of an alkene with just 1.2 equivalents of peroxide 3 in the presence of 1 equivalent of water followed by basic hydrolysis leads to the corresponding syn-diol in excellent yield and very high levels of diastereoselectivity.…”

C−O coupling of Malonyl Peroxides with Enol Ethers via [5+2] Cycloaddition: Non‐Rubottom Oxidation

“…[1] Recently we reported efficient methods for oxidative CÀ O coupling of β-dicarbonyl [2] and Nheterocyclic [3] compounds with diacyl peroxides, in which one of the reagents, diacyl peroxide, acts both as an O-component and as an oxidizing agent. Cyclic diacyl peroxides firstly prepared in the 1950 s [4] were rediscovered a few years ago, [5] when previously practically unavailable reactions stereoselective syn- [6] and anti-dihydroxylation [7] of alkenes, arene oxidation, [8] alkene oxyamination, [9] and dioxygenation, [10] Hofmann-Löffler-Freytag-type reaction, [11] selective sulfide oxidation, [12] peracids formation, [13] ring opening/halogenation of cycloalkanols, [14] and the [3 + 2] cycloaddition of arynes to azides [15] were realized. High oxidative ability, cyclic structure and absence of an acidic proton attached to the peroxide group favorably differ malonyl peroxides from related oxidants -peracids and noncyclic diacyl peroxides.…”

“…[44] In regard to the oxyfunctionalization of carbonyl targets, [45] they were previously limited to the alkoxy, [46] peroxy, [47] oxygensulfonyl, [48] oxygen-phosphoryl, [49] aminoxy [50] groups. In a few studies α-acyloxy-carbonyl products were synthesized using Cu/CuI/air, [51] Cu(acac) 2 /TBHP, [52] CuI/O 2 , [53] Pybox-Cu(II) complex/K 4 [Fe(CN) 6 ], [54] TBAI/H 2 O 2 [55] or TBAI/TBHP, [56] hypervalent iodine compounds, [57] N-methyl-O-benzoylhydroxylamine hydrochloride, [58] or TBAI/electric current. [59] Apart from these reports, α-oxygenation of mono-carbonyl compounds were achieved by hydroxylation [60] and alkoxylation [61] of silyl enol ethers, hydroxylation [62] and alkoxylation [61c,63] of alkyl enol ethers or enolates.…”

Oxidation of dimethylplatinum(II) complexes with malonyl peroxide derivatives

“…In addition, the peroxide derivatives phthaloyl peroxide (PP), CBMP, and CPMP (Chart 1) are useful reagents for metal-free dihydroxylation of alkenes, with the reactivity sequence CBMP > CPMP > PP reflecting the degree of ring strain in the compounds. [45][46][47][48] …”