Lactonizations manganese acetate

Manganese acetate-promoted oxidative addition of 1,3-dicarbonyl compounds (351) to endo-cyclic enol ethers (352) and enol lactones (353) gives 2,3,3a,6a-tetrahydrofuro[2,3-6]furan derivatives (354) and (355) <87CL223, 91TL711, 91TL7107). 

Manganic acetate (manganese triacetate), Mn(OCOCH3)3, is prepared by refluxing a solution of manganese acetate tetrahydrate in acetic acid with potassium permanganate [S03]. This oxidant hydroxylates ben-zylic methylene groups [416] and forms lactones from terminal alkenes [803, 804] (see equation 88). 

Among the preferred and also first oxidants to be used for this purpose was manganese(III) acetate in acetic acid, for which the formula Mn30(0Ac)7 might be appropriate53,87. Oxidation of acetic acid, for example, leads to radical 54 which, upon addition to butadiene and oxidation of the adduct radical, leads to /-lactone 55 (equation 24). 

The low yield in this reaction might be caused by a number of reasons. First, the overall reaction is only rapid for readily enolizable compounds. 1,3-Dicarbonyl compounds will therefore be a better choice as compared to acetic acid. Second, to prevent oxidation of radical 54, it is advantageous to work with excess diene and therefore speed up trapping of 54 through diene addition. Finally, lactone 55 can, as an enolizable compound itself, also be oxidized by manganese(III) acetate and form various oxidation products. Shorter reaction time and the use of understoichiometric amounts of oxidant might therefore benefit the overall result. All these factors have been taken into account in the synthesis of bicyclic /-lactone 56, which has been obtained from cyanoacetic acid and 1,3-cyclohexadiene in 78% yield within 15 min reaction time (equation 25)60,88. 

Manganese(lll) acetate oxidation of (+)-p-menth-l-ene yields the two lactones (165 X=0, Y = CH2) and (165 X = CH2, Y = O) as major products together with anticipated acetates similar oxidation of (+)-pulegone yields the C-2 acetates in low yield and oxidation of isomenthone in the presence of isopropenyl acetate results in acetonylation at C-2 and C-4. Further examples of the rearrangement of epoxides with KOBu -aprotic solvents (pyridine is favoured) have been reported (c/. Vol. 6, p. 44), e.g. (166) to (167), although with the corresponding 1,2-epoxy-... 

Manganese(lil) acetate oxidation of a-pinene yields two lactones analogous to those reported earlier with (+)-p-menth-l-ene however, the major product consists of derived acetates [of a-terpineol, c/5-pin-3-en-2-ol, and myrtenol (224 ... 

Olefins react with manganese(III) acetate to give 7-lactones.824 The mechanism is probably free-radical, involving addition of CH2COOH to the double bond. Lactone formation has also been accomplished by treatment of olefins with lead tetraacetate,825 with a-bromo carboxylic acids in the presence of benzoyl peroxide as catalyst,826 and with dialkyl malonates and iron(III) perchlorate Fe(C104)3-9H20.827 Olefins can also be converted to 7-lactones by indirect routes.828 OS VII, 400. 

It should be noted that nonmetallic redox reactions also experience the sonication influence. The preparation of y-lactons from olefines upon manganese triacetate oxidation is an example. The reaction with monomethyl malonate in acetic acid, which does not occur at 0-10°C, proceeds smoothly when sonication is applied (Allegretti et al. 1993). From cyclohexene, only the cis ring fusion in the bicyclic lactone is observed the product is formed at 80% yield for 15 min at 10°C. The overall scheme of the reaction, without the detailed mechanism is shown in Scheme 8-18. 

The manganese(UI) acetate mediated oxidative cyclization of fl-ketoesters has been utilized to construct a pentacyclic compound in low yield [95CC403]. The intermediate radical 107 formed from an initial 6-endo-trig reaction undergoes further lactonization in the presence of copper(II) acetate. The compound 108 has the basic skeleton found in fungal metabolite sesquiterpene phenols. 

The oxidation of olefins by manganese (III) acetate in acetic acid219-221 resulted in the formation of 7-lactones,... 

Polycyclic y-lactones. An intramolecular version of the formation of y-lactones by reaction of an alkene with acetic acid and manganese(HI) acetate (1) (6, 355-356) provides a general route to polycyclic y-lactones. Thus the unsaturated p-keto acid 2 cyclizes to the ds-bicyclic y-lactone 3 when warmed in acetic acid with 1 (1.3 equiv.)2... 

Acetates of tin, lead, manganese, antimony, and zinc as well as esters of orthotitanates catalyze the reactions Optimum temperatures for these reactions are between 230-260 C at 0.03-1 mm Hg pressure. Block copolymers can also form by ring-opening polymerizations of lactones, when carboxy-terminated macromolecular initiators are used" ... 

Other notable reports of annulations involving nitriles were concerned with the preparation of y-lactones prepared from cyano-acetic acid derivatives and olefins in the presence of manganese(III) acetate.The "carbon-zip" ring expansion of... 

The isolation of saturated and unsaturated acetic acid derivatives in the manganese(m) acetate oxidation of olefins has been reported earlier examples of this oxidation led solely to y-lactones. A one-step synthesis of aeo-di-carboxylic acid diesters has been reported, based on Kolbe electrolysis of oxalic and malonic half-esters in the presence of olefins, and is exemplified in Scheme 2. As part of a study of insect hormone activity, Kolbe electrolysis has been utilized in the preparation of aj9-unsaturated Cj4—Cj7 acid esters with a terminal quaternary alkyl group. The utility of liquid hydrogen fluoride in the Koch carbonylation of olefins has been descried, as has a general study of this reaction. ... 

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