F-Butyl perbenzoate

The allylic position of olefins is subject to attack by free radicals with the consequent formation of stable allylic free radicals. This fact is utilized in many substitution reactions at the allylic position (cf. Chapter 6, Section III). The procedure given here employs f-butyl perbenzoate, which reacts with cuprous ion to liberate /-butoxy radical, the chain reaction initiator. The outcome of the reaction, which has general applicability, is the introduction of a benzoyloxy group in the allylic position. 

In 1959, Kharasch et al.43 reported an allylic oxyacylation of olefins. In the presence of f-butyl perbenzoate and a catalytic amount of copper salt in refluxing benzene, olefin was oxidized to allyl benzoate, which could then be converted to an allyl alcohol upon hydrolysis. It is desirable to introduce asymmetric induction into this allylic oxyacylation because allylic oxyacylation holds great potential for nonracemic allyl alcohol synthesis. Furthermore, this reaction can be regarded as a good supplement to other asymmetric olefinic reactions such as epoxidation and dihydroxylation. 

A method for determination of various types of peroxides consists of RP-HPLC separation and applying post-column UV radiation to convert the peroxide to H2O2, which may be determined by CLD with bis(2,4,6-trichlorophenyl) oxalate (140) in the presence of 2,4,6,8-tetrathiomorpholinopyrimido[5,4-(J]pyrimidine (194) as fluorescence enhancer. Dibenzoyl peroxide and f-butyl perbenzoate have LOD (SNR 3) 6.8 and 7.5 p.M, respectively, and linearity range from 40 to 400 p.M. The method was applied for determination of dibenzoyl peroxide used as whitener of wheat flour, after extraction with ethanol . See a similar method in Section VLB.3. 

A three-step method can be applied for analysis of mixtures of hydroperoxides and peroxides, consisting of RP-HPLC separation, photolytic conversion of the emerging analyte to H2O2, by irradiation with a 254 nm UV lamp and application of the fluorometric technique depicted in equation 34 (w = 1) to determine this analyte, f-Butyl perbenzoate has LOD 0.3 mgL , linearity range 0.9-80 mgL and RSD 6.1% . See a similar method in Section VI.B.l. 

Silver acetate has a small catalytic effect on the alkene substitution reaction but 5 equiv. of the salt only give 140% of stilbene in the styrene phenylation, based upon palladium.15 The same reaction carried out at 80 C under 300 lbf in-2 (1 lbf in-2 = 6.89 kPa) of oxygen gives stilbene in 248% yield, based upon palladium.16 The best reoxidation reagent is f-butyl perbenzoate, which yields 10-14 turnovers of the palladium in the vinyl substitution of cinnamaldehyde and similar alkenes with benzene.17... 

Reaction with ethers. Decomposition of f-butyl perbenzoate by cuprous chloride in the presence of an ether, (RCH2)20, and an alcohol, R OH, leads to the acetal, RCH(0R )2. ... 

Fig. 1. Oxidation of mixtures of cumene and aralkyl hydrocarbons at 90°C, 0.02 M f-butyl perbenzoate. A, Dibenzyl ether B, indan C, diphenylmethane D, ethylbenzene E, theoretical for an inert diluent. Reprinted with permission from ref. 139. Copyright by the American Chemical Society.

The use of thienyl Grignard reagents, and more recently lithiated thiophenes, has been extensive and can be illustrated by citing formation of oxythiophenes, either by reaction of the former with f-butyl perbenzoate or the latter directly with bis(trimethylsilyl) peroxide or via the boronic acid, the synthesis of thiophene carboxylic acids by reaction of the organometallic with carbon dioxide, the synthesis of ketones, by reaction with a nitrile, or alcohols by reaction with aldehydes, by the reaction of 2-lithiothiophene with A -tosylaziridine, and by syntheses of thieno[3,2- ]thiophene and of dithieno[3,2- 2, 3 - /]thiophene. Some of these are illustrated below. 

OXIDATION, REAGENTS Acetyl nitrate. Bis(tri-n-butyltin)oxide. Bromine-Hexameth-ylphosphoric triamide. f-Butyl perbenzoate. Ceric ammonium nitrate. N-chlorosuc-cinimide-Dimethyl sulfide. Chromic add. Chromic anhydride. Chromic anhydride-Acetic anhydride. Chromic anhydride-Hexamethylphosphoric triamide. 2,3-Dichloro-5,6-dicyano-l,4-benzoquinone. Dimethyl sulfoxide. Dimethyl sulfoxide-Trifluoro-acetic anhydride. Diphenylseleninlc anhydride. Iodine tris(trifluoroacetate). Lead tetraacetate. N-Methylmorpholine -N-oxide. p-NitrobenzenesulfonyI peroxide. Oxygen, singlet. Palladlumfll) chloride. Peroxybcnzimidic acid. Phenylseleninyl chloride. N-Phenyl-l,2,4-triazoline-3,5-dione. Potassium chromate. Potassium superoxide. Pyri-dinium chlorodiromate. Salcomine. Silver carbonate-Celite. Sodium hypochlorite. Sulfuryl chloridc-Silica gel. Thallium(III) acetate. ThaUium(III) nitrate. Triphenyl phosphite ozonide. Trltyl tetrafluoroborate. Uranium hexafluoride. 

Allylic Oxidation. Chiral CuOTf-bis(oxazoline) complexes catalyze the asymmetric Kharasch acyloxylation of cyclopentene, cyclohexene, and cycloheptene with f-butyl perbenzoate with good yields but moderate enantioselectivities (eq 125). ... 

Replacement of f-butyl perbenzoate in the oxidation reaction by f-butyl hydroperoxide allows, in the presence of catalytic CuOTf-bis(oxazoline) complex, allylic peroxidation of cyclohexene (eq 127). While the yield is good (75%), the enantioselectivity is quite poor (9% ee). A similar trend (high yield, low ee) is observed for the peroxidation of cyclopentene, a-angelica lactone and allylbenzene. 

Martin and his co-workers have provided a firm experimental foundation for anchimeric assistance in the homolytic decomposition of per-benzoate derivatives (Table 6). A single o-phenylthio group was found to increase the rate of decomposition of f-butyl perbenzoate by a factor of ca. 45 thousand. The effect is not steric since an o-r-butyl group hardly affects the rate of perester decomposition [compare (95) versus (99), Table 6]. A noticeable but weak effect is observed with the homologous sulfide (96). In addition to sulfur, anchimeric assistance by iodine and vinyl groups in (97) and (98), respectively, was observed. The bridged canonical species... 

Preparative Methods can be most conveniently synthesized from commercially available vinyltrimethylsilane (1) (eq 1). Radical addition of sodium bisulfite to the vinyl group catalyzed by f-butyl perbenzoate yields the sulfonate salt (2) which can be directly converted to SESCl (3) with phospho-rus(V) chloride. The chloride (3) can then be purified by distillation. The intermediate sulfonate salt (2) is commercially available. The chloride (3) can also be prepared in 62% yield from the salt (2) using sulfuryl chloride and triphenylphosphine (eq 2) A less convenient procedure to synthesize SESCl (3) using /3-trimethylsilylethylmagnesiumchloride (4) and sulfuryl chloride has also been developed (eq 3). ... 

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