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Acetoxylation of ketones

Lactams, by Beckmann rearrangement, 343 Lactols, 402 Lactones, 346-349, 397 Lanosterol, 401, 408 Lead tetraacetate, acetoxylation of enol derivatives, 184 —, acetoxylation of ketones, 176-177... [Pg.242]

Although acetoxylation of ketones with lead tetraacetate and with mercuric acetate generally afford the same product, Zalkow " reports that pulegone reacts with the former reagent to give an epimeric mixture of 4-acetoxy derivatives and with the latter to give a 2-acetoxy epimer mixture. [Pg.274]

In 2005 Ochiai and coworkers reported the first iodobenzene-catalyzed reaction, a catalytic variant of a-acetoxylation of ketones based on the in situ generation of (diacetoxyiodo)benzene from iodobenzene using m-chloroperoxybenzoic acid (mCPBA) as a terminal oxidant [3]. In a typical example, the oxidation of a ketone with mCPBA (2 equiv) in acetic acid in the presence of a catalytic amount of iodobenzene (0.1 equiv), BF3 -OEt2 (3 equiv) and water (5 equiv) at room temperature under argon affords the respective a-acetoxy-ketone 1 in a moderate yield (Scheme 4.1). 4-Iodotoluene and 4-chloroiodobenzene can also serve as catalysts in the a-acetoxylation of ketones under these reaction conditions however, the use of iodobenzene results in the highest yields [3]. The use of at least 10 mol% iodobenzene in this reaction is necessary. When smaller amounts are used, the reaction slows and Baeyer-Villiger oxidation products resulting from a direct reaction of mCPBA and the ketone are observed [3],... [Pg.338]

Based on Ochiai s procedure for a-acetoxylation of ketones, Ishihara and coworkers have developed the hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones [18], Optimized reaction conditions consist of the treatment of a ketocarboxylic acid with iodobenzene (10 mol%), p-toluenesulfonic acid monohydrate (20 mol%) and mCPBA as a stoichiometric oxidant in nitromethane solution Scheme 4.3 shows as a representative example the cyclization of ketocarboxylic acid 4 to ketolactone 5. [Pg.339]

Charette and coworkers have developed tetraarylphosphonium (TAP)-supported (diacetoxyiodo)benzene 109 (Figure 5.5), which can be used as a recyclable reagent or a catalyst for the a-acetoxylation of ketones [101]. Similarly to the imidazolium-supported [bis(acyloxy)iodo]arene 99, the reduced form of the TAP-supported reagent 109 can be recovered from the reaction mixture by simple filtration after treatment with ether. [Pg.401]

M. Ochiai, Y. Takeuchi, T. Katayama, T. Sueda, K. Miyamoto, lodobenzene-catalyzed a-acetoxylation of ketones, in situ generation of hypervalent (diacyloxyiodo)benzenes using ra-chloroperbenzoic acid, J. Am. Ghem. Soc. 127 (2005) 12244—12245. [Pg.375]

In 1960, Moiseev and coworkers reported that benzoquinone (BQ) serves as an effective stoichiometric oxidant in the Pd-catalyzed acetoxylation of ethylene (Eq. 2) [19,20]. This result coincided with the independent development of the Wacker process (Eq. 1, Scheme 1) [Ij. Subsequently, BQ was found to be effective in a wide range of Pd-catalyzed oxidation reactions. Eor example, BQ was used to achieve Wacker-type oxidation of terminal alkenes to methyl ketones in aqueous DMF (Eq. 3 [21]), dehydrogenation of cyclohexanone (Eq. 4 [22]), and alcohol oxidation (Eq. 5 [23]). In the final example, 1,4-naphthoquinone (NQ) was used as the stoichiometric oxidant. [Pg.80]

These multicomponent catalyst systems have been employed in a variety of aerobic oxidation reactions [27]. For example, use of the Co(salophen) cocatalyst, 1, enables selective allylic acetoxylation of cyclic alkenes (Eq. 6). Cyclo-hexadiene undergoes diacetoxylation under mild conditions with Co(TPP), 2 (Eq. 7), and terminal alkenes are oxidized to the corresponding methyl ketones with Fe(Pc), 3, as the cocatalyst (Eq. 8). [Pg.81]

In fact, the role of copper and oxygen in the Wacker Process is certainly more complicated than indicated in equations (151) and (152) and in Scheme 10, and could be similar to that previously discussed for the rhodium/copper-catalyzed ketonization of terminal alkenes. Hosokawa and coworkers have recently studied the Wacker-type asymmetric intramolecular oxidative cyclization of irons-2-(2-butenyl)phenol (132) by 02 in the presence of (+)-(3,2,10-i -pinene)palladium(II) acetate (133) and Cu(OAc)2 (equation 156).413 It has been shown that the chiral pinanyl ligand is retained by palladium throughout the reaction, and therefore it is suggested that the active catalyst consists of copper and palladium linked by an acetate bridge. The role of copper would be to act as an oxygen carrier capable of rapidly reoxidizing palladium hydride into a hydroperoxide species (equation 157).413 Such a process is also likely to occur in the palladium-catalyzed acetoxylation of alkenes (see Section 61.3.4.3). [Pg.365]

These and related reactions of lead tetraacetate have been widely used in synthetic organic chemistry, and are the subject of several reviews.6-10 However, they have found relatively few applications in the carbohydrate field specifically. One important application has been the synthesis of ketones by way of acetoxylation of suitable unsaturated compounds. By treating 1,2-0-isopropylidene-2-propene-l, 2-diol (I) in benzene at 50° with... [Pg.10]

Acetophenones, aliphatic and cyclic ketones were a-acetoxylated by DIB in acetic acid-acetic anhydride, in the presence of sulphuric acid, in moderate yield some / -diketones were similarly acetoxylated at the methylene carbon. The more reactive trimethylsilyl ethers reacted at room temperature without acid catalysis, with retention of their silyl group the products came either from substitution of the vinylic hydrogen or from bis acetoxylation of the double bond. [Pg.20]

The cyclic vinyl ether (182),170 postulated last year as an intermediate in the 21-acetoxylation of the hemiacetal (183), can be prepared in good yield by heating the hemiacetal with aluminium isopropoxide in toluene under argon, followed by direct chromatography on basic alumina.171 The vinyl ether was converted into the 20,21-diol (184) either by reaction with osmium tetroxide or by acetoxylation with lead tetra-acetate, followed by hydrolysis. The hypoiodite reaction, followed by oxidation, allows direct conversion of a 21-acetoxypregnan-20/3-ol (185) into the 18-iodo-20-ketone (186), which is solvolysed in the presence of silver acetate to provide a new route to the 21-acetate of 18-hydroxydeoxycorticosterone hemiacetal (187).171... [Pg.251]

Numerous examples are available that demonstrate the utility of the process. Sasaki and Eguchi utilized LTA to effect a-acetoxylation of isodihydro-0 acetylisophotosantonic lactone (1). This oxidation is both chemoselective towards the ketone and regioselective towards the less substituted position... [Pg.153]

Some other reactions involving oxidation of the C—Hg bond have been known for some time, but these are either of limited synthetic appeal or have experienced no significant development in recent years. Thus ozonolysis of the C—Hg bond to form carboxylic acids or ketones falls into the first category, whereas allylic acetoxylation of alkenes by Hg(OAc>2 falls into the second category. Nevertheless, this allylic oxidation (Treibe s reaction) has considerable synthetic utility, and has been reviewed quite recently.5 ... [Pg.637]

The anodic a-acetoxylation or a-methoxylation of ketones has been shown to be a powerful tool for the 1,2-transposition of the caibonyl group. The overall process is described by equation (24). ... [Pg.798]

Reaction of ketones with LTA in benzene in the presence of boron trifluoride etherate at or below room temperature effects rapid a-acetoxylation." The yields are indeed improved in most cases, for... [Pg.153]

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. [Pg.17]

Electrochemical a-acetoxylation of octyl phenyl sulfide, methyl octyl sulfide, and several a-sulfanylated esters and ketones was achieved in HOAc-NaOAc solutions at Pt electrodes using high concentrations of the sulfur compounds [103]. Phenylthio derivatives produce a single a-acetoxy compound, whereas with the methylthio compounds two regioisomers are formed [Eqs. (55)-(56)]. [Pg.639]

Related acetoxylatiom. Iffland found that lead tetraacetate oxidizes ketoximes (I) smoothly to nitrosoacetates (III). The Henbest mechanism cited above for acetoxylation of a ketone (7 10) suggests the intermediate II and the transition... [Pg.274]

Compounds presenting the possibility of keto-enol tautomerism react easily with lead tetraacetate to afford products of a-acetoxylation. This reaction is found in the case of ketones and phenols, although it is frequently accompanied by other products derived from alternate mechanistic pathways. [Pg.205]

The reaction of enamines with aryllead (IV) triacetates presents some similarities with their reaction with lead (IV) tetraacetate. The enamines of aldehydes do not react, and the enamines of ketones undergo an exothermic reaction to afford moderate to good yields of a-arylketones. When the ring size or the steric hindrance in the vicinity of the double bond increases, the yield falls significantly, and a-acetoxylation becomes a major competing pathway. [Pg.229]


See other pages where Acetoxylation of ketones is mentioned: [Pg.154]    [Pg.154]    [Pg.249]    [Pg.1754]    [Pg.205]    [Pg.332]    [Pg.154]    [Pg.154]    [Pg.249]    [Pg.1754]    [Pg.205]    [Pg.332]    [Pg.38]    [Pg.74]    [Pg.406]    [Pg.26]    [Pg.528]    [Pg.361]    [Pg.1043]    [Pg.153]    [Pg.170]    [Pg.153]    [Pg.170]    [Pg.361]    [Pg.267]    [Pg.983]    [Pg.1004]   
See also in sourсe #XX -- [ Pg.44 , Pg.177 , Pg.442 ]




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