C acetoxylation

Aryllead(rv) triacetates react with phenols to give mainly products of ortho-C-arylation, formed by ligand coupling mechanisms.45 4511 65 In an attempt to extend the arylation of polymethylbenzenes to phenolic substrates, Pinhey et al. treated mesitol 30 with /(-rncthoxy phenyl lead triacetate 1 in CHCI3 (Equation (37)). The reaction afforded a mixture of the C-arylated products 31 and 32 together with minor amounts of the C-acetoxylated product 33 and O-aryl ether 34.45 45a... 

Analysis of the NMR spectra of heteratisine and its derivatives at lower field than the methoxyl resonance, in conjunction with biogenetic analogies, permits location of the lactone, the tertiary hydroxyl, and, with some reservations, the methoxyl group (151). The splitting of the H—C acetoxyl signal in heteratisine acetate (CCCXCVI) and oxoheteratisine acetate (CCCXCVIII) into a doublet of doublets is consistent with its location at C-6 and spin coupling to H(C-7) and H(C-5). 

H)-Cinnolinone (67, R = H) with lead tetracetacte in acetic acid did not imdergo O- or 7V-acetylation but oxidative C-acetoxylation to afford... 

TABLE 5.4 Yields moles %) in the nitration and acetoxylation of some derivatives of benzene at 25 °C... 

Expts. 16, //. Pure nitric acid was used. In expt. 16 the reaction was of the first order in the concentration of the aromatic, and of half-life 1-1-5 minutes (similar to that of toluene under the same conditions). In expt. 17 the sodium nitrate slowed the reaction (half-life c. 60 min). About 2 % of an acetoxylated product was formed (table 5-4). 

In the first step of the reaction, the acetoxylation of propylene is carried out in the gas phase, using soHd catalyst containing pahadium as the main catalyst at 160—180°C and 0.49—0.98 MPa (70—140 psi). Components from the reactor are separated into Hquid components and gas components. The Hquid components containing the product, ahyl acetate, are sent to the hydrolysis process. The gas components contain unreacted gases and CO2. After removal of CO2, the unreacted gases, are recycled to the reactor. In the second step, the hydrolysis, which is an equhibrium reaction of ahyl acetate, an acid catalyst is used. To simplify the process, a sohd acid catalyst such as ion-exchange resin is used, and the reaction is carried out at the fixed-bed Hquid phase. The reaction takes place under the mild condition of 60—80°C and ahyl alcohol is selectively produced in almost 100% yield. Acetic acid recovered from the... 

Electrophilic addition to quinones, eg, the reaction of 2-chloro-l,4-ben2oquinones with dia2onium salts, represents a marked contrast with acetoxylation in product distribution (58). Phenyldia2onium chloride (Ar = C H ) yields 8% 2,3-substitution [80632-59-3] 75% 2,5-substitution [39171-11-4] and 17% 2,6-substitution [80632-60-6]. Fory)-chlorophenyldia2onium chloride, the pattern is 28% 2,3-substitution [80632-61-7], 35%... 

An acetoxyl group at C-21, if present, is retained and an a,) -unsaturated ketone system in ring A does not interfere. 

A direct method for introduction of a C-21 acetoxyl group into a 20-keto-pregnane is by reaction with lead tetraacetate at room temperature. Although originally the reaction carried out in hot acetic acid gave low yields, a careful study by Henbest has defined conditions so that yields as high as 86 % can be obtained at room temperature. The preferred solvent is 5 % methanol in benzene, with boron trifluoride etherate as catalyst. With either methanol or benzene, the yield is less than 4%. 

Esters and acetylated hydroxyl groups are completely stable under the experimental conditions, but with ketals 10 29,110,112 yields are generally observed in the thermal reaction. Double bonds do not seem to interfere seriously with the course of the reaction provided that the geometric relationship of the free hydroxyl group to the angular methyl group is not changed drastically. In some cases allylic acetoxylation occurs, e.g., at C-7 of A -steroids. ° Ketones are usually stable (especially under photo-lytic conditions) but occasionally a-acetoxylation has been observed. 

Cephachlor (35) became accessible when methods for the preparation of C-3 methylenecephalosporins became convenient. The allylic C-3-acetoxyl residue characteristic of the natural cephalosporins is activated toward displacement by a number of oxygen- and sulfur-containing nucleophiles. Molecules such as can therefore be prepared readily. Subsequent reduction with chromium(II) salts leads to the desired C-3... 

The first step is the liquid phase addition of acetic acid to butadiene. The acetoxylation reaction occurs at approximately 80°C and 27 atmospheres over a Pd-Te catalyst system. The reaction favors the 1,4-addition product (l,4-diacetoxy-2-butene). Hydrogenation of diacetoxybutene at 80°C and 60 atmospheres over a Ni/Zn catalyst yields 1,4-diacetoxybu-tane. The latter compound is hydrolyzed to 1,4-butanediol and acetic acid ... 

Epimerization of 4 at C-2 provided 5a-carba-a-DL-galactopyranose (6). When the pentaacetate IS was heated in acetic acid containing sulfuric acid, epimerization occurred at C-2 through an intermediary cyclic acetoxonium ion (18), with anchimeric assistance of the vicinal, axial acetoxyl group. After acetylation, 5a-carba-a-DL-galactopyranose pentaacetate (19) was obtained in a yield of 14% it was converted into 6 by hydrolysis. The antimicrobial activity of the racemate 6 was found to be about half that of the natural antibiotic 7 in the same assay system, indicating that the L-antipode is probably inactive. " ... 

Then the synthetic 32 was converted to the cyanoglucoside sutherlandin (44) which was isolated from leaves of Acacia sutherlandii. Acetylation of a diastereomeric mixture of 32 gave the corresponding acetate which was subjected to the hydrogenation and the subsequent oxidation to yield the a-acetoxyl ketone (45, 84% overall yield from the acetate of 32). The Homer-Emmons reaction of 45 using diethyl cyanomethylphosphonate furnished (Z)-46a (33% yield from 45) and ( )-46b (31% yield from 45). Deprotection of the presumably desired (Z)-46a afforded (Z)-44 (76% yield), whose C-NMR spectra were identical with those of the natural sutherlandin (44) (Fig. 6). 

The synthesis in Scheme 13.41 is also built on the desymmetrization concept but uses a very different intermediate. cA-5,7-Dimethylcycloheptadiene was acetoxylated with Pd(OAc)2 and the resulting all-cA-diacetate intermediate was enantioselectively hydrolyzed with a lipase to give a monoacetate that was protected as the TBDMS ether. An anti Sw2 displacement by dimethyl cuprate established the correct configuration of the C(2) methyl substituent. Oxidative ring cleavage and lactonization gave the final product. 

P2j Z = 2 Dx = 1.363 R = 0.051 for 982 intensities. The lactone has the3T4 conformation, withQ = 13 pm, (p = 337°, andaC-2-C-3-C-4-O torsion-angle of — 120. Both the equatorial and the axial acetoxyl groups have their planes approximately normal to that of the lactone ring. 

Hydroxyprotoberberine 59a and ( )-corytencine (98) led to 13-acetoxy compounds 104,105, and 107 moreover, the 2,3,9,10,12-pentaoxy-genated protoberberine 108 was also obtained from 98 via the p-quinol acetate 106 through a retro-Mannich reaction followed by recyclization (74,75). Oxidation in dichloromethane instead of acetic acid proceeded differently, namely, 97 and 98 led to pentaoxygenated protoberberines 103 and 109 by introduction of an acetoxyl group at C-4 and C-12, respectively, via o-quinol acetates (76). 

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