Methyl acetate cleavage

This new procedure is especially valuable in the synthesis of benzoxazinones bearing one or two methoxy substituents or a 6,7-methylenedioxy unit at the aromatic ring. A drawback of the former methyl acetal cleavage method (Fig. (7), [110]) consisted in an insufficient selectivity of the boron trichloride mediated 2-methoxy group... 

Ultraviolet irradiation of oxadiazoline (38d) at 333.6 nm (or irradiation using benzophenone as a triplet sensitiser) gave 2-diazopropane and methyl acetate. A triplet biradical intermediate formed by cleavage of the C(OMe)—N bond was postulated <90TL863>. Oxadiazolinone (42) underwent nucleophilic attack at the carbonyl group by methyllithium to give acetate (41) after treatment of the product with acetyl chloride <89CJC1753>. 

Amine promoters tend to give higher acetaldehyde rates relative to phosphines. Increasing the temperature to 200 increases the rate to 7.1 M/hr whereas decreasing the pressure to 2000 psig markedly lowers the rate. Lil is a critical component of the catalyst. Substituting Lil with Nal, KI, or CH I results in a substantial loss in catalytic activity. A key step in the postulated reaction mechanism, as outlined in Equations 16-18, is cleavage of methyl acetate by Lil to yield CH I and LiOAc (27). ... 

The final increase in the rate of hydrolysis of the esters of primary aliphatic alcohols, in 85-100% H2SO, is presumably due to acyl-oxygen cleavage, since methyl acetate reacts faster than the ethyl ester, which would not be the case for alkyl-oxygen cleavage. So also may be the rapid hydrolysis of aryl acetates at moderate acidity, since aryl-oxygen cleavage is not expected to be so rapid a reaction. 

An enantioselective synthesis of (+)-estradiol has been accomplished from 1,3-dihy-drobenzo[c]thiophene 2,2-dioxide (306) by successive thermal S02-extrusion and cycloaddition (80HCA1703). Treatment of the optically active iodide (307) with two mole equivalents of the masked quinodimethane (306) in the presence of two mole equivalents of sodium hydride gave (308) as a 1 1 mixture of diastereoisomers. Thermolysis of this alkenic sulfone in 1,2,4-trichlorobenzene furnished the trans-anti-trans steroid (309) in 80% yield. Treatment of (309) with methyllithium gave the methyl ketone, which was subjected to a Baeyer-Villiger oxidation and then silyl ether-acetate cleavage to afford (-l-)-estradiol (310 Scheme 66). 

The carbonylation of methyl acetate to acetic anhydride is likely to become an industrial process in the near future 424,427 RhCl3-3H20 is typically used as catalyst precursor and an iodide promoter is used. A mechanistic study indicated that methyl iodide formed from the ester and HI is carbonylated as in acetic acid synthesis (Scheme 26). The resulting acyl, perhaps via reductive elimination of acetyl iodide, converts the acetic acid formed in the ester cleavage to acetic anhydride.428 430 [RhI(CO)(PPh3)2] also catalyzes the reaction though apparently more slowly than complex (95).430,431 The mechanism of this reaction is given in Scheme 27. 

Methyl 8-oxooctanoate-4,5-D2, 35, and methyl 12-oxododecarbate-4,5,8,9-D4, 36, have been synthesized32 as shown in equations 13 and 14 by monoozonization and sodium acetate cleavage of 1,5-cyclooctadiene and 1,5,9-cyclododecatriene, respectively. The resultant unsaturated aldehydic acids 37 and 38 have been converted to the corresponding acetal esters, which have been deuteriated with Wilkinson s catalyst33 and hydrolysed to the deuterium-labelled aldehydic esters 35 and 36 in 47% and 49% overall yields and... 

Whereas the C2—C4 alcohols are not carboxylated under the usual Koch-Haaf conditions, carboxylation can be achieved in the HF-SbF5 superacid system under extremely mild conditions.400 Moreover, Olah and co-workers401 have shown that even methyl alcohol and dimethyl ether can be carboxylated with the superacidic HF-BF3 system to form methyl acetate and acetic acid. In the carboxylation of methyl alcohol the quantity of acetic acid increased at the expense of methyl acetate with increase in reaction time and temperature. The quantity of the byproduct dimethyl ether, in turn, decreased. Dimethyl ether gave the desired products in about 90% yield at 250°C (90% conversion, catalyst/substrate ratio =1 1, 6h). On the basis of experimental observations, first methyl alcohol is dehydrated to dimethyl ether. Protonated dimethyl ether then reacts with CO to yield methyl acetate [Eq. (5.154)]. The most probable pathway suggested to explain the formation of acetic acid involves the intermediate formation of acetic anhydride through acid-catalyzed ester cleavage without the intervention of CO followed by cleavage with HF [Eq. (5.155)]. 

Cleavage of acid-labile protective groups.1 The reaction of H202 (70%, FMC) and CI3CCOOH in CH2C12/(-butyl alcohol converts a dimethyl acetal (1) into a hydroperoxy methyl acetal (a), which can be isolated but which for convenience (and safety) is reduced to the aldehyde 2 in 80% overall yield. The same conditions can effect oxidative cleavage of tetrahydropyranyl and trityl ethers. 

Cleavage of -lactones.1 The blue solution of potassium-18-crown-6 in THF cleaves (3-propiolactone at -20° to furnish a dianion (1) which on protonation gives methyl acetate. A similar reaction of the (3-lactone 2 can be used to obtain isopropyl propionate (3). 

Hydrogenative carbonylation of methyl acetate to 1,1-diacetoxyethane followed by cleavage to vinyl acetate and acetic acid. Only syngas is involved as raw materials. 

Using 2,2-dimethylcyclobutanone [26a], as a specific example, initial excitation to produce an excited state species followed by a-cleavage would produce the acyl alkyl biradical [30]. Subsequent decomposition of [30] would then afford ester [27a] (via ketene), cyclopropane [28a], and acetal [29a], the observed photoproducts. The intermediacy of biradical [30] was supported by (a) the nearly exclusive formation of methyl acetate (as opposed to methyl isobutyrate), (b) the exclusive formation of the 5,5-dimethyl substituted acetal [29a] (as opposed to its 3,3-dimethyl substituted isomer), (c) its role as a common intermediate for all products, and (d) analogy to the photochemistry of cyclopentanones and cyclohexanones. Recently, Wasacz and Joullie have reported that photolysis of oxacyclohexanone [32] affords a 3% yield of acetal [29a] (18). It is conceivable that the formation of [29a]... 

Methyl acetals and ketals are rapidly reduced to methyl ethers by sodium cyanoborohydride in methanol with dry HCI at ice temperatures. A dioxolane is completely cleaved to a methyl ether, showing intervention by the solvent at some stage (equation 14), but when an inert solvent such as THF is used only single cleavage occurs this reagent shows interesting selectivity in the reduction of benzylidene acetals in the carbohydrate series (see Section 1.9.3.4). 

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