2- -1,3-dioxolane hydrolysis

Dichloromethylene -1,3-dioxolane hydrolysis HCIO4 5-2 0-50 Gold and Waterman, 1968... 

Figure 6.38 Examination of the slower rates of hydrolysis of cyclic acetals compared with their acyclic counterparts (a) anti-ALPH nature of dioxolane hydrolysis p ° (b) two systems with identical structure-reactivity para-meters ° (c) recombination in a dioxolane hydrolysis (d) direct measurement of the relative rates of hydrolysis and recyclisation of the acyclic oxocarbenium ion intermediate in cyclic acetal hydrolysis.

The exocyclic 1,3-dioxolane ring is much more vulnerable to acid hydrolysis than the ring connected with the acetal group. Partial deprotection of the side-chain is easily achieved by treatment with sulfurie acid. 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

LiBF4, wet CH3CN, 96% yield.Unsubstituted 1,3-dioxolanes are hydrolyzed only slowly, but substituted dioxolanes are completely stable.This reagent proved excellent for hydrolysis of the dimethyl ketal in the presence of the acid-sensitive oxazolidine. ... 

The relative rate of acid-catalyzed hydrolysis of some dioxolanes [dioxolane aq. HCl (1 1)] are 2,2-dimethyldioxolane 2-methyldioxolane dioxolane, 50,000 5000 1. ... 

Dioxolanes can be cleaved by acid-catalyzed exchange dioxolanation, acid-catalyzed hydrolysis, or oxidation. Some representative examples are shown below. I... 

The acid-catalyzed hydrolysis of 2-alkoxy-2-phenyl-l,3-dioxolanes has been studied. The initial step is rate-determining under eertain eonditions and is deseribed by the rate law given below, whieh reveals general acid catalysis. 

A"" -3-Ketones are more reactive than cross-conjugated A ""-3-ketones. A"" -3,3-CycIoethylenedioxy compounds can be easily prepared by acid-catalyzed reaction with ethylene glycol or by exchange dioxolanation. 3,3-Cycloethylenedioxy-A -dienes can be prepared from 3,3-cycloethy-lenedioxy-A -enes by allylic bromination and dehydrobromination. Acid hydrolysis yields A"" -3-ketosteroids. ... 

Cleavage rates for 1,3-dioxanes are greater than for 1,3-dioxolanes/ but hydrolysis of a trans-fused dioxolane is faster than that of the dioxane. In substrates having more than one acetonide, the least hindered and more electron-rich acetonide can be hydrolyzed selectively." In a classic example, 1,2-5,6-diace-toneglucofuranose is hydrolyzed selectively at the 5,6-acetonide. 

Scheme 27).43b A regiospecific monohydroboration of enyne 107 with disiamylborane furnishes (A)-vinylborane 108, a substance that combines stereospecifically with vinyl iodide 109 under the indicated conditions to give conjugated triene 110 (52% overall yield). Trisporol B benzyl ether (111) is obtained after acid-induced hydrolysis of the dioxolane ketal functions.

This study is in excellent agreement with hydrolysis studies of 2-methyl-l, 3-dioxolane (17),... 

The pyruvic acid may also be linked to vicinal positions. When linked to 0-3 and 0-4 of a D-galactopyranosyl residue (40), the dioxolane ring becomes cw-fused. In the limited number of known examples, the absolute configuration at the acetalic carbon atom is (S), as in 40. There are some examples of tra -fused dioxolane rings, and these are more sensitive to hydrolysis with acid than the others. Thus, pyruvic acid is acetalically linked to 0-3 and 0-4 of an a-L-rhamnopyranosyl residue in the Klebsiella type 72 capsular polysaccharide, to 0-2 and 0-3 of an a-D-galactopyranosyl residue in the Streptococcus pneumoniae type 4 capsular polysaccharide, and to 0-2 and 0-3 of a S-D-glucopyranosyluronic acid residue in the Klebsiella K1 capsular polysaccharide. " In the extracellular polysaccharide from... 

The carbonyl group can be deprotected by acid-catalyzed hydrolysis by the general mechanism for acetal hydrolysis (see Part A, Section 7.1). A number of Lewis acids have also been used to remove acetal protective groups. Hydrolysis is promoted by LiBF4 in acetonitrile.249 Bismuth triflate promotes hydrolysis of dimethoxy, diethoxy, and dioxolane acetals.250 The dimethyl and diethyl acetals are cleaved by 0.1-1.0 mol % of catalyst in aqueous THF at room temperature, whereas dioxolanes require reflux. Bismuth nitrate also catalyzes acetal hydrolysis.251... 

The two reactions shown below are examples of the use of the Wacker reaction in multistep synthesis. In the first case, selectivity is achieved between two terminal alkene units on the basis of a difference in steric accessibility. Both reactions use a reduced amount of Cu(I) salt. In the second reaction this helps to minimize hydrolysis of the acid-sensitive dioxolane ring. 

Accordingly, the cyclopropenylidene anthrones 190/198 were converted by ferric chloride in hydroxylic solvents to the allene ketal 466, whose hydrolysis gives the allenic ketone 46 7288. The dioxolane 468 was obtained from the alkyl-substituted quinocyclopropene 190 in glycol and the ketone 467 in methanol. Apparently FeCl3 served not only as an oxidant, but also as a Lewis acid assisting solvent addition to C1 2 of the triafulvene. 

Cyclobutyl-cis-4-trans-5-dimethyl- 1,3-dioxolane, by reaction of erythro-3-methane-sulfonyloxy-2-butyl cyclo-butanecarboxylate with sodium borohydride, 51, 12 hydrolysis to cyclobutane-carboxaldehyde, 51, 13 3,5—CYCLOHEXADIENE—1, 2-DI CARBOXYLIC ACID, 50, 50 A1 a-Cyclohexaneacetaldehyde, 53, 104... 

Unsymmetrical vicinal diols can be prepared from a three-component reaction of aldehydes, CO, and aminotroponiminate-ligated titanium dialkyl complexes. Solutions of Me2TiL,2 (L = N -dimethylaminolroponiminalc) react rapidly with CO at room temperature. Double methyl migration to CO produces an 2-acclonc complex which inserts the aldehyde to afford a titana-dioxolane and releases the unsymmetrical diol upon hydrolysis [65]. 

Irreversible Transesterification. A new preparation of chiral glycerol acetonide (2,2-dimethyl-l,3-dioxolane-4-methanol) involving an enantioselective hydrolysis of 2-0-benzylycerol diacetate to the (R)-monoacetate catalyzed by a lipoprotein lipase (47) has recently been developed. In an effort to prepare the (S)-enantiomer, we have used the aforementioned irreversible transesterification reaction using isopropenyl acetate as an acylating reagent, which upon reaction gives acetone as a... 

Substituted 2-phenyl 1,3-dioxolanes 410 reacted with lithium and a catalytic amount of naphthalene (4%) in THF at —40 °C to yield intermediates 411 and products 412, after successive electrophilic substitution reaction at the same temperature and final hydrolysis (Scheme 115) . 

When 2,2-diphenyl-l,3-dioxolane (410, R = Ph) was lithiated with lithium and a catalytic amount of naphthalene (4%) in THF at —40°C (see Section VI.F.l) and then reacted with an aldehyde as electrophile, intermediates 437 were generated. The further lithiation of these compounds at the same temperature cleaved the second benzylic carbon-oxygen bond giving new organolithium intermediates 438, and a second electrophile could be introduced to give 439, after hydrolysis. In these products, two different electrophilic fragments have been incorporated, so the starting material behaves as the 1,1-diphenylmethane dianion synthon (Scheme 122) °. 

Reacting this with 1,2,4-triazole in the presence of sodium, followed by the hydrolysis of the protecting benzoyl group with sodium hydroxide gives 2-(2,4-dichlorophenyl)-2-(lH-1,2,4-triazol- l-ylmethyl)-4-hydroxymethyl-1,3-dioxolane... 

Finally, it should be mentioned that there exist two other routes for the synthesis of copolymers. First the partial chemical conversion of homopolymers (see Sect. 5.1), for example, the partial hydrolysis of poly(vinyl acetate). Secondly, by homopolymerization of correspondingly built monomers. An example for these macromolecular compounds, sometimes called pseudo-copolymers, is the alternating copolymer of formaldehyde and ethylene oxide synthesized by ringopening polymerization of 1,3-dioxolane. 

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