1.3- Dioxolane-4-methanol, 2,2-DIMETHYL

Ketones monobrominated at the less substituted carbon are not readily prepared by simple bromination of unsymmetrical ketones, since substitution occurs mainly at the more substituted carbon. While the action of hydrobromic acid on diazoketones has long been the only method of preparing bromomethyl ketones, it has recently been shown that bromination of unsymmetrical ketals, e.g.. dioxolanes or dimethyl ketals) occurs to a greater extent on the less substituted carbon atom, and this constitutes an efficient route to the corresponding a-bromo ketones.Direct bromination of 2-substituted cyclohexanones and various methyl ketones in methanol leads to the same result. 

Butyl myristate Butyloctanol Calcium sodium caseinate Caprylic/capric triglyceride Caprylic/capric triglyceride PEG-4 esters Ceteareth-11 Ceteareth-12 Ceteareth-16 Ceteareth-20 Ceteareth-33 Ceteth-20 Cholesterol Coco-betaine Corn oil PEG-8 esters Cl 2-13 pareth-23 Cl 2-15 pareth-2 phosphate Cl 2-15 pareth-8 phosphate Cl 2-15 pareth-10 phosphate 2,2-Dimethyl-1,3-dioxolane-4-methanol Dimethyl sulfoxide... 

Dimethyl cyclopentane 2,2-Dimethyl-1,3-dioxolane-4-methanol Dimethyl ether 2,6-Dimethyl heptanol-4 1,2-Dimethyl imidazole Dimethyl methylphosphonate 2,3-Dimethyl pentane 2,4-Dimethylpentane 3,3-Dimethyl pentane 2,2-Dimethylpropanol Dinonyl phenol Dioctyl adipate Dioctyl phosphite Dioctyl sebacate Diphenyl carbonate... 

CF,C02)2lPh, H2O, CH3CN, 85-99% yield. In the presence of ethylene glycol the dithiane can be converted to a dioxolane (91% yield) or in the presence of methanol to the dimethyl acetal. The reaction conditions are not compatible with primary amides. Thioesters are not affected. A phenylthio ester is stable to these conditions, but amides are not. The hypervalent iodine derivative l-(t-butylperoxy)-l,2-benziodoxol-3(l/f)-one similarly cleaves thioketals."... 

The low-temperature method has been applied to some primary and secondary alcohols (Fig. 1) For example, solketal, 2,2-dimethyl-1,3-dioxolane-4-methanol (3) had been known to show low enantioselectivity in the lipase-catalyzed resolution (lipase AK, Pseudomonas fluorescens, E = 16 at 23°C, 27 at 0oc) 2ia however, the E value was successfully raised up to 55 by lowering the temperature to —40°C (Table 1). Further lowering the temperature rather decreased the E value and the rate was markedly retarded. Interestingly, the loss of the enantioselectivity below —40°C is not caused by the irreversible structural damage of lipase because the lipase once cooled below —40°C could be reused by allowing it to warm higher than -40°C, showing that the lipase does not lose conformational flexibility at such low temperatures. 

Mejorado investigated the asymmetric addition of various organometallic nucleophiles using method A, but the reaction could not be catalyzed. The intermediates proved to be far too reactive. However, he established that the addition of a stoichiometric amount of a preformed chiral complex [an admixture of Taddol (r/om-a, -(dimethyl-1,3-dioxolane-4,5-diyl)bis(diphenyl methanol)) and EtMgBr] to 5 affords some enantiomeric excess in the resulting phenol product 6 (Fig. 4.12).13... 

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... 

The Hammett p-value for cleavage of the exocyclic bond of 2-methoxy-2-substituted-phenyl-l,3-dioxolans (—1.58 + 0.06) is a little larger than that for cleavage of the endocyclic C— bond of 2-hydroxy-2-substituted-phenyl-l,3-dioxolans (—1.24 + 0.04) (Table 9) (Chiang et al., 1983). A direct comparison between the p-values for C—OMe bond cleavage of trimethyl orthobenzoates and dimethyl hemiorthobenzoates is not possible at present since they have not been measured in the same solvent. However, that based on H+ for the breakdown of the hemiorthobenzoates (— 1.58) is less than that based on the equilibrium constants for their conversion into methyl benzoates and methanol which is —1.9 (derived from the equilibrium constants for formation of the hemiorthobenzoates, McClelland and Patel, 1981b). This implies that the development of positive charge in the transition state is less than in the final product, the ester. 

At ambient temperature a mixture consisting of the step 1 product (1.45 mol), 2,2-dimethyl-l,3-dioxolane-4-methanol (2.90mol), tetrabutylammonium hydrogensulfate (0.290 mol), and dimethylacetamide (2.11 kg) were treated with sodium hydroxide (3.63 mol). The mixture was then heated at 60°C for 3 hours and then recooled to ambient temperature and treated with hydroxylamine hydrochloride (2.32 mol). The mixture was stirred at 80°C for 2 hours and then cooled to 50°C. Thereafter, it was treated with butyl acetate (1.45 kg) and 1.45 liters of water and the organic layer... 

To a stirred solution of the step 2 product (4.12 mmol) dissolved in 20 ml THF was added a solution of the lithium salt of (2,2-dimethyl-[l,3]-dioxolan-4-yl)-methanol in 10 ml THF and the mixture refluxed for 18 hours. Upon cooling to ambient temperature, THF was partically removed and a concentrated solution/suspension of the crude product added dropwise to water. The aqueous mixture was then acidified to pH 5-6 and the precipitated polymer isolated. The polymer was redissolved in 50 ml 2 1 and then dried in vacuo at 50°C for several hours. The organic solution was extracted twice with 30 ml saturated sodium chloride solution and once with 30 ml of water. The material was dried using MgSO filtered, concentrated, and redissolved in a minimum amount of acetone and then precipitated into 100 ml hexane. Hexane was decanted, dried in vacuo, and the product isolated as a pale yellow viscous liquid in 60-90% yield. 

The photoreactions of saturated five-membered heterocycles are generally characterized by initial carbon-heteroatom bond homolysis. Tetrahydro-furans150 and 1,3-dioxolans151 behave in this way, and the major photoproducts of 2,2-dimethyl-1,3-dioxolan, for example, are acetone, propyl acetate, ethylene, acetaldehyde, methyl acetate, and oxiran. The vinyltetrahy-drofuran (180) is converted on irradiation in methanol to the ketal (181) and the ketone (182) by way of a Wagner-Meerwein shift in the carbocation... 

TTie most common methods generally used to prepare benzylidene acetals involve (a) reaction of a diol with benzaldehyde in the presence of p-toluenesul-fonic acid or a Lewis acid (usually zinc chloride)144 145 — a reaction that is accelerated by ultrasonication146 — or (b) reaction of the diol with benzaldehyde dimethyl acetal (a,a-dimethoxytoluene) in the presence of camphorsuifonic acid or p-toluenesulfonic acid as shown in Scheme 3.79.147 Both 1,3-dioxolanes or 1,3-dioxanes can be formed under these conditions. Yields may be improved by running the reactions under reduced pressure to remove the methanol as it is formed.88-148... 

As a Source of Other Chiral Building Blocks. The reagent is readily elaborated into several other key chirons, most notably the corresponding protected glycerol, (4/J)-2,2-dimethyl-l,3-dioxolane-4-methanol (1) obtained by sodium borohydride reduction of aqueous solutions of the reagent. ... 

Chlorination of (S)-2,2-dimethyl-l,3-dioxolane-4-methanol (324) with tri-phenylphosphine and carbon tetrachloride in the presence of a base gave 4-chloromethyl-2,2-dimethyl-l,3-dioxolane (325) (84MI4). The best stereoselectivity was achieved on the application of DBU. 

The linker is immobilized as 2,2-dimethyl-l,3-dioxolane-4-methanol (derivative of glycerol). 

Glycerol, isopropylidene- also l,3-dioxolane-4-methanol, 2,2-dimethyl-)... 

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