2.2- dimethyl-l,3-dioxolanes

Oxetan-3-one, 2-[2,2-dimethyl-4-(2,2-dimethyl-l,3-dioxolan-4-yl)-1,3-dioxolan-5-yl]-4-methyl-X-ray, 7, 366 <76JCS(P2)1678)... 

Aldehydes and ketones have been protected as acetals and dioxolanes using orthoformates, 1,2-ethanedithiol or 2,2-dimethyl-l,3-dioxolane by Hamelin and coworkers. This acid-catalyzed reaction proceeds in the presence of p-toluenesulfonic acid (p-TsOH) or KSF clay under solvent-free conditions (Scheme 6.2). The yields ob-... 

Unfortunately, the comparison is not reliable because the temperature was not measured in the domestic oven. Dioxolane formation by acid-catalyzed exchange between 2,2-dimethyl-l,3-dioxolane (DMD) and a ketone in a inert solvent, or simply in excess DMD, requires 4 to 7h under classical conditions [63], This reaction is readily achieved under microwave irradiation in high yields in 4 to 30 min (Scheme 8.43). 

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 double chiral-inductive asymmetric Michael addition of the camphor-based lithium ylide to 3-(45-2,2-dimethyl-l,3-dioxolan-4-yl)acrylate produces exclusively the... 

Z)-4-[(5)-2,2-Dimethyl-l,3-dioxolan -ylmethylene]-2-phenyl-5(47/)-oxazolone 632 can react as a dienophile in diastereoselective Diels-Alder reactions. Thus, 632 undergoes a thermally induced Diels-Alder reaction with cyclic dienes, for example, cyclopentadiene and cyclohexadiene, to afford a mixture of the four... 

The X-ray crystal structure of fZ)-4-[(5)-2,2-dimethyl-l,3-dioxolan -ylmethyl-ene]-2-phenyl-5(4//)-oxazolone has been determined. " The analysis shows an almost planar disposition for the entire molecule with the exception of the dioxolane ring that adopts an envelope conformation. As such, the dioxolane ring is mainly situated on the si,si diastereotopic face of the olefinic bond, a situation that accounts for the observed diastereoselectivity in Diels-Alder reactions. 

In 1990, Wong disclosed in a patent literature that a propylene/CO alternating co-polymer arising from a Pd-based catalyst and (—), 5-bis(dibutylphosphinomethyl)-2,2-dimethyl-l,3-dioxolane as a chiral ligand displayed a specific rotation of 10.4 in (CF3)2CHOH. This represents the first example of asymmetric alternating co-poly-... 

It has recently been demonstrated that a stereoselective synthesis of dipeptides by hydrogenation of the corresponding monodehydropeptides (N-protected free acids or methyl esters) is possible. In this reaction, chiral catalysts, for example BPPM (13), in the form of a Wilkinson complex have been used. These are superior to the corresponding DIOP complexes (DIOP = P,P -[2,2-dimethyl-l,3-dioxolane-4,5-bis(methylene)]bis(diphenylphosphane). A d.s. value of 90—99% was generally obtained 49 ... 

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... 

Preparation of trifluoroethoxy/(2,2-dimethyl-[l,3]-dioxolan-4-yl)-methoxy polyphosphazene... 

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. 

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