1,3-Dioxolanes, 4-substituted

Many copolymerization studies have been made. A detailed discussion and critique of the results has been pubHshed (1) and the breadth of the comonomers studied has been summarized (6). Among the comonomers used are oxiranes, oxetanes, 1,3-dioxolane, substituted tetrahydrofurans. 

Wolak MA, Melinger JS, Lane PA, PaUlis LC, Landis CA, Delcamp J, Anthony JE, Kafafl ZH (2006) Photophysical properties of dioxolane-substituted pentacene derivatives dispersed in tris(quinolin-8-olato)aluminum(III). J Phys Chem B 110 7928-7937... 

Wolak MA, Delcamp J, Landis CA, Lane PA, Anthony J, Kafafi Z (2006) High-performance organic light-emitting diodes based on dioxolane-substituted pentacene derivatives. Adv Funct Mater 16 1943-1949... 

In the previous paragraph we discussed polymerization of 1,3-dioxolans substituted at and C, Information on the polymerization of dioxolans substituted at C2 is very limited we shall confine ourselves to the polymerization of 2-vinyl-dioxolans and 2-vinyl--dioxans. 

Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

Miscellaneous OC-Substituted Peroxides. 3-Aryl-3-(/ i alkylperoxy)-phthaHdes (12) are prepared from the corresponding 3-chlorophthaHdes and alkyl hydroperoxide (156). 2-Methyl-2-(/ f2 -alkylperoxy)-l,3-benzodioxan-4-ones (13) are obtained from 0-acetylsaHcyloyl chloride and alkyl hydroperoxides (157). Trisubstituted 2-(/ f2 -alkylperoxy)-l,3-dioxolan-4-ones (14) are synthesized from stericaHy favored a-acyloxy acid chlorides and alkyl hydroperoxides (158). 

Ketoconazole. For treatment of systemic mycoses with amphotericin B or miconazole, the patient must be admitted to a hospital. This is not always possible, particularly in areas where systemic mycoses occur frequently, nor is it always desirable, because of the expense. For these reasons, it was desirable to find an antimycotic that combined safety and broad-spectmm activity with oral adraiinistration. Ketoconazole (10), which is orally active, met most of these requirements. This inhibitor of the ergosterol biosynthesis is an A/-substituted imidazole, that differs from its precursors by the presence of a dioxolane ring (6,7). Ketoconazole is rapidly absorbed in the digestive system after oral adrninistration. Sufficient gastric acid is required to dissolve the compound and for absorption. Therefore, medication that affects gastric acidity (for example, cimetidine and antacids) should not be combined with ketoconazole. 

To synthesize isomeric 3-substituted isoxazoles (301) the reaction of ethylene acetals of )3-ketoaldehydes (300) (readily available from -chlorovinyl ketones (57IZV949)) with hydroxylamine was employed. Owing to the comparative stability of the dioxolane group, this reaction gave exclusively 3-substituted isoxazoles (301) (60ZOB954). The use of noncy-clic, alkyl S-ketoacetals in this reaction resulted in a mixture of 3- and 5-substituted isoxazoles (55AG395). 

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 5-substituted 1,3-dioxolan-4-one 23 is readily deprotonated at the 5 position and can be alkylated with a variety of alkyl halides. The resulting products 24 decompose upon flash vacuum pyrolysis (FVP) at 600°C with loss of acetone... 

Substituted A,A-dialkyl(cycloalkyl)furfurylamines and their quaternary salts, 2-substituted 1,3-dioxolanes, oxathiolanes, and -dithiolanes, as antagnoists and muscarinic receptors 98F1. 

Substituted 4-aryl-l,3-dioxolanes are ring opened by TiCU and at low temperatures subsequently recyclise ortho to the activating group on the aryl ring to give 4-hydroxyisochromans. A further stereoselective isomerisation to henzofurans occurs at higher temperatures <96JCS(P1)2241>. 

Reaction of ketones such as 1-menthone 398 with silylated glycolic acid 417 in the presence of catalytic amounts of TMSOTf 20 provides an lil-mixture of the l,3-dioxolan-4-ones 418 and 419 [35, 36]. Likewise, other aldehydes and ketones [37, 38] and pivaldehyde [39] react with substituted silylated glycohc adds 420 a, b and yS-hydroxy acids 420c to give, e.g., 421 a, b and 421c as mixtures [37-40]. Reaction of pivaldehyde with the persilylated hydroxy acid 420 d and TMSOTf 20 to... 

Dioxane reacts with trimethylsilyl iodide 17 to give 96% 1,2-bis-iodoethane, 53% l,2-bis(trimethylsilyloxy)ethane, and 32% HMDSO 7 ]5, 29]. 1,3-Dioxolane 840 furnishes, via 841, iodomethyl-2-iodoethyl ether 842 and HMDSO 7 ]5, 30] (Scheme 6.13). 2-Substituted 1,3-dioxolanes 843 are converted by trimethylsilyl iodide 17, via a series of postulated intermediates, into 1,2-diiodoethane, the ester 844, the alkyl iodide 845, and HMDSO 7 [5] (cf also Chapter 5, Scheme 5.67). 

Scheme 21.5 Synthesis of diethyl 2-substituted-[l,3]-dioxolane-4,5-diaeetate.

When 4-substituted 2,2-dimethyl- 1,3-dioxolanes react with Grignard reagents, the bond that is broken is the one at the oxygen attached to the less-substituted a-carbon. What factor(s) are likely the cause for this regioselectivity ... 

Another characteristic of PCP which has been studied with great interest over the last 5 years, is the ability of PCP to produce a discriminative stimulus in monkeys, rats, and pigeons. As discussed elsewhere in this volume, by Browne, the discriminative stimulus properties of PCP are shared not only by other members of the arylcycloalkylamine class, but by psychotomimetic benzo-morphans and substituted dioxolanes. The structure-activity relationships (SAR) within and between these classes are virtually identical to those found when studying the displacement of 3H-PCP from its binding site in rat brain membranes. This correlation... 

Dioxacycloalkanes are cyclic acetals that are used frequently as protective groups. Substituted derivatives have been synthesized to achieve easy removal. Simplest of all, the 4-phenyl-1,3-dioxolane has not been used commonly because cleavage needs electrolytic conditions. A mild hydrogenolysis method was developed in 1997 to make this protective group more popular (Scheme... 

Finally, Scharf and Wolters report a method said to be superior to both the Paal-Knorr synthesis (starting materials more easily accessible) and the Feist-Benary synthesis (freer choice for 3-substituent). Thermal rearrangement-elimination by alkylated dioxolanes at 230 C gives alkyl substituted furans. Yields can be nearly quantitive since the only serious by-products also give the furans under proton-catalyzed thermolysis (Scheme 25).124 Photochemical methods are outlined in Section VII. 

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. 

The 1,2,4-oxadiazole dioxolanes 144 react with hydroxylamine and hydrazines to form the 5-pyrazole- and isoxazole-substituted 1,2,4-oxadiazoles 146 via the dioxolane ring-opened intermediates 145 (Scheme 17). Reaction of compounds 144 with amidine or guanidine salts allows access to pyrimidine substituted analogues 147, via intermediate 145 (X = C(NH)R1), albeit in lower yield <1996JHC1943, 1998JHC161>. 

Furthermore, it has been demonstrated in acetals of phenyl alkyl ketones that the presence of the aromatic moiety at the anomeric carbon induces a further stabilization resulting in very strong anomeric stabilization.29 This phenomenon is reminiscent of the stronger methyl substitution effects discussed above for 1,3-dioxolane and 1,3-dioxane (see also Table 1) than for alkyl ethers and alkanes. 

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