Heterocyclic compounds 1,3-dioxolane

Saturated five-membered heterocyclic compounds are non-planar, existing in half-chair or envelope conformations. The far-IR spectra of THE and 1,3-dioxolane (127) show both to have barriers of ca. 0.42 kJ moP ... 

The action of a Zn/Cu couple on 1,3-dibromo ketones and secondary amides yields 2-dialkylamino-1,3-dioxolanes (451 equation 208). Fluorosulfonic peracid anhydride adds to trifluoroacetonitrile to give an amide acetal (452 equation 209). In the addition of (Z)-2-butene-l,4-diol to trichloroacetoni-trile, catalyzed by sodium, the 1,3-dioxepin (453 equation 210) is produced. Bicyclic amide acetals (454 equation 211) are byproducts in the reaction of lactim ethers with diketene. TTie methyl esters of perfluorinated carboxylic acids react with diethanolamine to afford bicyclic amide acetals (455 equation 212). Heating of maleic anilides (456 equation 213) with acetic acid anhydride/sodium acetate gives heterocyclic compounds (457) containing an amide acetal structure. ... 

It should be pointed out that currently both trivial and systematic names are commonly used for naming the heterocyclic compounds. For example, an organic chemist will recognize without any difficulty the structures connected to names such as furane, pyrrole, pyrrolidine, pyrazole, imidazole, pyridine, or piperidine, despite the fact that all these names are trivial. On the other hand, the complex heterocycles require more sophisticated approaches in order to avoid ambiguity and correctly translate the chemical strucmre into the name. For these, compound names are often made using either trivial name (e.g., indazole for benzopyrazole, benzimidazole, indole, and isoindole) or the Hantzsch-Widman nomenclature, for example, 1,2,3- or 1,2,5-oxadiazoles, 1,3-dioxolane, 1,2- or 1,3-dithiolane, and 1,3- or 1,4-dioxane. It should be noted that the Hantzsch-Widman nomenclature treats the unsaturated heterocycle with maximum number of conjugated double bonds as parent compound. This adds another layer of complexity, giving rise to names such as... 

THERMODYNAMICS OF POLYMERIZATION OF HETEROCYCLIC COMPOUNDS. V. HEAT CAPACITY, ENTROPY, ENTHALPY, POLY-1,3-DIOXOLANE. 

In addition, silver-catalyzed asymmetric aza-Diels-Alder reactions provide a useful route to optically active nitrogen-heterocyclic compounds such as piperidines or pyrid-azines. Substituted dihydrobenzofurans can also be enantioselectively prepared through silver-promoted allylation of aldehydes. Other types of silver-mediated cyclizations can also be used in the synthesis of tetrahydrofnrans, tetrahydropyrans, 1,2-dioxetanes, 1,2-dioxolanes, medium-sized lactones, dihydroisoqninolines, and so on. Silver salts can also be used as cocatalysts with other transition metals. Unique activity was observed for these silver-based systems in several cases. Conseqnently, the use of silver can enrich several available heterocyclization methods, and fnrther developments in the application of chiral silver complexes will hopefnlly appear in the near future. 

Multicomponent reactions, which have been known for over 150 years, are those chemical transformations in which more than two reactants combine in a sequential manner to give highly selective products that retain majority of the atoms of the starting materials [36]. Because of the inherent molecular diversity, efficiency, and atom economy, they are highly sought after by chemists and have been widely used in the synthesis of some heterocyclic compounds. Hu and coworkers reported one unique example wherein the electron-rich aryl aldehydes selectively formed a carbonyl ylide with phenyldiazoacetate, which successively cyclized with electron-deficient aryl aldehydes to give the dioxolane (Scheme 2.22) [37]. 

Calculation of group increments for oxygen, sulfur and nitrogen compounds has allowed the estimation of conventional ring-strain energies (CRSE) for saturated heterocycles from enthalpies of formation. For 1,3-dioxolane, CRSE is about 20 kJ mol . In 2,4-dialkyl-l,3-dioxolanes the cis form is always thermodynamically the more stable by approximately 1 kJ mol" . 

Considering the formation of saturated five-membered heterocycles with two heteroatoms, it is worth to note the possibility to prepare 1,3-dioxolanes, dithiane, oxathianes 148 [93] and dioxolanones 149 [94] by condensation of the corresponding carbonyl compounds under microwave irradiation in acid medium (Scheme 52). The reaction, which is very useful for the protection of carbonyl compounds or for the preparation of useful synthetic intermediates, has also been carried out under batch conditions over Montmorillonite KIO clay in more than 150 g scale, using a 1 L quartz reactor [95]. 

Further applications were published, covering aralkylamino-quinazolines and other heterocycles (Eli Lilly [41]), new benzyl-substituted pyrimidines (Sumitomo [42]), aminoalkylspiro-l,3-dioxolanes (Shell [43]) and hydrazino-substituted pyrimidine compounds (BASF [44]). 

Synthesis of Heterocycles. Novel synthesis of 1,3-dioxolanes was suggested, which starts with the formation of an intermediate carbonyl ylide from dimethyl diazomalonate and a carbonyl compound (aldehyde or quinone) in the presence of catalytic amounts of Rh. Once formed, the ylide undergoes dipolar [3 + 2] cycloaddition with another equivalent of carbonyl compound to furnish a five-membered heterocycle (eqs 25 and 26). Employment of aldimines in this reaction allowed for preparation of 1,3-imidazolidines (eq 27) and 1,3-oxazolidines (eq 28). ... 

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