Diethylacetals

Probably first obtained by Hantzsch and Arapides (105) by condensation of a,/3-dichlorether with barium thiocyanate, and identified by its pyridine-like odor, thiazole was first prepared in 1889 by G. Popp (104) with a yield of 10% by the reduction in boiling ethanol of thiazol-2-yldiazonium sulfate resulting from the diazotization of 2-aminothiazole. prepared the year before by Traumann (103). The unique cyclization reaction affording directly the thiazole molecule was described in 1914 by Gabriel and Bachstez (106). They applied the method of cyclization, developed by Gabriel (107, 108), to the diethylacetal of 2-formylamino-ethanal and obtained thiazole with a yield of 62% - Thiazole was also formed in the course of a study on the ease of decarboxylation of the three possible monocarboxylic acids derived from it (109). On the other... 

Halogenopyrimidines react with active methylene groups, such as those in diethyl malonate, ethyl cyanoacetate, ketene diethylacetal, etc. For example, 4-chloro-6-methyl-5-nitropyrimidin-2-amine (454) and dimethyl sodiomalonate give dimethyl 2-amino-6-methyl-5-nitropyrimidin-4-ylmalonate (455) (63ZOB3132) 2-chloro-4,6-... 

Acetal (acetaldehyde diethylacetal) [ 105-57-7] M 118.2, b 103.7-104 , d 0.831, n 1.38054, 1.3682. Dried over Na to remove alcohols and water, and to polymerise aldehydes, then fractionally distd. Or, treat with alkaline H2O2 soln at 40-45° to remove aldehydes, then the soln is saturated with NaCl, separated, dried with K2CO3 and distd from Na [Vogel J Chem Soc 616 1948]. 

Cinnamaldehyde dimethylacetal is prepared by the method used to prepare the corresponding diethylacetal. A mixture of 66.0 g. (0.5 mole) of Aldrich Chemical Company, Inc.), 100 g. (1.06 mole) of trimethyl orthoformate (Eastman Organic Chemicals), 450 ml. of anhydrous methanol (J. T. Baker Chemical Company), and 0.5 g. ofp-toluenesulfonic acid monohydrate (Fisher Scientific Company) is stirred at room temperature for 24 hours. At the end of this time the alcohol is removed with a rotary evaporator and the residue is distilled to give 81-83 g. (91-93%) of cinnamaldehyde dimethylacetal, b.p. 93—96° (0.2 mm.). 

Diastereotopism indicates prochirality, as exemplified by glycerol (25, Fig. 2.23). Other examples of this include diethylacetals, in which the OC//2 protons are diastereotopic on account of the prochiral acetal-C atoms, thus forming AB systems of quartets because of coupling with the methyl protons. 

Trichloro-s-triazine also reacts readily with carbon or phosphorus nucleophiles. Diethylmalonate anion forms a mono-derivative under mild conditions and the tri-substitution product (327) under vigorous conditions with excess nucleophile. Nucleophilic attack by the 7r-electrons of ketene diethylacetal to give 254 and of dimethylaniline to give 253 has been mentioned earlier. Two... 

Upon heating with a mixture of concentrated hydrochloric acid and ethanol under reflux, the hexaminium salt 4 is cleaved into the primary amine and formaldehyde. The latter can further react with ethanol under the acidic conditions to give formaldehyde diethylacetal ... 

A dicarbocyanine dye, dithiazinine (79), is used as a broad-spectrum anthelmentic agent, although, interestingly, it seems to have been prepared initially for use in photographic emulsions. It is made by heating 2-methylbenzothiazole ethiodide (77) with the malondialdehyde equivalent, B(ethylmercapto)-acrolein diethylacetal (78) in the presence of pyridine. There apparently ensues a sequence of addition-elimination reactions quenching the reaction mixture with potassium iodide solution results in separation of green crystals of dithiazanine iodide (79). ... 

An imidazole derivative which is also a hypotensive agent by virtue of adrenergic a-2-receptor blockade is imiloxan (75). Its synthe.sis begins by conversion of 2-cyanomethyl-1,4-benzodioxane (72) to its iminosMhylether with anhydrous HC in clhanol (73). Reaction of the latter with aminoacetaldehyde diethylacetal and subsequent acid treatment produces the imidazole ring (74). Alkylation of 74 with ethyl iodide mediated by sodium hydride completes the synthesis [251. 

Chloropropionaldehyde diethylacetal 8enzilic acid Piperidine Hydrogen chloride... 

Ethylthioacrolein diethylacetal Dithiazanine iodide Ethyl thioglycolate Piprozolin... 

Scheme 21.1 Heck arylation of acrolein and acrolein diethylacetal. was the most important parameter among all those evaluated (i.e. KCl, solvent...) that affect the selectivity (Scheme 21.1, Route 3). However, moderate activity and selectivity were achieved when using the 9-bromoanthracene whatever the olefin (8). This was attributed to the large steric hindrance of this substrate.

Ketene diethylacetal, 23, 43 Ketene, diethyl ketal, 23, 43 Ketene dimer, 21, 4, 64 Ketene lamp, 21, 65 Keto acid, 20, 2... 

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. 

The condensation of cyanoguanidine and aminoacetal (or its methyl-homologue) yields the expected diethylacetal of biguanidoacetaldehyde this is cyclisable to 2-guanidinoimidazole (or its 1-methyl-homologue) (VIII) by means of mineral acids (576). 

Hydrolysis of the diethylacetal function employing p-toluenesulphonic acid in acetone, pyridinium p-toluene-sulphonate in EtOH, and a suspension of Si02 in hexane. In all cases the corresponding aldehyde is obtained in high yield as a Z E isomeric mixture. Transmetallation of acetal with Me2Cu(CN)Li2 followed by treatment with c-hexenones giving the 1,4-addition product. Alternatively, transmetallation with n-BuLi and reaction with benzaldehyde giving the expected alcohol. 

The replacement of ring C by a cyclic anhydride ring could be looked upon either as elimination of ring C or replacement of the ring by a heterocyclic anhydride ring. In any case, Fields et al. showed that quinolizinium 2,3-dicarboxylic acid anhydride (37) underwent cycloaddition reactions with either cyclopentadiene or styrene to alFord the expected products (e.g., 38). The 2,3-dimethylquinolizinium ion did not undergo cycloaddition even with the more reactive ketene diethylacetal. 

One method for the synthesis of thienobenzazocines is bicyclization of Al-thienylmethyl-N-arylmethylaminoethanal diethylacetal 169 with substituted aryl... 

Methimazole Methimazole, l-methyl-2-imidazolthiol (25.2.5), is synthesized by reacting aminoacetic aldehyde diethylacetal with methylisothiocyanate and snbseqnent hydrolysis of the acetal group of the resulting disubstituted urea derivative 25.2.4 by a solution of sulfuric acid, during which a simultaneous cyclization reaction takes place, forming the imidazole ring of the desired methimazole [15,16]. 

The chemistry of 1,4-(oxa/thia)-2-azoles, was founded in the late 1930s, when Musante first correctly suggested the 5-imino-2-phenyl 1,4,2-oxathiazole structure (1) for the product obtained from the reaction of ammonium thiocyanate and benzhydroximoyl chloride <38G33l>. Later, Beck described the preparation of dioxazolones (2) and some of their properties <51CB688>, while the first nonconjugated dioxazole derivative (3) was prepared by Exner from hydroxamic acid and benzophenone diethylacetal <56CLY779>. 

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