Halo acetates preparation

Ketene di(2-melhoxyethyl) acetal has been obtained by the present method with the use of diethylene glycol dimethyl ether as solvent.3 Other methods for the preparation of ketene acetals include the dehydrohalogenation of a halo acetal with potassium t-butoxide 4 and the reaction of an a-bromo orthoester with metallic sodium.5... 

The cyclizations of halo acetals, introduced by Stork66 and Ueno,67 are among the most popular of all radical methods because the precursors are easy to prepare, the cyclizations are very rapid, and the products can be converted to a variety of different heterocycles. The conversion of (26) to (28 Scheme 17) illustrates the basic procedure.68 Standard bromoacetalization of an alcohol provides the precursor (27). After tin hydride cyclization and acidic oxidation, lactone (28) is formed in excellent yield with 97%... 

Halo acetals, amination, 669 dehydrohalogenation, 37, 79 preparation, 101, 263, 269 Halo acids, amination, 669 decarboxylation, 79 dehydrohalogenation, 38, 79 esterification, 481 in the Williamson reaction, 228 lactonization, 535 preparation, by cleavage of ethers, 93... 

Halo acetals have been prepared by the action of alcohol on halo ketones and halo aldehydes.An indirect application of this reaction consists in the halogenation of enol acetates with subsequent reaction of the brominated products with alcohols to give the halo acetals. ... 

For syntheses requiring the syn adducts, it is more practical to use the boron enolate without additional Lewis acids [75], since the auxiliary is available as either enantiomer and is recoverable. On the other hand, the anti adducts are (so far) only available by the diethylaluminim chloride/boron enolate protocol [66]. Similar principles may be used to prepare syn and anti halohydrins by aldol addition of a-halo acetate enolates of Evans imides [90,91]. 

Free a>bromo aldehydes are obtained from their acetals by brief heating (1 min) in dioxane-water-concentrated HC1 (10 5 1), immediate cooling, dilution with water, and extraction with ether.655 For the preparation of oc-halo acetals by way of /3-dihalo ethers see also page 111. 

As an extension of this new procedure for carbon-carbon bond formation, the reaction between silyl enol ethers and acetals 50, a typical protecting group of aldehydes, is performed to afford j5-alkoxy carbonyl compound 51 in the presence of titanium(IV) chloride (Eq. (24)) [27]. A variety of substituted furans are readily prepared by application of the TiCU-promoted reaction of a-halo acetals 52 with silyl enol ethers (Eq. (25)) [27]. 

Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%)." In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

There are very few precedents for the reaction of cyclic a-halo ethers with carbanions. Zelinski and coworkers114 and Schudel and Rice115 reported the preparation of diethyl DL-tetrahydropyran-2-ylmalonate (137) by treatment of 2-bromo- or 2-chloro-tetrahydropyran (136) with diethyl sodiomalonate. The product was subsequently converted into the malonic and acetic acid derivatives, 138 and 139, respectively. The same sequence has also been reported by other workers.116... 

The ammine complexes of Co3+ are prepared by adding excess ammonia to a solution of cobalt salt followed by air oxidation and boding. The brown solution turns pink on boiling. The cyanide complexes are made by adding excess potassium cyanide to a solution of cobalt salt. Acidification of the solution with a small amount of acetic or hydrochloric acid followed by boiling yields K3Co(CN)6. The aquo-halo mixed complexes are formed by stepwise substitution of H2O molecule with halide ion in the coordination sphere. In general, a mixed complex may be prepared by substitution with a specific anion. 

Halogenation of dibenzofuran produces the 2-halo compounds. Bromina-tion can be achieved in good yield with bromine in acetic acid " or with N-bromosuccinimide in boiling carbon tetrachloride. The 2,8-dibromo compound has been made, using dioxane dibromide. Chlorination of dibenzofuran in acetic acid in the presence of iron powder can be controlled to yield the 2-chloro or the 2,8-dichloro compounds. 2-Chlorodi-benzofuran is best prepared by reaction of dibenzofuran with phosphorus pentachloride. 2-Iododibenzofuran (45%) results from treatment of dibenzofuran with iodine in boiling chloroform in the presence of nitric acid. 2,8-Diododibenzofuran is best prepared by reaction of dibenzofuran with iodine and iodic acid in aqueous acetic acid. ... 

An efficient chemical process for closing a diphenylamine is that using palladium(II) acetate (2 mol for substrates carrying electron-withdrawing groups) in acetic acid-methanesulfonic acid. Carbazole formation has been achieved with alkyl-, halo-, nitro-, and carboxyl-substituted diphenylamines. 1-Chlorocarbazole and carbazol-l-yl carboxylic acid as examples were efficiently prepared. - This is probably the best method now available for cyclizing diphenylamines. 

Preparation of enamines, 409 Preparation of enol acetates, 411 Preparation of enol ethers, 409 Preparation of a-halo ketones, 267 Preparation of 3/3-hydroxyandrosta-5,15-dien-17-one, 302... 

A large number of 5-deazaflavins (32 R1, R2 = H, alkyl, aryl R3, R4 = H, Cl, NO2, OH 48 examples in all), have been prepared in good yields via condensation of 6-substituted aminouracils with o-halo-benzaldehydes in DMF under reflux. The mechanism shown in Scheme 14 was proposed for this reaction.138 Several bis(5-deazaflavin-10-yl)alkanes (33 n = 6, 8, 10, 12) have also been prepared via the same route using bis(uracil-6-ylamino)alkanes.138 By an analogous reaction the substituted quinolines (34a) and (34b) were obtained in 87% and 50% yield, respectively, from enaminones (35a X = Y = NMe Z = O) and (35b X = Y = CH2 Z = Me2) and pentafluorobenzaldehyde in glacial acetic acid at reflux.139... 

Cyclization occurs directly through catalysis by the acid liberated when a pyridine-2(lH)-thione is heated with an a-halo acid ester. The most convenient method for preparing the thiazole, however, seems to be the cyclization of (2-pyridinethio)acetic acids in acetic anhydride in the presence of pyridine. Without base catalysis the reaction is slow, which suggests a mixed anhydride intermediate. Mixed anhydride formation with ethyl chlorofor-mate in pyridine, or carboxyl activation by DCC in pyridine, gives the mesoionic product. The cyclization reaction and the chemical stability of the thiazole are adversely affected by a pyridine 6-substituent. The initially formed acylpyridinium salt (407) undergoes rapid tautomerization to the aromatic thiazole form equilibrium between the forms (407) and (408) is verified by rapid deuteration at C-2 (R1 = H) in AcOH-d (81H(15)1349). 

The dimeric tetraacetato bridged Rh2(OCOCH3)4 has been obtained by the interaction of ammonium chlororhodate(III) or rhodium (III) hydroxide with acetic acid.1-3 Other (car-boxylato)rhodium(II) compounds were prepared directly in a similar way or from the acetate by exchange.2,3 Halo car-boxylates (RCOO, R = CC13, CF3, CH2C1, etc.) were prepared also by interaction of rhodium trichloride with the appropriate sodium salt in ethanol.4 The carboxylatcs are normally first isolated as a solvent adduct, e.g., [Rh(OCOR)2-C2H5OH]2 but are easily converted to the unsolvated complex. The acetate is readily prepared in a modification of this last procedure. A similar method is satisfactory for the preparation of other lower carboxylates as well as halo carboxylates. 

The dihydrotriazoles prepared by cycloaddition of aryl, heteroaryl, and alkyl azides to 3,4-di-azatricyclo[4.2.1.02,5]nona-3,7-diene and 3,4-diazatricyclo[4.2.1.02,5]non-7-ene derivatives were smoothly converted to exo-aziridines by treatment with catalytic amounts of adds (acetic, trifluoroacctic, sulfuric) in aprotic solvents (diethyl ether, dichloromethane, dioxane) at 25-80°C for 4-48 hours, e.g., the sequence 9 -> 10 -> 11 or 12 -> 13 -> 14. The aziridines were further converted to (6-halo and (6-hydroxy aminesl03b. 

Dialdehydes result when cyclic olefins are ozonized. Improved directions for the ozonolysis of unsaturated esters in glacial acetic acid to yield aldehyde esters have been given. The same procedure is applied to the preparation of aliphatic aldehydes containing halo, hydroxyl, and ether groups. ... 

The reduction of diazonium salts by sodium sulfite forms monosub-stituted arylhydrazines. An improved procedure for the synthesis of phenylhydrazine in 84% yield is typical. Arylhydrazine salts substituted in the nucleus with halo," ether, carboxyl, or nitro groups have been prepared. The free bases are liberated from the salts by the action of aqueous sodium hydroxide or sodium acetate. 

Dihalides, preparation, 93, 97 Dihalo acetals, elimination of halo and... 

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