Ethylenic acetals

The PVA price has historically reflected the cost of ethylene, acetic acid, and energy. The price history for a medium molecular weight, fully hydrolyzed grade is 0.77/kgin 1970, 2.20/kgin 1980, 2.75/kgin 1988, and 2.65/kgin 1995. 

Most of the vinyl acetate produced in the United States is made by the vapor-phase ethylene process. In this process, a vapor-phase mixture of ethylene, acetic acid, and oxygen is passed at elevated temperature and pressures over a fixed-bed catalyst consisting of supported palladium (85). Less than 70% oxygen, acetic acid, and ethylene conversion is realized per pass. Therefore, these components have to be recovered and returned to the reaction zone. The vinyl acetate yield using this process is typically in the 91—95% range (86). Vinyl acetate can be manufactured also from acetylene, acetaldehyde, and the hquid-phase ethylene process (see Vinyl polymers). 

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). 

Phenylisoxazole has been obtained from the ethylene acetal of /3-benzoylacetaldehyde (300 R = Ph) and hydroxylamine (60ZOB954), and also from benzonitrile iV-oxide and acetylene (49G703), vinyl chloride (70S344), vinyl acetate (62BSF2215) or nitroethylene (76S612). 

The ethylene acetal A was also prepared by an alternative approach. 

Although this method is aot a geaeral procedure, bemg specific for ct-nitroketoues, k has several merits to avoid the use of toxic reageuts such as organodn compounds Functionalized ketones have been prepared by this denitration reaction, in which functionalized nitroalkanes are used as alkyl anion synthons For example, 3-nitropropanal ethylene acetal can be used as synthon of the 3-oxo-propyl anion and 1,4-dicarbonyl compounds are prepared, as shovm In Eq 7 88... 

Similarly, bromoacetaldehyde ethylene acetal with 3-aminobenzo [l,2,4]triazines 403 gave (82JHC61) linear tricyclic imidazobenzo[l,2,4] triazines 404 (Scheme 88). 

R,3S,45)-5-Benzyloxy-l-(l,3-dioxolan-2-yl)-3,4-bis(niethoxyinethoxy)-2-pentanol 6-0-Benzyl-2-deoxy-4,5-0-bis(methoxymcthyl)-L-xylo-hexose, ethylene acetal] syn,syn-l2. R = (l,3-dioxolan-2-yl)methyl Typical Procedure89 ... 

BrN3 13973-87-0) see Cefoxitin bromoacetaldehyde diethyl acetal (C6H 3Bt02 2032-35-1) see Domiodol bromoacetaldehyde ethylene acetal (C4H7Br02 4360-63-8) see Carbimazole IV-bromoacetamide... 

C21H2SO2 1096-38-4) see Algestone acetophenidc 4-demethoxydaunomycinone (C2oHi( 07 60660-75-5) see Idarubicin 4-demethoxy-4-(4-methoxybenzylamlno)daunomycinune I -ethylene acetal... 

Ci5H,iC1N202 22316-55-8) see Clobazam 4-7>-demethyIdaunomicinone I -ethylene acetal... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

This very mild Noyori acetalization has found wide application for the preparation of dialkyl or ethylene acetals of aldehydes and ketones, affording, e.g. with... 

Carbon dioxide can form as a result of combustion of ethylene, acetic acid, or vinyl acetate. The 1,2 C-ethylene experiments provided evidence on the role of Au and KOAc and its influence over the formation of carbon dioxide in the process. COj would be a characteristic of acetate decomposition, while COj would be characteristic of ethylene decomposition. 

Tetracyanoethylene (500 mg TCNE dissolved in 100 ml of acetonitrile or ethylene acetate) reacts with aromatic compounds, forming colored zones on a slightly yellow background. In some cases, heating to 100°C is necessary to complete the reaction. 

The arylation of the unsubstituted acrolein ethylene acetal with the bromopolyaromatics and bromoquinoline was studied in the presence of Pd(OAc)2 as catalyst (reaction conditions catalyst (2%), K2CO3, DMF, 110°C). The reaction was successfully performed with all evaluated poly(hetero)aromatics (Entry 5). 

Scheme 21.4 Intermediates formed during the aiylation of acrolein ethylene acetal.

The stereoselective total synthesis of (+)-epiquinamide 301 has been achieved starting from the amino acid L-allysine ethylene acetal, which was converted into piperidine 298 by standard protocols. Allylation of 297 via an. V-acyliminium ion gave 298, which underwent RCM to provide 299 and the quinolizidine 300, with the wrong stereochemistry at the C-l stereocenter. This was corrected by mesylation of the alcohol, followed by Sn2 reaction with sodium azide to give 301, which, upon saponification of the methyl ester and decarboxylation through the Barton procedure followed by reduction and N-acylation, gave the desired natural product (Scheme 66) <20050L4005>. 

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