Dimethoxy ketal

Reductive Carbonylation of Dimethoxy Ketals and Dimethyl Carbonate. Acetaldehyde is obtained via the reductive carbonylation of dimethyl ketals. Equation 12, and dimethyl carbonate. Equation 13 (15). 

The synthesis of the twistane-ketal 279 using endo-6-hydroxy-9-oxabicyclo[3.3.1]-nonan-2-one (274) or its acetate 227, resp., was nevertheless successful by applying the following route according to a procedure by Inhoffen etal. the keto-acetate 221 was treated with trimethyl orthoformate. From the reaction mixture which contained the dimethoxy-ketals 222 and 223 as well as the enolethers 224 and 225, the acetates 222 (63%) and 224 (5%) were isolated by chromatography. On base-hydrolysis they gave the alcohols 223 and 225. Pyrolysis of the ketal 222 and simultaneous distillation yielded 67% of the enolether 224. Finally by treating the dime-... 

Further examples of synthetic application of the para-alkoxylation reaction include the preparation of dimethoxy ketal 231, which is an essential precursor in the enantioselective synthesis of the potent antifungal agent (-)-jesterone [297], the synthesis of various dimethoxy ketals of para- and ort/to-benzoquinones [298] and the methoxylation of various phenolic substrates, such as 232, using (diacetoxyiodo)benzene in methanol (Scheme 3.95) [299-301]. 

Two additional mixed ketals, aplysinketal A (5) and aplysinketal B (6), along with 7 and 8, were obtained from the Mexican sponge Aplysina (Verongia) thiona (7). Unlike 2 and 3, the structure of aplysinketal A (5) was shown to be only one of the two diastereoisomers by X-ray and NMR data. Furthermore, the mixed ketals 5 and 6 would not be expected to be formed without simultaneous formation of the dimethoxy ketal 2, which was never detected. According to these results, aplysinketal A (5) and aplysinketal B (6) are very likely to be natural products. The diethyl ketal 9 was obtained from a Turkish sponge V. aerophoba (8). 

In addition, the cyclopentylidene ketal has been prepared from dimethoxy-cyclopentane, TsOH, CH3CN, or cyclopentanone (PTSA, CUSO4 >70% yield) and can be cleaved with 2 1 ACOH/H2O, rt, 2 h. Certain epoxides can be converted directly to cyclopentylidene derivatives as illustrated in the following reaction ... 

It is interesting to note that among initiators studied, a benzyl ketal type initiator (2,2-dimethoxy-2-phenyl acetophenone) is more active than other initiators of acetophenone type. 2,2-Dimethoxy-2-phenyl acetophenone is more active than BME, probably due to the presence of the extra methoxy group on the -carbon, which gives a more active phenyldimethoxy methyl radical (and it further cleaves to give an even more active methyl radical) than the phenylmethoxy methyl radical from BME (4). It is known that the phenylmethoxy methyl radical dimerizes easily and thus loses some of its role as a radical in a... 

Adduct 5 has been isolated as the sodium salt in two different ways, i.e., either by solvent evaporation of the reaction mixture as obtained from equivalent amounts of the starting reagents in methanol solution,37,38 or by chilling a solution of 4-chIoro-3,5-dinitropyridine and sodium meth-oxide.15,49 The IR spectrum of the solid thus obtained shows a series of strong bands between 1040 and 1225 cm"1, which are typical of ketals, in agreement with the presence of a geminal dimethoxy grouping. The NMR spectrum... 

Protection of aldehydes and ketones.1 Bis-o-nitrobenzyl acetals or ketals are removable in 85-95% yield on irradiation at 350 nm in benzene. The acetals or ketals are easily prepared from 1 by an exchange reaction using 2,2-dimethoxy-propane (1, 268-269) catalyzed by an arenesulfonic acid. In the case of hindered ketones (17-keto steroids), the glycol o-N02C6H4CH(OH)CH2OH (2) can be used. 

This section deals only with solvents whose reduction products are insoluble in the presence of lithium ions. The list includes open chain ethers such as diethyl ether, dimethoxy ethane, and other polyethers of the glyme family cyclic ethers such as THF, 2Me-THF, and 1,4-dioxane cyclic ketals such as 1,3-dioxolane and 1,3-dioxane, esters such as y-butyrolactone and methyl formate and alkyl carbonates such as PC, EC, DMC, and ethylmethyl carbonate. This list excludes the esters, ethyl and methyl acetates, and diethyl carbonate, whose reduction products are soluble in them (in spite of the presence of Li ions). Solutions of solvents such as acetonitrile and dimethyl formamide are also not included in this section for the same reasons. Figure 6 presents typical steady state voltammo-grams obtained with gold, platinum, and silver electrodes in Li salt solutions in which solvent reduction products are formed and precipitate at potentials above that of lithium metal deposition. These voltammograms are typical of the above-mentioned solvent groups and are characterized by the following features ... 

Oligomeric benzil ketals (DTGPA), prepared by reaction of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) with triethyleneglycol, in the presence of p-toluen-sulphonic acid, are reported [88] to be efficient in the UV curing of styrene/ unsaturated polyester formulations giving rise to coatings with very low odour. 

A one-step synthesis of 4-methylpyrimidine involves heating a mixture of formamide, solid ammonium chloride, and a small volume of water to 180-190°, and adding 4,4-dimethoxy-2-butanone in the course of 6 hrs. The ammonium chloride serves as an acidic salt to hydrolyze the ketal bonds. 

The synthesis of unnatural (+)-mesembrine (387) through the asymmetric synthesis of methyl (i )-l-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390) by cycloaddition of enantiomerically pure vinyl sulfoxide with dichloroketene has been performed 189) (Scheme 43). Vinyl sulfoxide 388 [prepared by conjugate addition of enantiopure acetylenic sulfoxide with (3,4-dimethoxy)phenylcopper] reacted with trichloroacetyl chloride in the presence of freshly prepared zinc-copper couple in THF at 0°C to produce a mixture of mono- and dichloro lactones 389. Reduction of 389 with zinc in acetic acid followed by cyclization and methylation afforded methyl IR-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390), treatment of which with methylamine brought about amidation and concomitant intramolecular Michael addition to provide 2-oxo-mesembrine (391). Successively, 391 was transformed to (+)-mesembrine (387) in 79% yield (three steps ketalization of an oxo group, reduction of lactam, and deketali-zation)(/S9). 

Diels-Alder dienes Benzene, see Dicyanoacetylene. Cyclooctatetraene, see 4-Phenyl-l,2,4-triazoline-3,5-dione. Cyclopentadiene ketals. cis-7,8-Dichlorobicyclo[4.2.0]octadiene-2,4, see cis-3,4-Dichlorocyclobutene. 5,5-Dimethoxy-l,2,3,4-tetrachlorocyclopentadiene. Hexa-chlorocyclopentadiene. Methyl tra .rl2,4-pentadienoate. A 4 l6-Steroid dienes, see 4-Phenyl-l,2,4-triazoline-3,5-dione. Tetrachlorocyclopentadienone ethylene ketal ... 

The synthesis of tropine and of its esters has been made practical because succinic dialdehyde has become easily available. Furane, now available commercially, gives on anodic oxidation in methanol with ammonium bromide as electrolyte good yields of 2,5-dimethoxy-2,5-2H-furane (37a). This mixed ketal of maleic dialdehyde could be hydrogenated readily and quantitatively over Raney nickel to 2,5-dimethoxy-4H-furane (37b). The latter as a mixed ketal of succinic dialdehyde undergoes acid hydrolysis easily. Optimum conditions for the condensation of this dialdehyde formed in situ to tropinone have been recorded (38) with yield up to 93% and at a higher rate than described earlier (18). 

AI3-16096 Anesthenyi Bis(methoxy)methane Dimeth-oxymethane Dimethyl formal 2,4-Dioxapentane EINECS 203-714-2 Formal Formaldehyde dimethyl-acetal Formaldehyde methyl ketal HSDB 1820 Methane, dimethoxy- Methoxymethyl methyl ether Methylal Methylene dimethyl ether Metylal UN1234, Used as a solvent In organio synthesis perfumes, adhesives, protective coatings special fuel. Liquid mp = -104.8° bp = 42° d = 0.8593 soluble in H2O (30 g/100 ml), very soluble In EtOH, Et20, MezCO, CeHe LD50 (rbt orl) n5708mg/kg. 

Benzil dimethyl acetal Benzil dimethyl ketal Benzil mono(dimethyl acetal) Benzil mono(dimethyl ketal) a,a-Dimethoxy-a-phenylacetophenone a,a-Dimethoxy-deoxybenzoin 2,2-Dimethoxy-1,2-diphenylethan-1-one 2,2-Dimethoxy-1,2-... 

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