Other Acetals

A convenient synthesis for methylene acetals of different carbohydrates using dibromomethane potassium hydroxide in DMSO at room temperature has been described. Kinetic acetalatlon of 8-nethoxycarbonyloctyl-tfi-D-mannopyranoside with 1-ethoxycyclohexene gave the 4 6-cyclohexylidene derivative (17). The photocyclization of 3-oxobutyl mannopyranosides (18) and (19) yielded the /S-spiroacetals (20) and (21), whose structures were determined by n.m.r. and X-ray crystallography. 

The C-n.m.r. of methyl 3,4,- 0-(1-carboxyethylldene)-75-D-fuco-and -galacto-pyanosides is referred to in Chapter 20. Reductive cleavages of acetals are described in Chapter 4  

Liptak, J.Imre, J.Harangi, and P.Nanasi, Tetrahedron. 1982,3721. A.Liptak, V.A.Olah, and J.Kerekgyarto, Synthesis, 1982, 421. 

An improved synthesis of 1,2-0-cyclohexylidene-myo-inositol in 45 -50% yield utilized the reaction of 1,1-dimethoxycyclohexane with myoinositol in DMSO catalyzed by Nafion-H, a perfluorinated strongly acidic ion exchange resin. Minor products were the 1,2 3 4- 1 2 4,5- and 1,2 5t6-diacetals. The acidic reagent systems, phosphorus pentoxide-trimethylsilyl triflate and phosphorus pent-oxide-boron trifluoride etherate, have proved effective for 0-methoxymethylation of carbohydrate and nucleoside derivatives with dimethoxymethane noteworthy is the compatibility of the reagents 

The isobutylidenation of acyclic polyols with methyl ethyl ketone, either in DMF with catalytic H2SO4 or without cosolvent and with / -TsOH as catalyst, has been examined. Highly crystalline l,2 3,5-di-0-cyclohexylidene-a-D-xylofuranose has been isolated in high yield on treatment of the crude xylose syrup obtained from corncobs with cyclohexanone and sulfuric acid in diethyl ether. Hydroxyethyli-dene acetals of D-threitol, used as building blocks in the synthesis of supramole-cular host systems, are referred to in Chapter 24. 

A protocol for the reliable and reproducible preparation of 4,6-0-benzylidene-D-glucopyranose in 72% yield, employing benzaldehyde dimethylacetal and TsOH in DMF, and new, corrected physical data for this compound and its crystalline 1-O-sodio derivative (thought to be the P-anomer) have been reported. Rapid and efficient benzylidenation of acid sensitive substrates has been 

Cyclitols and symmetrical acyclic polyols have been desymmetrized by fonnation of dispoke adducts such as myo-inositol derivative 7.  

The multi-step syntheses of disaccharide 8 and similar pyruvated saccharide fragments related to the aggregation factor of a marine sponge involved introduction of the pyruvate acetal groups without glycosidic bond cleavage by use of methyl pyruvate in the presence of BF3 etherate without added solvent.  

Reagents i, MeC(0)CH20Ac, TmsOTf, TfOH ii, EtsN, aq. MeOH Swern oxidation iv, Br2, MeOH 

Four oleanolic acid glycosides (e.g.. glucoside 23) with unusual acidic acetal moieties have been isolated from Beta vulgaris (sugar beet).  

An efficient one-pot procedure for removal of 4,6-O-ethylidene groups from D-galactopyranose residues in hetero-oligosaccharides has been described, involving acetolysis, followed by hydrolysis and acetylation.  

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Copper acetate, ferrous acetate, silver acetate [563-63-3] basic aluminum acetate, nickel acetate [373-02-4] cobalt acetate, and other acetate salts have been reported to furnish anhydride when heated. In principle, these acetates could be obtained from low concentration acetic acid. CompHcations of soHds processing and the scarcity of knowledge about these thermolyses make industrial development of this process expensive. In the eady 1930s, Soviet investigators discovered the reaction of dinitrogen tetroxide [10544-72-6] and sodium acetate [127-09-3] to form anhydride ... 

The LC q (lowest possible lethal concentration) has been reported to be 23 ppm for a 30 min exposure time (mouse), 53 ppm for an exposure time of 100 min (rat, rabbit, and guinea pig), and 200 ppm for an exposure time of 10 min (monkey). No toxic effects were reported upon exposure to 1 ppm for 7 h/d over 55 days. The oral LD q (rat) of ketene is 1300 mg/kg, the low level of toxicity probably being due to the almost immediate formation of acetic acid and other acetates in the digestive tract. 

Bu3SnOMe, CICH2CH2CI, 1 h, 77% yield.These conditions selectively cleave the anomeric acetate of a glucose derivative in the presence of other acetates. 

A good way to think about resonance forms is to realize that a substance like the acetate ion is no different from any other. Acetate doesn t jump back and forth between two resonance forms, spending part of the time looking like one and part of the time looking like the other. Rather, acetate has a single... 

Various methylene derivatives of spiroorthocarbonates and spiroorthocstcrs have been reported to give double ring-opening polymerization e.g. Scheme 4.36). Like the parent monocyclic systems, these monomers can be sluggish to polymerize and reactivity ratios are such that they do not undergo ready copolymerization with acrylic and styrenic monomers. Copolymerizations with VAc have been reported.170 These monomers, like other acetals, show marked acid sensitivity. 

M. A. Brook and T. H. Chan, Synthesis 201 (1983) fora similar use ofTMSCl in the facile preparation of ethylene ketals and other acetals, sec T. H. Chan, M. A. Brook and T. Chaly, Synthesis 203 (1983). 

The simple cleavage of lactones 1 or 2 with alcohol and acid has not been reported. However, when 1 is treated with benzaldehyde diethyl acetal and hydrochloric acid, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (47) is formed in >90% yield.77,78 No other isomers were observed, and other acetals of benzaldehyde, as well as aliphatic aldehydes, afford similar products in good yield.77 D Addieco prepared36 similarly protected derivatives of L-gulonic acid by oxidation of l,3 2,4-di-0-ethylidene-D-glucitol (15), followed by esterification of the resulting acid with diazomethane. 

Acetic acid is an important bulk commodity chemical, with world annual production capacity of ca. 7 million tonnes. The principal use (ca. 40%) of acetic acid is in the manufacture of vinyl acetate, a monomer of great importance in the polymer industry. A variety of other acetate esters are also... 

Other acetal-type protecting groups (tetrahydrofurfuryl ethers, methoxymethyl ethers, 1,3-dioxolanes) are also considered to be incompatible with oxidising agents. 

Acetals and ketals are very important protecting groups in solution-phase synthesis, but only a few constructs have been used as linkers in solid-phase synthesis (Tab. 3.3). The THP-linker (22) (tetrahydropyran) was introduced by Ellman [54] in order to provide a linker allowing the protection of alcohols, phenols and nitrogen functionalities in the presence of pyridinium toluene sulfonate, and the resulting structures are stable towards strong bases and nucleophiles. Other acetal-linkers have also been used for the attachment of alcohols [55, 56]. Formation of diastereomers caused by the chirality of these linkers is certainly a drawback. Other ketal tinkers tike... 

Analyses of the pheromone glands of the kvoAcAnadevidiapeponis and Maddunnoughia confusa, showed that A. peponis produces six monoene acetates and two monoene alcohols and that M. confusa produces five monoene acetates. These components include (2 )-7-dodecenyl acetate as a major common constituent and three other acetates as minor common constituents. The minor constituents are quite different in blend composition. An indispensable component for male attraction is (Z )-5-decenyl acetate... 

The THP group, like other acetals and ketals, is inert to nucleophilic reagents and is unchanged under such conditions as hydride reduction, organometallic reactions, or base-catalyzed reactions in aqueous solution. It also protects the hydroxyl group against oxidation. 

Barium acetate is used as a mordant for printing textile fabrics for drying paints and varnishes in lubricating oil in the preparation of other acetates and as a catalyst in organic synthesis. 

Phenyl Meldrum s acid 243 <2007JOC1399> and other acetals, such as 244 and 245 <2006HCA991>, have been subjected to flash vacuum pyrolysis (EVP). As displayed in Scheme 11 (Section 8.11.6.1.1), acylketenes are the major products. 

Like the cWo-derivative, acetals may be formed using a similarly structured exo-annulated MBF-OH43. Conformational analysis can be carried out to determine the absolute configuration of compounds of a similar structure as with the endo-annulated reagent. Differences in chemical shift of the same hydrogens and carbons are similar and reveal that other acetals may be equally useful for enantioselectivity studies. 

The hydrolysis of acetals are reported to go smoothly.292 However, some precautions should occasionally be taken since it has been reported that treatment of cAO-2-hydroxymethyl-7,7-dimcthoxybicyclo[3.2.0]heptan-m7o-2-ol with a mixture of 3% hydrochloric acid/acetone/wa-ter (1 9 1) gave a mixture of ertafo-2-hydroxy-< .xo-2-hydroxymethylbicyclo[3.2.0]heptan-7-one (5) and 8-hydroxymethyl-2-oxabicyclo[3.3.0]oct-7-en-3-one (6) in 2 1 ratio.323 The reaction is explained by a rearrangement of an intermediate cyclobutanone hydrate, but since other acetals do hydrolyze without similar byproduct formation it seems likely that the neighboring tertiary alcohol must be involved in the rearrangement. 

While this possibility cannot be ruled out, it is not sufficient to explain the behaviour of /-butyl acetate. The hydrolysis of this ester has been studied by many authors. Some recent results for aqueous sulphuric acid at 25°C ire available from Bunton et al.56, and these data are included in Fig. 6. The plot for this ester shows a very strongly negative slope, which can be shown to be in the region of— 9 to — 10 by a plot on expanded scales. This is ail aberration from the behaviour expected by Yates and McClelland, and could arise from a breakdown of their approximations in the case of this ester, or from a factor not allowed for by them. Since all the other acetate esters used seem to behave... 

Only short comments will be given for other acetal derivatives that are less popular Chart 1 presents a list of formulae of cyclic acetals, mainly, those with five- and six-membered rings (1,3-dioxolanes and 1,3-dioxanes). Seven-membered ring acetals are omitted because they are scarcely represented in carbohydrate chemistry. The special case of spiroacetah and cydohexane-l,2-diacetal-protecting groups, which have been reported recently, will be presented in Part K. 

Dioxanes, like other acetals and ketals, are labile to dilute acid and this property has been exploited in schemes for the protection of aldehydes and ketones as well as for... 

The shrinkage of ordinary acetate fabrics, such as suit linings, is not a problem in the Micare system. Since susceptibility to shrinkage (and dye loss) increases with the degree of acetylation of the acetate fiber, the exposure of triacetate fabric to C02 should be avoided when possible. Triacetates, which are rarely encountered, can be successfully wet-cleaned. Most other acetates can be successfully processed in the Micare system, including acetate suit lining. 

Arylcycloalkenes.10 These products can be obtained by Pd-catalyzed coupling of aryl iodides and cycloalkenes (5 equiv.) in DMF containing tetrabutylammo-nium chloride and KOAc (2 equiv.) Other acetate bases are less effective. A large excess of the cycloalkene is required to effect monoarylation. 

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