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Acetale

Based on the above-mentioned stereochemistry of the allylation reactions, nucleophiles have been classified into Nu (overall retention group) and Nu (overall inversion group) by the following experiments with the cyclic exo- and ent/n-acetales 12 and 13[25], No Pd-catalyzed reaction takes place with the exo-allylic acetate 12, because attack of Pd(0) from the rear side to form Tr-allyl-palladium is sterically difficult. On the other hand, smooth 7r-allylpalladium complex formation should take place with the endo-sWyWc acetate 13. The Nu -type nucleophiles must attack the 7r-allylic ligand from the endo side 14, namely tram to the exo-oriented Pd, but this is difficult. On the other hand, the attack of the Nu -type nucleophiles is directed to the Pd. and subsequent reductive elimination affords the exo products 15. Thus the allylation reaction of 13 takes place with the Nu nucleophiles (PhZnCl, formate, indenide anion) and no reaction with Nu nucleophiles (malonate. secondary amines, LiP(S)Ph2, cyclopentadienide anion). [Pg.294]

Cyclic Acetals. One of the most significant developments in the chemistry of sucrose was the synthesis of cycHc acetals which, despite many attempts, were not synthesized until 1974. The first synthesis of 4,6-0-benzyhdenesucrose was achieved from the reaction of sucrose with a, a-dibromotoluene in pyridine (29). Since then, many new acetalating reagents have been used to give a variety of sucrose acetals, generally by transacetalation reactions. [Pg.33]

Acetalation. As polyhydroxy compounds, carbohydrates react with aldehydes and ketones to form cycHc acetals (1,13). Examples are the reaction of D-glucose with acetone and a protic or Lewis acid catalyst to form l,2 5,6-di-0-isoprop5lidene-a-D-glucofuranose [582-52-5] and its reaction with benzaldehyde to form 4,6-0-benzyhdene-D-glucopyranose [25152-90-3]. The 4,6-0-(l-carboxyethyhdine) group (related to pymvic acid) occurs naturally in some polysaccharides. [Pg.481]

As already noled, lower order cyanocuprates are more Su2 -selective reagents. On irealmenl widi acetale 163, however, a mixture of tlie iwo regioisomets was oblained fetilry 2) [81]. In addih on, y-alkylalion bad taken place witli ca. 2 596 loss ... [Pg.212]

In a related study the adduct of the lithium enolate of methyl bis(trimethylsilyl)acetale and ( —)-(/J)-2-(4-methylphenylsulfinyl)-2-cyclopentanone was transformed to ( — )-methyl jasmonate in > 99% ee. In contrast to the previous study described in this section, addition of the enolate proceeded apparently through a chelated form of the enone15. [Pg.1046]

Acetale zu Athem (S.430), die weiter zu Alkanen gespalten werden konnen (S.413)... [Pg.11]

Es reduziert Carbonsauren zu Kohlenwasserstoffen9 (s.S. 171 f.), Carbonsaureester (S. 219), Lactone (S. 225f.) und Acetale (S. 434) zu Athern. Auch Halogen-alkane werden hydriert (S. 393). [Pg.32]

Bei der Reduktion von Oxo-carbonsaureestern mit Natriumboranat werden unter ge-eigneten Bedingungen semicyclische Acetale gebildet3 ... [Pg.195]

Cyclische N-Acyl-amidine werden dagegen mit guten Ausbeuten iiber die N,N-Acetale zu Aminen gespalten z. B.5 ... [Pg.352]

Aus methodischen Griinden werden auch die Stickstoff-Analogen der Acetale, die sich besonders Ieicht reduzieren lassen, hier behandelt. [Pg.408]

Acetale werden von Lithiumalanatin der Regel nicht angegriffen, so daB sie als ge-schiitzte Formen von Aldehyden und Ketonen5 besonders in der Zucker-Chemie dienen konnen6,7. [Pg.429]

Acetale mit bestimmten strukturel len Merkmalen, z. B. von Chinonen8, von halogcnierten o-Diphenolen9 und von c. wcyclischen Ketonen mit elektronenanziehenden Gruppen (Isatinen)10 werden durch Lithiumalanat... [Pg.429]

Acetale konnen durch elektrophile Hydride in den meisten Fallen reduziert werden, aus acyclischen Acetalen werden Ather und Alkohole, aus cyclischen tu-Hydroxy-ather erhalten. Der erste Schritt, der durch Lewis-Sauren katalysiert wird, ist auch hier die Bil-dung des entsprechenden Carbcnium-Ions (s.S. 409). Die Methode ermoglicht die einfa-che Herstellung von Athern aus Aldehyden und Ketonen. [Pg.430]

Bis-[2-methyl-propyl]-aluminiumhydrid reduziert Acetale ohne Losungsmittel bei 70-80° aus cyclischen Acetalen werden Aluminiumalkanolate gebildet, die mit ver-dunnter Saure hydrolysiert werden miissen. [Pg.430]

Acetale von Alkanalen bzw. Alkanonen liefern mit Lithiumalanat/Titan(IV)-chlorid (2 1) in atherischer Losung die entsprechenden Ather in Ausbeuten von 70-90% d.Th., Acetale aromatischer Aldehyde und Ketone reagieren dagegen in Tetrahydrofuran bei 20° zu Olefinen als Kopplungsprodukten die Kopplungsreaktion tritt zuerst ein. So erhalt man z.B. aus Benzaldehyd-diathylacetal 85% d.Th. 1,2-Diathoxy-1,2-diphenyl-athan ne-ben 10% d.Th. Stilben4 ... [Pg.433]

Semicyclische 0,S-Acetale mit einer exocyclischen Thioather-Gruppe werden in-folge der leichteren Spaltbarkeit der C-O-Bindung selektiv zu tw-Hydroxy-sulfanen reduziert z.B.3 ... [Pg.435]

Cyclische 0,N-Acetale vom Typ der 1,3-Oxazolidine und 2,5-Dihydro-l,3-oxazole werden durch Lithiumalanat7 und Natriumboranat8,9 zu 2-Amino-alkoholen reduziert. Aus 3-Methyl-2-phenyl-l,3-oxazolidin wird z.B. mit Natriumboranat 2-(N-Methyl-N-benzyl-amino)-athanol (74% d.Th) erhalten8 ... [Pg.436]

Die gebildeten Acetale reagieren nicht weiter8. In semicyclischen Orthocarbonsaure-triestem wird die erocyclische Alkoxy-Gruppe abgespalten z.B.9 ... [Pg.445]

Ketone konnen tiber die Se.Se-Acetale durch Triphenyl-zinnhydrid zu Kohlenwasserstoffen reduziert werden4. [Pg.450]

S,N-Acetale werden durch komplexe Metallhydride in der Regel langsamer reduziert als die entsprechenden 0,N-Acetale. Piperidinomethyl-butyl-sulfid ergibt z.B. mit Na-triumboranat bei 20° erst nach 10 Stdn. 53% d.Th. 1 -Methyl-piperidin (Arbeitsvorschrift auf S. 437)5 ... [Pg.450]

C4 H35C1N 0 120568-18-5) see Losartan potassium tert-butyl (4R,6S)-2-(6-cyanomethyl-2,2-dimcthyl-13-di-oxan-4-yl)acetale... [Pg.2318]

The pyruvic acid may also be linked to vicinal positions. When linked to 0-3 and 0-4 of a D-galactopyranosyl residue (40), the dioxolane ring becomes cw-fused. In the limited number of known examples, the absolute configuration at the acetalic carbon atom is (S), as in 40. There are some examples of tra -fused dioxolane rings, and these are more sensitive to hydrolysis with acid than the others. Thus, pyruvic acid is acetalically linked to 0-3 and 0-4 of an a-L-rhamnopyranosyl residue in the Klebsiella type 72 capsular polysaccharide, to 0-2 and 0-3 of an a-D-galactopyranosyl residue in the Streptococcus pneumoniae type 4 capsular polysaccharide, and to 0-2 and 0-3 of a S-D-glucopyranosyluronic acid residue in the Klebsiella K1 capsular polysaccharide. " In the extracellular polysaccharide from... [Pg.305]

Klebsiella K12, pyruvic acid is acetalically linked to 0-5 and 0-6 of a y -D-galactofuranosyl residue. Pyruvic acid is further acetalically linked to 0-4 and 0-5 of a D-mannitol residue in an unusual type of teichoic acid from Brevibacterium iodinum The absolute configuration at the acetalic carbon atom is (S) in the 5. pneumoniae type 4 polysaccharide, but it has not yet been determined for the other polymers. [Pg.306]

Spaltung ungesattigter Acetale dar, iiber die eine neuere detaillierte Untersuchung franzosischer Autoren vorliegt 17>. Das allgemeine Ver- ... [Pg.81]

Total time required for acetalation/ketalation and acetylation. [Pg.65]

B. Mukhopadhyay, D. A. Russell, andR. A. Field, One-pot acetalation-acetylation of sugar derivatives employing perchloric acid immobilised on silica, Carbohydr. Res., 340 (2005) 1075-1080. [Pg.94]

B. Mukhopadhyay, Sulfuric acid immobilized on silica An efficient promoter for one-pot acetalation-acetylation of sugar derivatives, Tetrahedron Lett., 47 (2006) 4337-4341. [Pg.94]


See other pages where Acetale is mentioned: [Pg.33]    [Pg.450]    [Pg.359]    [Pg.308]    [Pg.346]    [Pg.33]    [Pg.268]    [Pg.430]    [Pg.431]    [Pg.431]    [Pg.431]    [Pg.434]    [Pg.436]    [Pg.452]    [Pg.954]    [Pg.305]    [Pg.306]    [Pg.56]    [Pg.242]    [Pg.63]    [Pg.189]    [Pg.214]   


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14-Bromocodeinone dimethyl acetale

Acetalation

Acetalation

Acetalation agents

Acetalation catalysts

Acetalation mechanism

Acetalation methods

Acetalation of Starch Derivatives

Acetalation, glucitol

Acetalation, of starch

Acetalation, selective

Acetale ketene silyl

Acetalic units

Nitro acetalation

Starch acetalation

Sugar acetalation

The Acetalation Reaction

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