Acetals ethers, synthesis

Picolyl ethers are prepared from their chlorides by a Williamson ether synthesis (68-83% yield). Some selectivity for primary versus secondary alcohols can be achieved (ratios = 4.3-4.6 1). They are cleaved electrolytically ( — 1.4 V, 0.5 M HBF4, MeOH, 70% yield). Since picolyl chlorides are unstable as the free base, they must be generated from the hydrochloride prior to use. These derivatives are relatively stable to acid (CF3CO2H, HF/anisole). Cleavage can also be effected by hydrogenolysis in acetic acid. ... 

Koenigs-Knorr reaction of, 990 molecular model of, 119, 126, 985 mutarotation of, 985-986 pentnacetyl ester of, 988 pentamethyl ether of, 988 pyranose form of, 984-985 pyruvate from. 1143-1150 reaction with acetic anhydride, 988 reaction with ATP, 1129 reaction with iodomethane, 988 sweetness of. 1005 Williamson ether synthesis with. 988... 

Tumor necrosis factor inhibition. Ethanol (95%) extract of the rhizome, in cell culture at a concentration of 100 pg/mL, was inactive on macrophage cell line RAW 264.7 vs EPS induction of TNF-az° zp Tumor promotion inhibition. Ethyl acetate and methanol extracts of the dried rhizome, in cell culture at a concentration of 50 pg/mL, produced weak activity on G3H/ lOTl/2 cells vs tetradecanoyl phorbol acetate-induced acetate phospholipid synthesis. The hexane extract was inactiveZ . Ethanol (95%) and petroleum ether extracts of the dried rhizome, in cell culture at a concentration of 160 and 80 pg/mL, re-... 

O-protected cyclic or acyclic carbon frameworks. The choice of acetals or ethers as derivatives allows a systematic manipulation of diols and polyols. Kinetic control and a lesser affinity for protonation on sulfur compared with oxygen allows the transformation of cyclic hemiacetals into acyclic dialkyl dithioacetals. Acetal, ether, and dithioacetal derivatives are some of the pivotal intermediates needed to explore various applications of carbohydrates in synthesis. 

Figure 12.25 shows how acetals can be brominated electrophihcally because of the (weakly) acidic reaction conditions. Proper acidity and electrophihcity is ensured by the use of pyri-dinium tribromide (B). This reagent is produced from pyridinium hydrobromide and one equivalent of bromine. Pyridinium tribromide is acidic enough to cleave the acetal A into the enol ether G. This cleavage succeeds by way of an El elimination like the one encountered in Figure 9.32 as an enol ether synthesis. The enol ether G reacts with the tribromide ion via the bromine-containing oxocarbenium ion H and the protonated acetal D to form the finally isolated neutral bromoacetal C. (The reaction can be conducted despite the unfavorable equilibrium between the acetal A and the enol ether G, since G continuously reacts and is thus eliminated from the equilibrium.)... 

CHAPTER 7 CHAPTER 8 CHAPTER 10 CHAPTER 11 CHAPTER 15 CHAPTER 17 CHAPTER 18 Acid-Catalyzed Dehydration of an Alcohol 313 Electrophilic Addition to Alkenes 330 Grignard Reactions 443 The Williamson Ether Synthesis 500 The Diels-Alder Reaction 684 Electrophilic Aromatic Substitution 757 Nucleophilic Additions to Carbonyl Groups 841 Formation of Imines 851 Formation of Acetals 856... 

Singular examples to form aromatic ethers are a base-catalyzed, multistep, one-pot reaction of aryl methyl ketones with the appropriate fluorinated arylidenemalonitriles, the mercury acetate assisted synthesis of pentahalophenylvinyl ethers from vinyl acetate and the corresponding phenol, and the radical displacements in aryloxycyclohexadienones (e.g., 27) by halophenols. 2,3-Dichloro-5,6-dicyanohydroquinone (28) and products such as 29 are readily formed when cyclohexadienone 27 is treated with different phenols. 

The methylthiomethyl ether (MTMOR) Tertiary hydroxyl groups, which are susceptible to acid-catalyzed dehydration, can be easily protected as MTM ethers and recovered in good yield. The MTM ether of a hydroxyl group can be formed either by a typical Williamson ether synthesis or on reaction with dimethylsulfoxide (DMSO) and acetic anhydride (AC2O). In the latter case, the reaction proceeds with the Pummerer rearrangement " (Scheme 1.25). 

Cyclopropanols can be converted to various cyclopropyloxy derivatives (esters, e.g. acetates, ethers, e.g. methyl and ethyl ethers, and acetals, e.g. tetrahydropyran-2-yloxy derivatives) under the appropriate reaction conditions. In most cases the synthesis of cyclopropyl esters by the reaction between a cyclopropanol and an acid chloride (e.g. formation of 1 ) or acetic anhydride (e.g. formation of 2 ) have been reported. The yields were particularly good (84-95%) when acetic anhydride was used, although a drawback of the reaction can be byproduct formation. When a reactive moiety is attached to the cyclopropane ring in addition to the hydroxy group, other reactions can also occur m-l-(aminomethyl)-2,2-dimethyl-3-(2-methylprop-l-enyl)cyclopropanol (3) reacted with phosgene in benzene to give the corresponding carbamate l,l-dimethyl-2-(2-methylprop-l-enyl)-4-oxa-6-azaspiro[2.4]heptan-5-one (4) in 31% yield. ... 

Onium Ions. Trialkyloxonium ions (R O A ) became the conventional initiators for the cationic ring-opening polymerization of all classes of heterocycles (cyclic acetals, ethers, sulfides, lactones, phosphates, and amines). They are prepared by two methods developed by Meerwin (38) and Olah (39). Another more general and convenient synthesis method was recently developed by Penczek et aL (40) ... 

The synthesis of block copolymers by sequential polymerization requires a living polymer prepared from the less nucleophilic monomer (first block) and the addition of a more nucleophilic monomer to the active species located on this first block. The general order of nucleophilicities of heterocyclic monomers is as follows Siloxanes orthoesters < acetals < ethers < sulfides < oxazolines < amines. Depending on substitution and ring strain some changes may occur in these positions. 

In Fig. 5.28a experimental and simulated rates for the synthesis of MTBE from methanol and isobutene are depicted, which show that the rate expression (5.63) is valid for the MTBE synthesis [45]. Fig. 5.28b illustrates its validity for the ETBE synthesis from ethanol and isobutene [41] compared with experimental data reported by Francoisse and Thyrion [47]. In analogous manner this rate approach can be applied to the synthesis of the fuel ether TAME from methanol and isoam-lyenes [43, 46]. Activity-based rate expressions were also applied for other reactions carried out in strongly non-ideal liquid mixtures, for example for butyl acetate synthesis [48] and for dimethyl ether synthesis [49]. 

Synthesis of Butyric and Caproic Ethers from Acetic Ether Proc. Roy. Soc., 1865, xiv, 198-204 (received 5 April 1865). 

Synthetical Researches on Ethers. No. i. Synthesis of Ethers from Acetic Ether Phil, Trans.y 1866, clvi, 37-72 (received 13 July, read 18 November 1865) Ann.y 1865, cxxxv, 217 (August) y. Chem. Soc.y 1867, xx, 102-16. 

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