Formals, dialkyl

Liquid crystal polyesters are made by a different route. Because they are phenoHc esters, they cannot be made by direct ester exchange between a diphenol and a lower dialkyl ester due to unfavorable reactivities. The usual method is the so-called reverse ester exchange or acidolysis reaction (96) where the phenoHc hydroxyl groups are acylated with a lower aHphatic acid anhydride, eg, acetic or propionic anhydride, and the acetate or propionate ester is heated with an aromatic dicarboxyHc acid, sometimes in the presence of a catalyst. The phenoHc polyester forms readily as the volatile lower acid distills from the reaction mixture. Many Hquid crystal polymers are derived formally from hydroxyacids (97,98) and thein acetates readily undergo self-condensation in the melt, stoichiometric balance being automatically obtained. 

A high yield synthesis involving formal oxidation of a sulphoxide to a sulphoximine has been reported183 using O-mesitylenesulphonyl hydroxylamine (NH2OMes) (equation 67). The reaction is successful for a wide range of sulphoxides including dialkyl, diaryl and cyclic species. 

Thermolysis of the Rti(IV) dialkyl or diaryl porphyrins M(Por)R2 at 100 C in benzene leads to loss of one of the axial lieands and formal reduction of the... 

Symmetrical triazines, although not formally unsaturated, in the presence of the dialkyl phosphites undergo ring opening and selfcatalysis for Pudovik-type addition.318-322 An example is shown in Equation 3.19. 

Also in 2009, an elegant combination of two original van Leusen reactions was reported, leading to a MCR toward 4,5-disubstituted oxazoles (19) [136]. The MCR involves the base-induced mono-alkylation of TosMIC (8a) followed by the formal cycloaddition with an aldehyde (Fig. 9). Although dialkylation is a problem often... 

Of the five dialkyl peroxides with enthalpy of formation data, only those of unquestioned accuracy, dimethyl, diethyl and ferf-butyl peroxide, are included in the analysis. The enthalpies of the formal hydrogenolysis reaction 6 are remarkably consistent for the methyl, primary and tertiary compounds -335.0 2.9 kJmoR for the liquid (using the estimated enthalpy of vaporization for dimethyl peroxide) and -279.5 3.5 kJmoR for... 

As was the case for the alkyl hydroperoxides in reaction 4, the enthalpies of the oxy-gen/hydrocarbon double exchange reaction 8 for dialkyl peroxides are different depending on the classification of the carbon bonded to oxygen. For R = Me, Et and f-Bu, the liquid phase values are —4, 24.6 and 52.7 kJmoR, respectively, and the gas phase values are 0.1, 25.7 and 56.5 kJmoR, respectively. For the formal deoxygenation reaction 9, the enthalpies of reaction are virtually the same for dimethyl and diethyl peroxide in the gas phase, —58.5 0.6 kJ moR. This value is the same as the enthalpy of reaction of diethyl peroxide in the liquid phase, —56.0 kJ moR (there is no directly determined liquid phase enthalpy of formation of dimethyl ether). Because of steric strain in the di-ferf-butyl ether, the enthalpy of reaction is much less negative, but still exothermic, —17.7 kJmol (Iq) and —19.6 kJmol (g). 

Ketenedithioacetals (1) can formally be considered as S.S-dialkylated dithioacids. However, their reactivity pattern is quite different from that displayed by compounds like dithioacids and dithioesters bearing a thiocarbonyl group, and their syntheses and properties are usually treated apart. The review by Kolb [59] and its 254 references give access to most of the literature in the field (see also [60]). a-Oxoketenedithioacetals (2) are particularly versatile compounds as three-carbon synthons in organic synthesis, and some reviews deal specifically with them [61, 62]. Many efficient procedures are available for their syntheses [59, 61], and number of these make use of the reactions of carbon disulfide with carbanionic species followed by alkylation at the sulfur atoms (see [63] and [64] for the reactions of CS2). 

The primary examples of this class of compounds are the 1,2-dialkylcycloalkenes (24 n, R1, R2). The simplest thermochemical comparison we can make is with the corresponding unsubstituted cycloalkene, i.e. R1 = R2 = H. A suitable probe of the effect of the dialkylation is the enthalpy of the formal transalkylation reaction... 

Stable esters coming formally from alkynols and carboxylic, sulphonic or dialkyl phosphoric acids were prepared for the first time via alkynyliodonium salts with the corresponding anion. Several alkynyl carboxylates were obtained by anion exchange of alkynyl iodonium tosylates the initially formed salts, PhI+C=CR RCO2, were converted spontaneously into the esters on elution through a chromatographic column packed with an anion-exchange resin (Pol+ArCOj) ... 

The doubly bidentate bridging ligands (L10,11)2 are formally obtained by template coupling of two dialkyl malonate monoanions with oxalyl chloride and spontaneous double deprotonation of the bis(enol) intermediates (Scheme 10). 

Of more specialized interest is the reaction of alkynes with Co2(CO)s in polar solvents under conditions of elevated temperature and CO pressure. The major products are the (E) and (Z) isomers of so-called bifurandiones, the products of formal (but not actual) carbene dimerization. An intermediate, a complex of this lactone-derived carbene bridging a Co2(CO>7 moiety, may be isolated from reactions of alkyl-, aryl- or dialkyl-acetylenes with Co2(CO)8. Its formation is completely regioselective even for ethyl vj. methyl, placing the larger group a to the lactone carbonyl. - In the subsequent formation of the bifurandione itself regioselectivity in alkyne incorporation into the second ring is incomplete and in the opposite direction, an observation which remains unexplained (Scheme 11). ... 

Generally speaking, the spectral properties of the heterosapphyrins resemble those of the pentaaza parents . That is to say, each of these species displays intense Soret- and Q-bands that are red-shifted relative to those of the porphyrins. For instance, when one, two, or even three of the pyrrolic subunits of sapphyrin is formally replaced by a 3,4-dialkyl furan (as in 5.74-5.76), the absorption spectrum is relatively unaffected (Xmax for the free-base form is ca. 450 nm as compared to the max value of 445 nm for typical decaalkyl sapphyrins such as 5.21). Treatment of these oxasapphyrins with an acid such as HCl or HBr has only a minimal effect on the location of the Soret band it is also found at ca. 450 nm in the case of these protonated systems. 

The formal addition of an alkyl halide (RX) to the C=C double bond of the Michael acceptors proceeded in a one-pot process by initial 1,4-addition of the dialkyl aluminum chloride and subsequent trapping of the enolate intermediate with A -halosuccinimides [148]... 

Whereas palladium(0)-catalyzed reactions of dialkyl fumarate and dialkyl maleate yield reaction products identical to those obtained from the phosphane-modified nickel-catalyzed reactions (vide supra), analogous palladium(0)-catalyzed reactions with ( )-but-2-enoic or (E)-cinnamic acid derivatives lead to different products to the nickel-catalyzed reactions, i.e. in the palladium-catalyzed reactions formal distal cleavage of but-2-enoic MCP occurs to provide methyl tra i-2-methyl-4-methylenecyclopentanecarboxylate (12, R = Me) and methyl trans-4-methylene-2-phenylcyclopentanecarboxylate (12, R = Ph), respectively." Yields and stereoselectivities are slightly higher with palladium(O) catalysts. When R = Me, 7.4% of the C-C double bond isomerization product, methyl traM -2,4-dimethylcyclopent-3-enecarboxylate (13, R = Me), is additionally obtained, raising the combined yield of cyclocodimers to 49.9%. With methyl (jE )-cinnamate, analogous isomerization only occurs upon workup, i.e. distillation of the crude product. 

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