Elimination of ethanol

Note i. If only one equivalent of ethyl 1ithium is used, the conversion of the bis--ether is not complete. The necessity for two equivalents can be explained by assumin g that the rates of 1,4-elimination of ethanol and subsequent 1-lithiation are comparable. 

However, the ethoxy group of l-ethoxy-2-propylbuta-l,3-diene is no longer present. Evidently the p-toluensulphonyl eyanide (2) undergoes [4-1-2] eyeloaddition to l-ethoxy-2-propylbuta-l,3-diene (/). The resulting dihydropyridine 3 aromatises with 1,4-elimination of ethanol to form 2-p-lo y -sulphonyl-5-propylpyridine (4). 

The diethylketal of A -methylpiperidone or 3,4,5,6-tetrahydropyridines add to 4-nitrophenyl azide to give respectively compounds 113 (86CB3591) and 114 (86AP(319)1049). For compound 113 elimination of ethanol gives the tetrahy-drotriazolopyridine. 

The aminothiazole, 123, required for preparation of sulfa-thiazole (102), one of the older sulfonamides still in use, is available directly from the reaction of 1,2-dichloroethoxyethane with thiourea. The intermediate, 122, is not observed, as elimination of ethanol is spontaneous under the reaction conditions. 

Step A Ortho-Trif/uoromethy/anilinomethy/ene Ethyl Malonate - A mixture of 54.8 grams of ortho-trifluoromethylaniline and 73.5 grams of ethoxymethylene ethyl malonate was heated to 120°C under an inert atmosphere and maintained for 1 hour at this temperature while distilling off the ethanol formed. The mixture was cooled and the elimination of ethanol was completed by distillation under reduced pressure. The mixture was cooled to obtain 115 grams of ortho-trifluoromethylanilinomethylene ethyl malonate which was used as is for the following stage. A sample of the product was crystallized from petroleum ether (8P = 65° to 75°C) to obtain a melting point of 94°C. 

Diels-Alder cycloaddition of 3,4-bis(trifluoromethyl)furan with ethyl propynoate involved addition of two a,/3-unsaturated esters followed by acid-catalyzed ring opening, rearrangement, and elimination of ethanol to give a 6,7-bis(trifluoromethyl)isocoumarin-3-carboxylate [92JFC(56)359]. 

After oral ingestion, ethanol pharmacokinetics must take into account (1) Absorption from the gastrointestinal tract. Since ethanol is absorbed most efficiently from the small intestines, the rate of gastric emptying is an important factor that governs the rate of rise of blood alcohol concentration (BAC), i.e., the slope of the ascending limb of the BAC-time curve, and the extent of first pass metabolism of ethanol by the liver and stomach. (2) Distribution of ethanol in the body. Ethanol distributes equally in total body water, which is related to the lean body mass of the person, and (3) the elimination of ethanol from the body, which occurs primarily by metabolism in the liver, first to acetaldehyde and then to acetate [7]. 

A reported procedure based on lithium diisopropylamide induced double elimination of ethanol from bromoacetaldehyde diethyl acetal also was not very effective for the large scale preparation of phenylthioacetylene.8 Another more recent synthesis of the title compound relies on the reaction of dimethyl(chloroethynyl)carbinol with an alkali metal phenylthiolate, followed by... 

Few examples of the preparation of six-membered heteroaromatic compounds using Fischer-type carbene complexes have been reported [224,251,381]. One intriguing pyridine synthesis, reported by de Meijere, is sketched in Figure 2.35. In this sequence a (2-aminovinyl)carbene complex first rearranges to yield a complexed 1 -azadiene, which undergoes intermolecular Diels-Alder reaction with phenylacetylene. Elimination of ethanol from the initially formed adduct leads to the final pyridine. 

Attempted iodocyclization with iodine in moist acetonitrile of ethyl 2-hydroxypent-4-enoate (59) to give the iodotetrahydrofuran (62) gave instead a 2 1 mixture (80%) of syn- and -lactones (60) and (61). Labelling studies with H2 0 indicated that the probable mechanism of the reaction involved initial attack of the ester group upon the iodonium ion (63) to yield a mixture of epimeric carbocations (64), which upon attack by water would yield the orthoesters (65), elimination of ethanol from which giving the epimeric y-lactones (60, 61). ... 

In sharp contrast with the remaining transition metals, Group 6 allenylidenes [M (=C=C=CR R )(C0)5] (M = Cr, Mo, W) containing non-donnor substituents at Cy are in general thermally unstable [11-15]. For this reason, most of the reported examples are substituted derivatives bearing heteroatomic Ti-donor groups [9]. In this sense, the first stable Group 6 allenylidenes reported in the literature were the amino-allenylidene complexes 2, prepared by E. O. Fischer and coworkers by a Lewis-acid induced elimination of ethanol from the 3-dimethylamino-l-ethoxy-3-... 

The imidates (62) also serve as nitrile yhde synthons via cycloaddition and subsequent spontaneous elimination of ethanol (34,35). Cycloadditions were carried out to aldehydes, leading to 2-oxazolines (e.g., 64) and to isocyanates and isothiocyanates. In the preparation of the 2-oxazolines, a solvent-less mixture of the imidate and the required aldehyde were heated at 70 °C and the cycloadducts 64 (R=Ph, 2-furyl, Mc2CH, 2-HO C6H4, 2-pyridyl, cinnamyl) were isolated in yields of 64—91%. 

An analogous transformation can be achieved thermally using [l,2,3]triazolo[4,5- pyrimidine bearing an ethoxy-carbonylhydrazino substituent at the 7-position, which induced a cyclization with the elimination of ethanol (Scheme 34) <1999JHC1195>. 

A more recent synthesis of [l,2,3]triazolo[4,5-r7lpyrimidin-7-ones involved the elimination of ethanol from a base-catalyzed cyclization of a 5-urea derivative onto the 4-ester substituent of, for example, guanidine 71 (Scheme 49) <2005S2544>. 

Alkynyl ethers, RCH2C CCH2OR and CHjGaCCHCRlOR, are converted into 3,1 -en-ynes by treatment with sodamide in liquid ammonia. The reactions may be visualized as 1,4-eliminations of ethanol and subsequent metailanon of the intermediary cumulenes [143] ... 

The elimination of methanol, ethanol, or acetic acid is useful for the preparation of 4f/-pyrans, provided that the products exhibit sufficient stability. Thus the thermolyses of 2-ethoxy- and 2-acetoxy-2, 3-dihydro-4//-pyrans 265 undoubtedly led to unsubstituted 4//-pyran (5),18,293 but only when R = Ac was it possible to separate the unstable product 5 from reaction mixtures by GLC in 15 to 30% yields.18 Analogously, 25% of air-sensitive 2-methoxy-2//-pyran (267) was obtained on heating 266 with aluminum tri-butoxide under a nitrogen atmosphere at 155°C.33 A general technique for the preparation of condensed 4//-pyrans from their 2-ethoxy-2,3-dihydro derivatives is based on the elimination of ethanol in the presence of p-toluenesulfonic acid or polyphosphoric acid at decreased pressures293 to give... 

Treatment of methyl 4-0-ethyl-3-0-methyl-/3-D-threo-pento-sidulose (70), a model compound having a carbonyl group at C-2, with sodium 1-propoxide in 1-propanol resulted131 in quantitative elimination of ethanol and the formation of methyl 4-deoxy-3-0-methylpent-3-enosid-2-ulose (71). On further mild hydrolysis of this and related compounds, the substituents at C-l and C-3 were released (see Scheme 10).132... 

Acyloins undergo nucleophilic addition to /3-ethoxyvinylphosphonium salts (141) to yield an ylide (142) (74JOC584). Intramolecular Wittig reaction results in formation of the dihydrofuran (143), which is converted to the furan (144) by elimination of ethanol (Scheme 32). Symmetric acyloins give one product, but unsymmetrical ones may give two products under basic conditions due to tautomerization. 

In the case of the gem diester (121), the major pathway results in aromatization of the dihydropyran ring with production of the pyrylium species (121a). This is derived from the [M - C02Et]+ ion with subsequent loss of carbon monoxide and elimination of ethanol. It was shown that RDA fragmentation of (121), a minor pathway only, is a thermally induced process (72CJC1539). 

In the 1,4-benzoxathiane series, neither dehydration of the hydroxy compound (189) nor elimination of ethanol from (190) give very satisfactory yields of (184) and once again the best yield (76%) is obtained by pyrolysis of the 2-acetoxy derivative (191). 3-MethyI-l,4-benzoxathiin is obtained by an analogous route, but 2,3-diphenyl-l,4-benzoxathiin is conveniently prepared by a one-step condensation of 2-mercaptophenol and benzoin in 21% yield <66HC(21-2)852>. 

Michael addition products, the ethoxycyclopropyl analogue gave also the allenyli-denechromium complex resulting from the elimination of ethanol. 

The elimination of ethanol seems to start with deprotonation of the a-position of the pyrrole 54 under the action of superbase. The carbenoid intermediate 62 formed is then reduced (Scheme 32). The reducing properties of the KOH/DMSO system have been observed (88KGS350). 

Carbomethoxypivaloylketene 733 can undergo a hetero-Diels-Alder reaction with ethoxyalkyne to yield methyl 2-fer/-butyl-6-ethoxyM-oxoM//-pyran-3-carboxylate (Equation 292). Likewise, carbomethoxypivaloylketene 733 undergoes a hetero-Diels-Alder reaction with ethoxyethene to afford the intermediate dihydropyran-4-one, which upon elimination of ethanol affords methyl 2- v/-butylM-oxo-4//-pyran-3-carboxylate (Scheme 185) <2001T6757>. 

As previously described, the 3//-pyrrolium adduct 50 is obtained from the TBSOTf-promoted aldol reaction between the 1-methylpyrrole complex 21 and acetaldehyde diethylacetal (Figure 11). Deprotonation of 50 occurs at C-3 with i-Pr2EtN to give the corresponding -substituted lH-pyrrole complex. Addition of triflic acid results in the elimination of ethanol to give the azafulvenium complex 141 as a 3 2 mixture of diastereomers (Figure 25). Deprotonation of 141 results in formation of the unstable unsubstituted P-vinylpyrrole complex 142, which can be trapped in situ with N-phenyl maleimide (vide infra). 

Then the reactivity of the tetracarboxylic acid-based salt monomers was compared with that of the salts consisting of tetracarboxylic acid half diesters. The P-XPM series polyimides were prepared by the high-pressure polycondensation of salt monomers XPME derived from the aliphatic diamines and pyromellitic acid half diethyl ester (see Eq. 5, Ar=PM and R=ethyl) [20], in addition to the polymers obtained from the pyromellitic acid-based salt monomer XPMA [24] already shown in Table 1. The polycondensation of salts XPME proceeded readily under high pressure of 250 MPa at 240 °C for 15 h, even with the elimination of ethanol and water as the by-products in the closed reaction vessel, and this afforded the polyimides with inherent viscosities up to 1.6 dL/g. Therefore, the reactivity of salt monomers XPME was found to be almost comparable to that of the parent salt XPMA, and the properties of the resultant P-XPM series polyimides from XPME were the same as those obtained from salts XPMA. 

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