Aqueous workup

The submitters observed more precipitate on dilution with ether and recommended that the aqueous workup be performed In a hood. 

The checkers found that unless the aqueous workup is cooled, the dichloromethane boils vigorously. 

Chiral oxazolines have also been utilized for the synthesis of ehiral ketones bearing quaternary earbon stereoeenters. As shown below, reaetion of substituted oxazoline 30 with 2 equiv PhLi followed by treatment with benzyl bromide gives ketone 33 upon aeidie hydrolysis. This reaetion is believed to proeeed via addition of PhLi to keteneimine 31 to afford metalated enamine 32, whieh undergoes alkylation at the nueleophilie earbon to provide 33 after aqueous workup. ... 

For the mechanistic course of the reaction the diketone 5 is assumed to be an intermediate, since small amounts of 5 can sometimes be isolated as a minor product. It is likely that the sodium initially reacts with the ester 1 to give the radical anion species 3, which can dimerize to the dianion 4. By release of two alkoxides R 0 the diketone 5 is formed. Further reaction with sodium leads to the dianion 6, which yields the a-hydroxy ketone 2 upon aqueous workup ... 

Rebeiro and Khadilkar have investigated the reactions between trichloroalkanes and aromatic compounds. For example, the benzoylation of aromatic compounds in ionic liquids was performed with benzotrichloride, giving ketones on aqueous workup [98]. 

When y-lactone 14 is treated with methylmagnesium bromide in THF at -78 °C, a carbonyl addition reaction takes place and gives, after aqueous workup, a hemiketal that is subsequently converted to... 

With Oxygen Nucleophiles Aziridine ring-opening of 111 (Scheme 3.42) with water in the presence of a catalytic amount of TsOH gave the corresponding (3-hydrox-yphenylalanine derivative 121 in 72% yield as the major isomer [74], Treatment of N-(p-tolylsulfmyl) aziridine-2-carboxylates with TFA and subsequent aqueous workup resulted in the formation of j3-substituted serine derivatives [62, 63, 101]. Under these reaction conditions, not only was the aziridine ring opened, but also the N-sulfmyl group was removed treatment of 122 (Scheme 3.43) with TFA at 73 °C, for example, afforded 123 in 75% yield [101],... 

Trapping the reaction mixture with 3.9 g (12.0 mmol) of tributyltin chloride affords, after aqueous workup and flash chromatography (silica gel, pentane/diethyl ether 20 1) a mixture of the (1Z.3/ )- and (1 ,3S)-isomers yield 2.34 g (48%). For further conversions see Section D.l.3.3.3.8.2.3. 

A mixture of 2.0 mmol of a 1.6 N solution of butyllithium in hexane and 0.47 g (2.0 mmol) of(-)-spartcinc in 10 mL of diethyl ether is stirred for 15 min at — 78 rC then 0.26 g (2.0 mmol) of 1-methyl-l//-indene in 2 mL of diethyl ether are added. Stirring is continued for 30 inin at 20 °C, the mixture is cooled to — 70 CC and 2.5 mmol of the acid chloride in 2 mL of diethyl ether are added. After stirring for 4h the usual aqueous workup was accomplished by addition of 10 mL of diethyl ether and successive washing with 10 mL of 2 N aq HC1. water and sat. aq NtiCl, respectively, followed by chromatographic purification on silica gel with diethyl cthcr/pentane. 

A solution of 1.5 mol equiv of butyllithium in hexane is added to 1.5 mol equiv of a 1 M solution of hexabutylditin in THF at 0 C under nitrogen, and the mixture is stirred for 20 min. The solution is cooled to — 78 °C and a solution of 1.5 mol equiv of diethylaluminum chloride in toluene is added. After stirring for 1 h at — 78 °C, a solution of 0.05 mol equiv of [tetrakis(triphenyl)phosphine]palladium(0) in THF is added followed by a solution of the allyl acetate in THF. The mixture is warmed to r.t., and stirred until the allyl acetate has reacted (TLC). The solution is cooled to 0°C, and an excess of aq ammonia slowly added. After an aqueous workup, the products arc isolated and purified by flash chromatography on silica gel using 1 % triethylamine in the solvent to avoid acid-induced loss of stannane. 

If no aqueous workup, but anhydrous cleavage of the reaction product 11 is performed with iodotrimethylsilane, the titanium iodide 12 can be recovered or used again in the same flask36. 

The condensation is usually carried out by adding a solution containing equimolar amounts of the allyl halide and the aldehyde or ketone to a solution of at least two equivalents of chromium-(II) chloride in THF at 0 5°C. Frequently, the less precious component is used in 50-100% excess. Although commercially available anhydrous chromium(II) chloride can be utilized (Method B), its in situ preparation from chromium(III) chloride and lithium aluminum hydride (Method A) is often preferred. The removal of chromium and aluminum hydroxide, which are formed on aqueous workup, can be accomplished by filtration in the presence of a filtration aid. 

However, deprotonation of rc-rf-butyldimethylsilyl-protected products 2 (prepared according to the classical Henry conditions )22, and consecutive reprotonation, provides the silylated nitroaldols 2 with high (R, R ) selectivity. Deprotonation of 2 by treatment with lithium diisopropylamide in tetrahydrofuran at — 78 C furnishes nitronates which are stable against / -elimination at that temperature. Protonation of these intermediates is achieved with an acetic acid/tetrahydrofuran (1 1) solution at —100 C. To achieve maximum yields, the mixture should be warmed up slowly before aqueous workup. 

The addition of tributylphosphine-stabilized alkylcopper to boron trifluoride coordinated (E)-enoatcs 4 gave, after aqueous workup, / -substituted esters in good yields and with 94-98 % de29. 

In contrast, o-(2-cyano-A-methylacetamido)nitrobenzene (38) gave 1-hydroxy-4-methyl-2,3(lH,4/7)-quinoxalinedione (40), presumably by hydrolysis of the intermediate carbonitrile (39) (NaOH, H2O, reflux, 30 min 53% or EtONa, EtOH, reflux, 30 min, aqueous workup 69%). " ... 

Ethoxycarbonylmethyl-3-(2-formylethyl)pyrazine (334) (freshly liberated from its acetal) gave a separable mixture of ethyl 6-hydroxy-5,6,7,8-tetrahydro-5-quinoxalinecarboxylate (335) its dehydration product, ethyl 7,8-dihydro-5-quinoxalinecarboxylate (336, R = Et), and the hydrolysis product, 7,8-dihy-dro-2-quinoxalinecarboxylic acid (336, R = H) [NaH, Et20, 0°C, 2 h 15%, 37%, and 37%, respectively when the aqueous workup was carried out at 0°C, product 335 predominated]. " ... 

A more synthetically reliable version of this reaction involves epoxidation of silyl enol ethers. Epoxidation of the silyl enol ethers followed by aqueous workup gives a-hydroxyketones and a-hydroxyaldehydes.144... 

The hydrolysis of Sil4.2bipy affords, after an aqueous workup, cis-bis(2,2 -bipyridine)dihydroxysilicondiiodidedihydrate, in which each of the SiOH groups is hydrogen-bonded to a water molecule only 69 (313). 

The homoallylation is applicable to multigram-scale experiments (Scheme 15) [36]. In the presence of 3mol% of Ni(acac)2, a mixture of 25 mmol of benzaldehyde, 50 mmol of Et3B, and 50 mmol of isoprene provides anti-3-methyl-l-phenyl-4-pentenol in 92% yield (4.1 g) with excellent 1,3-anti stereoselectivity. The product is purified by means of a single Kugelrohr distillation of the reaction mixture after an appropriate aqueous workup. 

As discussed previously, West and coworkers developed a two-step domino process, which is initiated by a Nazarov reaction. This can be extended by an electrophilic substitution. Thus, reaction of 1-179 with TiCl4 led to 1-182 via the intermediate cations 1-180 and 1-181. The final product 1-183 is obtained after aqueous workup in 99% yield (Scheme 1.43) [23]. It is important to mention here that all six stereocenters were built up in a single process with complete diastereoselectivity hence, the procedure was highly efficient. 

Comparison with previous FC acylations, the above processes are clean, without aqueous workup, and therefore without effluents ( green chemistry ). The graphite is, moreover, inexpensive and can be safety stored or discarded. Its activity is, however, limited to activated aromatic compounds. 

Upon standing in the dark, the solution progressively bleaches to a pale yellow solution ( 10 min), and a simple aqueous workup procedure affords crystalline 2-nitro-a-tetralone in quantitative yield. The analysis of the aqueous layer indicates the formation of one equivalent of trinitromethide according to the stoichiometry in equation (13). 

Equivalent amounts of aldehydes and alkoxytrimethylsilanes react to form unsymmetrical ethers in near quantitative yields in the presence of either trimethylsilane or triethylsilane and catalytic amounts (ca. 10 mol%) of TMSI in dichloromethane.329,333,334,341 The procedure is particularly convenient experimentally when trimethylsilane is used with TMSI because the catalyst provides its own color indicator for the reduction step (color change from deep violet to vivid red-gold) and the only silicon-containing product following aqueous workup is the volatile hexamethyldisiloxane (bp 99-100°). It is possible to introduce trimethylsilane (bp 7°) either as a previously prepared solution in dichloromethane or by bubbling it directly into the reaction mixture. Cyclohexyloxytrimethylsilane and n-butanal react by this method to give a 93% isolated yield of n-butyl cyclohexyl ether (Eq. 183).334... 

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