Acetylation, in situ

Potable water and raw source water Sample acetylated in situ by addition of acetic anhydride, solvent extracted and concentrated alternatively, extracted acidic sample derivatized by pentafluorobenzyl bromide and cleaned up by column chromatography HRGC-ECD (for pentafluorobenzyl derivative) HRGC-MS (for acetyl derivative) <50 ng/L (pentafluorobenzyl) <50 ng/L (acetyl derivative) 10-64% (pentafluorobenzyl derivative) 70-132% (acetyl derivative) Sitholeetal. 1986... 

Conditions for the optimization of SPME of phenol and chlorophenol soil contaminants were investigated end analysis was by GC-FID. The method was applied to soil analysis after acute contamination in industrial sites. The method was validated by comparison with an EPA certified extraction method . Soil samples were suspended in water and the extracted phenols were acetylated in situ with acetic anhydride in the presence of potassium bicarbonate. Acid was added after the end of the derivatization and SPME was performed by placing a poly(dimethylsiloxane) fiber in the headspace. End analysis was performed by introducing the fiber into the injector of a GC-MS apparatus. LOD was in the sub-ppm range, with good precision, sensitivity and linearity . ... 

The reduction of the C-a-nitro function of new nitro-S-thiodisaccharide was performed in the same fashion as described by us earlier (3) with sodium borohydride/cobalt chloride complex. For the purpose of purification and isolation, the corresponding amino derivatives were acetylated in situ and selectively deprotected to free amino derivatives at C-2 by employing Hanessian methodology 26) using triethyloxonium fluoroborate. 

Condensation of D-ribonolactone (698) with 2-(3,4-methylenedioxy-phenyl)ethylamine (697) gave an amide 699, whose acetylation with AC2O in pyridine and subsequent oxidation with m-chloroperbenzoic acid gave nitrone 700, which was then hydrogenated in an acetic acid-HCl mixture over Adams catalyst and acetylated in situ to give 701 and 702 isolated by chromatography [92JCR(S)402]. 

In the past, retinyl acetate has been prepared from labeled retinoic acid by the following procedure. Esterification of crystallized al -trans-Tciinoic acid with diazomethane and subsequent reduction of the methyl all-fraw -retinoate with lithium aluminum hydride at low temperature yielded M-trans-rctinol, which was acetylated in situ with acetyl chloride and pyridine in ether to give M-trans-retinyl acetate. 

Especially sensitive quinones can be generated in situ, the diene adduct, eg (88), can be obtained in excellent yield (87). For R = methoxycarbonyl, carboxaldehyde, and acetyl, the yields are 95, 97, and 100%, respectively. 

When nitration of pyridazine iV-oxides is carried out with acyl nitrates (prepared in situ from acyl chlorides and silver nitrate) the reaction takes place at the /3-position relative to the iV-oxide group. Under these circumstances only mononitro derivatives are formed. For example, nitration of pyridazine 1-oxide with acetyl nitrate yields 3-nitropyridazine 1-oxide (17%) and 5-nitropyridazine 1-oxide (0.8%), whereas with benzoyl nitrate a better yield of 5-nitropyridazine 1-oxide is obtained. 

Fig 33 Differentiation of primary (citronellol), secondary (menthol) and tertiary alcohols (linalool) by in situ prechromatographic acetylation citronellol reacts completely, menthol partially and linalool not at all. 

In the one application reported for the conversion of the 17jff-acetyl side-chain to the 17-ketone, the intermediate oxime was not isolated, but hydrolyzed in situ with acid in an overall yield of about 20 %. In the case of 17jff-acetyl-D-norandrostanes, which are particularly difficult to degrade to D-norandrostanes, the nitrite procedure proved the most convenient method. The yield is 25 %, nowhere near the much higher yield obtained by a Baeyer-Villiger reaction which, however, must be allowed to proceed for one month at 0°. ... 

The Barton-Zard (BZ) pyrrole synthesis is similar both to the van Leusen pyrrole synthesis that uses Michael acceptors and TosMlC (Section 6.7) and the Montforts pyrrole synthesis using a,P-unsaturated sulfones and alkyl a-isocyanoacetates." An alternative to the use of the reactive nitroalkenes 1 is their in situ generation from P-acetoxy nitroalkanes, which are readily prepared via the Henry reaction between an aldehyde and a nitroalkane followed by acetylation. Examples are shown later. 

Reaction of 3-(4-methylphenylamino)-4-(4-methylphenylimino)-4//-pyr-ido[l,2-a]pyrazine (373, R = 4-MePh) with ketenes 393, prepared in situ from the appropriate acetyl chloride with NEt3, yielded tricyclic derivatives... 

The rearrangement of dimethyl 5-hydroxy-l-bcnzothiepin-3,4-dicarboxylate (9, R = OH), the first example of a thermal rearrangement of a thiepin derivative without loss of sulfur,12 is analogous to the oxepin-benzene oxide-phenol rearrangement (cf. Section D,l. Introduction and Section 1.2.5.1). This process is catalyzed by the acidic hydroxy substituent. In fact, if this functional group is modified by an in situ acetylation (R = OAc), the usual loss of sulfur occurs. 

Dibenz[c 1c ]azepine (32 a) is obtained by acid-mediated cyclization of 2 -(aminomethyl)bi-phenyl-2-carbaldehyde (31 a), which is generated in situ by reduction of the oxime acetal 30a.85 The acetyl 30 a and benzoyl 30c oximes behave similarly and give the dimethyl and diphenyl derivative 32 b and 32 c, respectively. 

Treatment, in situ, of the unstable 7V-acetyl-2,2 -bis(bromomethyl)diphenylamine (36b) with an excess of phenyllithium yields mainly 5-acetyl-10,l l-dihydro-5//-dibenz[6,/]azepine... 

The syn addition of pentafluoroethyl hypofluorite (CF3CF2OF), generated in situ by the action of anhydrous, hydrogen-fluoride-free fluorine gas on sodium trifluoroacetate, to 5-acetyl-5//-dibenz[/i,/]azepine (11) has been reported to yield 12.135... 

The main application of the enzymatic hydrolysis of the amide bond is the en-antioselective synthesis of amino acids [4,97]. Acylases (EC 3.5.1.n) catalyze the hydrolysis of the N-acyl groups of a broad range of amino acid derivatives. They accept several acyl groups (acetyl, chloroacetyl, formyl, and carbamoyl) but they require a free a-carboxyl group. In general, acylases are selective for i-amino acids, but d-selective acylase have been reported. The kinetic resolution of amino acids by acylase-catalyzed hydrolysis is a well-established process [4]. The in situ racemization of the substrate in the presence of a racemase converts the process into a DKR. Alternatively, the remaining enantiomer of the N-acyl amino acid can be isolated and racemized via the formation of an oxazolone, as shown in Figure 6.34. 

Triazoline imino sugar derivatives 297 that are prospective glycosidase inhibitors have been prepared as single diastereomers in high yield via an lAOC reaction of in situ generated azido alkene 296 (Eq. 32) [78]. m-CPBA oxidation of the dithioacetal groups in the 0-acetylated 5-azido-5-deoxydibenzyl dithio-acetal of o-xylose or D-ribose 294 to the bis-sulfone 295, followed by loss of HOAc between C-1 and C-2 provided the lAOC precursor 296. 

When a reverse procedure was applied, i.e. enzymatic acetylation of racemic 3, formed in situ from the appropriate aldehydes and thiols, the reaction proceeded under the conditions of dynamic kinetic resolution and gave enantiomerically enriched acetates 2 with 65-90% yields and with ees up to 95% (Equation 2). It must be mentioned that the addition of silica proved crucial, as in its absence no racemization of the initially formed substrates 3 occurred and the reaction stopped at the 50% conversion. 

The present work reports the purification and characterization of acetyl esterase from orange fruit as well as the in situ localization of the enzyme by immuno histology. 

The ability of enzymes to achieve the selective esterification of one enantiomer of an alcohol over the other has been exploited by coupling this process with the in situ metal-catalysed racemisation of the unreactive enantiomer. Marr and co-workers have used the rhodium and iridium NHC complexes 44 and 45 to racemise the unreacted enantiomer of substrate 7 [17]. In combination with a lipase enzyme (Novozyme 435), excellent enantioselectivities were obtained in the acetylation of alcohol 7 to give the ester product 43 (Scheme 11.11). A related dynamic kinetic resolution has been reported by Corberdn and Peris [18]. hi their chemistry, the aldehyde 46 is readily racemised and the iridium NHC catalyst 35 catalyses the reversible reduction of aldehyde 46 to give an alcohol which is acylated by an enzyme to give the ester 47 in reasonable enantiomeric excess. 

Fluorination can be carried out using fluorine diluted with an inert gas. However, great care is necessary to avoid uncontrolled reaction.21 Several other reagents have been devised that are capable of aromatic fluorination.22 Acetyl hypofluorite can be prepared in situ from fluorine and sodium acetate.23 This reagent effects fluorination... 

An alternative method, as long as acetylation is not a concern elsewhere in the molecule, is to produce free-phenolic 7-acetates Pl-Ac (Fig. 12.4a, lower scheme). The quinone methides QM1 or QMl-Ac can then be generated in situ by treatment... 

Finally, bisindolylethylenes have also been reacted with tetrahaloph-thalic anhydrides to yield color formers showing absorption in the near infrared.99 The chief advantage over the diarylethylenes is the availability of the starting materials. The bisindolylethylenes may be prepared in situ by reaction of an indole with acetyl chloride and then converted directly to the phthalide without isolation. 

Clerici and Porta reported that phenyl, acetyl and methyl radicals add to the Ca atom of the iminium ion, PhN+Me=CHMe, formed in situ by the titanium-catalyzed condensation of /V-methylanilinc with acetaldehyde to give PhNMeCHMePh, PhNMeCHMeAc, and PhNMeCHMe2 in 80% overall yield.83 Recently, Miyabe and co-workers studied the addition of various alkyl radicals to imine derivatives. Alkyl radicals generated from alkyl iodide and triethylborane were added to imine derivatives such as oxime ethers, hydrazones, and nitrones in an aqueous medium.84 The reaction also proceeds on solid support.85 A-sulfonylimines are also effective under such reaction conditions.86 Indium is also effective as the mediator (Eq. 11.49).87 A tandem radical addition-cyclization reaction of oxime ether and hydrazone was also developed (Eq. 11.50).88 Li and co-workers reported the synthesis of a-amino acid derivatives and amines via the addition of simple alkyl halides to imines and enamides mediated by zinc in water (Eq. 11.51).89 The zinc-mediated radical reaction of the hydrazone bearing a chiral camphorsultam provided the corresponding alkylated products with good diastereoselectivities that can be converted into enantiomerically pure a-amino acids (Eq. 11.52).90... 

A neat synthesis of 4-nitroindole depends on an acylation-deacylation sequence from 2-methyl-3-nitroaniline, as shown in Eq. 10.53.70 On the other hand, treatment of /V-protected indoles with acetyl nitrate generated in situ at low temperature gives the corresponding... 

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