Miscellaneous acylations

The base, or amino acid mixtures or their hydrochlorides (ca. 1 mg), is dissolved in a small amount of methanol or THF (10-20/il) and is heated with pivalic anhydride (200/il) and triethylamine (10-15) at 70-110 °C for 30 minutes. Alternatively, a mixture of pivalic anhydride, triethylamine and methanol (20 1 1, 250/d) is used. The reaction mixture, if cloudy, is centrifuged and the supernatant is evaporated to dryness in a stream of nitrogen or in vacuo. The product may be taken up in a suitable solvent (hexane, benzene, chloroform etc.) for analysis [135-137]. 

If pivaloyl chloride is used, the amine or its hydrochloride (up to 5 mg) is suspended in chloroform (200 /il) and light magnesium carbonate (50 mg) is added. To the stirred suspension is added a 110% molar excess of pivaloyl chloride via a microlitre syringe, and the reaction is allowed to proceed at room temperature for 30 minutes. After centrifugation, the supernatant is evaporated to dryness in a stream of nitrogen or in vacuo, and the residue is dissolved in a suitable solvent for analysis by TLC or GC [138]. 

The trichloroacetyl derivatives of amines are among the most electron-capturing derivatives [139]. The amine or amine extract (up to 1 mg) is treated with trichloroacetyl cloride (50 /il) in hexane (1 ml) at room temper- 

Benzoyl and benzenesulphonyl derivatives have not been widely applied for chromatographic analyses, but because they can be detected in the ultraviolet they have found some use in HPLC. They are also used to make derivatives from volatile compounds as a means avoiding evaporative losses. They are readily made under Schotten-Baumann conditions. Thus, an amine solution (3 ml) is made alkaline with an equal volume of 7.5 M NaOH, and 50 fi of benzoyl choride is vigorously shaken with this solution until consumed. The product is extracted twice with 2 ml of diisopropyl ether, and the ether extracts are blown dry with nitrogen before being taken up in the ether for analysis [142]. A similar procedure was used for amines by Terashi et at. but using benzenesulphonyl chloride [143]. 

Pyridine has also been used as the basic catalyst and chloride acceptor for benzoylation reactions. In one procedure, amines, volatile alcohols or thiols isolated by benzene extraction, are benzoylated with pyridine (1 ml) and benzoyl chloride (0.5 ml) by shaking intermittently at room temperature for several hours. The pyridine phase is extracted with 2 M HCl and the excess benzoyl chloride is hydrolysed with water for 12 hours. After shaking with 2 M sodium carbonate to remove benzoic acid, the benzene solution is dried and concentrated for analysis [144]. Aminoglycoside antibiotics are derivatized to the benzoyl derivatives in a similar reaction using 90 fi of pyridine and 10 /il of benzoyl chloride at 80 °C for 30 minutes. The pyridine is evaporated in a stream of nitrogen and excess benzoyl chloride is converted to methyl benzoate with methanol, again at 80°C, for 10 minutes. The product is cleaned up for analysis by a rather involved solvent extraction procedure [145]. 

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RCH(NH2)C02H RCH(NHCSNHC(,H5)C02H X(OH) + [(RiC0)20 + (R2C0)20)]-miscellaneous acyl derivatives... 

Miscellaneous. Acylation of unprotected amino acids, desilylation of TBS-ethers, alkylation of ketone enolates with (iso)/quinolinium salts, Wolff rearrangement, bromination of active arenes with NBS, and dichloroketene formation from Zn and CI3CCOCI (for cycloaddition to alkynes) have all been promoted with ultrasound. 

Miscellaneous Reactions. Reactions of potential commercial significance include acylation by ketene [463-51-4]-. 

Sulphonylbenzofurans 638 a-Sulphonyl carbanions 760, 766, 767, 797, 813, 951, 961 acylation of 627-636 addition to unsaturated bonds 636-642 alkylation of 627-636, 781 halogenation of 1058-1060 Michael addition of 642-649 miscellaneous reactions of 653-655 Ramberg-Backlund reaction of 649-653, 1057, 1058... 

MISCELLANEOUS FIVE-MEMBERED HETEROCYCLES Acylation with 3-chloropropionyl chloride of the... 

Methods for the A-acylation of similar heterocycles, such as simple thiazolidinethiones, have been reported since 1977, namely acyl chlorides in miscellaneous conditions,586 or carboxylic acids under DCC-activation.60,61 However the easiest and most effective method involves acyl chlorides or carboxylic anhydrides in the presence of an amine.47 Applying that procedure on carbohydrate scaffolds Rollin and co-workers62 reported the synthesis of diverse /V-acylated OZTs. The reactions were performed with good yields and the /V-selective acylation was ascertained by NMR— namely the thiocarbonyl 13C chemical shift (Scheme 41). Thanks to the dual nature of the carbanion drifting in the reaction,596 60 no competitive formation of the thioester, as mentioned by Plusquellec el al. in the case of benzothiazole, was observed. 

Silylcuprates have been reported to undergo reactions with a number of miscellaneous Michael acceptors [65]. Conjugate addition to 3-carbomethoxy acyl pyri-dinium salts [65a] affords 4-silyl-l,4-dihydropyridines. Oxidation with p-chlorand generates a 4-acyl pyridinium salt that gives the 4-silylnicotinate upon quenching with water, and methyl 4-silyl-2-substituted dihydronicotinates upon quenching with nucleophiles (nucleophilic addition at the 6-position). The stabilized anion formed by conjugate addition to an a, j8-unsaturated sulfone could be trapped intramolecularly by an alkyl chloride [65b]. 

Heterocyclic ring closure of o-hydroxylated or o-acylated styrene, stilbene, and stilbazole derivatives. This group includes miscellaneous methods, the final stage of which involves ring closure of compounds as in Eq. (2). Starting from o-acyloxystilbenes, the reaction provides... 

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