Acylating reagents regioselective

Acylbenzotriazoles 162 are efficient C-acylation reagents for the regioselective conversion of ketone enolates into P-diketones . Diethyl(l-benzotriazolmethyl)phosphinate (163) was found to be a convenient reagent for the stereoselective preparation of (E)-l-(l-alkenyl)benzotriazoles <00SC1413>. The novel three-carbon synthon 1-(1//-133-... 

The 2(3/T)-oxazolone homopolymer 217 and the 2(37f)-oxazolone copolymer 219 with a carbon-carbon bond backbone structure are readily obtained by heating a 3-acyl-2(3/7)-oxazolone alone or with styrene, respectively, at 70 °C in the presence of BPO with the exclusion of air." " ° The A -acetyl polymers serve as regioselective and chemoselective acylating reagents for amines and alcohols (Fig. 5.53). ° ... 

Regiocontrol in these useful reactions is achieved by a careful selection of alkylation or acylation reagent, base, nucleophile, solvent, and reaction temperature. Reactions of oxyazolium salts are useful for regioselective introduction of substituents both at ring positions and at lateral positions. The alkylation or acylation followed by reaction with nucleophile, base, or... 

Aminophenols can be selectively esterified by deprotonation of the hydroxyl group followed by treatment with an acylating reagent of low reactivity (Scheme 7.17). Treatment with a strong acylating agent under acidic conditions will also result in clean esterification. In the presence of weak bases the regioselectivity of the acyla-... 

Tang, Q., Sen, S. E. (1998). Carbomethoxy-propionyl cyanide a regioselective C-acylation reagent for the preperation of P-dicarbonyl compounds. Tetrahedron Lett. 39, 2249-2252. 

An extension of this tin chemistry to the regioselective acylation of unprotected sugars bound to a resin shows the possibility of using solid-phase techniques for the preparation of 0-acyl derivatives of carbohydrates [231]. Very recently, it has been reported that organotin-mediated multiple carbohydrate esterifications can be controlled by the acylating reagent and the solvent polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas when acetic anhydride is employed, kinetic control takes place (O Scheme 31) [232]. 

This reaction was first reported by Nencki et al. in 1881. It is the preparation of an acyl phenol derivative by zinc chloride-activated acylation between a phenol and an acyl chloride, anhydride, or even a carboxylic acid. Therefore, this reaction is generally known as the Nencki reaction. The Nencki reaction generally takes place with at least one equivalent of zinc chloride however, it does not involve the formation of a complex between zinc chloride and acyl chloride or anhydride in a manner similar to that of aluminum chloride. It has been found that the regioselectivity in preference of para-acylation decreases when the size of the acylating reagent increases." ... 

The reaction of an enolate with an acylating reagent often leads to the formation of a mixture of O- and C-acylated products 4]. Therefore, a large amount of work has been undertaken to explore and understand the reaction conditions that promote the regioselective acylation of enolates [5,6]. Microflow reactors have also been used for selective O- and C-acylation. The reaction of the silyl enol ether of acetophenone with benzoyl fluoride using a microflow reactor under EOF conditions selectively gives the... 

The direct regioselective C-acylation of phenol and naphthol derivatives was carried out by using carboxylic acids as acylating reagents. The reactions proceeded smoothly in the presence of a catalytic amount of Hf(OTf)4 to afford the corresponding aromatic ketones in good yields (eq 23). ... 

In addition to the high levels of asymmetric induction, two other attractive features of this sequence of reactions warrant comment. First, both acylation and hydrolysis of the chiral auxiliary are facile, high yield reactions. Second, we have recently found that the lithium hydroperoxide hydrolysis protocol described in Part C is the method of choice for the deaoylation process. This reagent exhibits remarkable regioselectivity for attack at the desired exocyclic acyl carbonyl moiety. ... 

The parent 2(3/i/)-oxazolone moiety functions as a bifunctional leaving group when carboxyl groups are activated for acylations and condensations, similar to other five- and six-membered heterocycles such as imidazole, triazole, and 2-pyridinethiol. The excellent leaving ability of a 2(3//)-oxazolone moiety has led to the development of versatile reagents. Thus, 3-acyl- and 3-alkoxycarbonyl-2(3//)-oxazolones serve as ready-to-use -type agents for the regioselective and chemoselective N-protection of amino alcohols, amino phenols and polyamines. 

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