Selective acetylations acetyl chloride

Dependence of apparent constants on concentration. We continue the consideration of Scheme XXIII by making chemically reasonable tentative selections of the forms of A a and k[. First, consider the acetyl chloride-alcohol reaction. Because the spectral observations show that intermediate formation is essentially complete, this system belongs to the case in which kdk i may be treated as infinite (Scheme XXIV). The observed reaction is then... 

For the acylation of naphthalene, the ionic liquid gives the highest reported selectivity for the 1-position [95]. The acetylation of anthracene at 0 °C was found to be a reversible reaction. The initial product of the reaction between acetyl chloride (1.1 equivalents) and anthracene is 9-acetylanthracene, formed in 70 % yield in less than 5 minutes. The 9-acetylanthracene was then found to undergo diacetylation reactions, giving the 1,5- and 1,8-diacetylanthracenes and anthracene after 24 hours (Scheme 5.1-64). 

Whereas treatment of ( )-29 with camphanic chloride achieves the selective esterification of the hindered C-9 hydroxyl group, the action of acetic anhydride on (+)- 29 results in the equally selective acetylation of the C-10 hydroxyl group It is not clear to what this discrepancy should be attributed, so we will not offer a rationalization here. This unexpected result is, however, most gratifying because TPAP-NMO oxidation27 of the remaining C-9 hydroxyl furnishes keto acetate 6 (88 % overall yield). You will note that the contiguous keto and acetate functions in 6 are both expressed in the natural product. 

Ogawa et al. (1998b) have shown how 1,4-butanediol to 1,16-hexadecanediol and 1,4-cyclohexanediol, adsorbed on silica gel, can be reacted with acetyl chloride to give nearly 100% selectivity for the mono-acyl derivative. The above examples give an indication of the versatility of this strategy in the manufacture of fine chemicals. There are, however, many aspects associated with the role of mass transfer, which have yet to be studied thoroughly. 

Ethoxycarbonyl chloride is, by virtue of resonance involving the ester function, less reactive than acetyl chloride, and the reagent has found application for selective O-acylation in the steroid field.34 With this reagent, methyl 4,6-O-benzylidene-a-D-glucopyranoside yielded35 2- and 3-esters in the ratio 24 1, and the related benzyl-thiocarbonyl chloride gave the 2-ester in 58% yield.36... 

One example for the reaction of a 229-type copper reagent is shown in Equation (128). Neopentyl-substituted organocopper reagent 230, which bears aldehyde, is generated followed by treatment with acetyl chloride to provide coupling product 231 in 70% yield. Application of this method to the selective functionalization of polyhalogenated aromatics was also reported.497... 

It has been demonstrated that organotin-mediated multiple carbohydrate esterifications can be controlled by the acytaring 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. Very good selectivity can furthermore be obtained in more polar solvents. These results can be used in the efficient preparation of prototype carbohydrate structures. 

Use of a large, lipophilic nitrogenous component results in a 1idocaine like, local anesthetic type cardiac anti-arrhythmic drug, lorcainide (20). Synthesis begins with the Schiff s base (1 ) derived by reaction of p-chloro-aniline and borohydride followed by acylation with phenyl acetyl chloride produces amide 1 . Selective hydrolysis with HBr followed by alkylation with isopropyl bromide completes the synthesis of lorcainide (20). ... 

The association between acetylcholine levels and Alzheimer s disease, as noted more than once previously, has led to the search for novel compounds that raise the level of that neurotransmitter by inhibiting acetylcholinesterase, the agent of its inactivation. The benzisoxazole icopezil (60-8) has undergone several trials against that debilitating disease as a result of selective chohnesterase inhibiting activity in the CNS. Friedel-Crafts acylation of the indolone (60-1) with acetyl chloride affords the methyl ketone (60-2). This is then converted to its oxime and that function acylated with acetic anhydride to yield (60-3). Treatment with pyridinium perbromide... 

Acyl chlorides were also tested in acylations promoted by B(OTf)3.231 Acylation of benzene and toluene in competitive reactions (molar ratio = 5 1) with acetyl chloride shows high para selectivity (92-95% with 2.5-7% of meta, kT/kB — 31-73), whereas the para isomer is formed only with 72-75% selectivity (8-10% of meta, k lkK = 78) in benzoylation with benzoyl chloride. Acetylation appears not to be affected by significant isomerization as indicated by isomer distributions and relative reactivity data. 

It is possible to achieve selective esterification at OH-6 in good yield even with acetyl chloride by employing low temperature in the presence of a controlled amount of acylating agent.13,93 Some tin derivatives (such as dibutyltin oxide) also show significant selectivity towards position 6 (Scheme 7).94,95 A polymer-bound stannyl reagent was also applied for the selective C-6 acetylation of... 

M 54] [P 48] The ability of the separation-layer concept to prevent fouling even under severe conditions was demonstrated for two fast precipitating reactions, bisquaternization of 4,4 -bipyridyl and amide formation from acetyl chloride [39], Stable operation for a few hours, and in selected cases longer, was achieved. 

Pyridones may be selectively acylated at oxygen by treatment with acetyl chloride in acetone in the presence of potassium carbonate <2001JOC3646>. 2-Pyridones are also selectively O-acylated with 2-bromobenzoyl chlorides in high yield using potassium carbonate and tetrabutylammonium bromide (TBAB) in acetone <2003T3009>. For example 3-methoxy-2(17/)-pyridone is acylated in 88% yield by 2-bromobenzoyl chloride under these conditions (Equation 73). 

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