Electrophilic acetylation

This structure determination affirms the spectroscopic indication that the product of the reaction of Cp2Zr[C(0)Me]Me and Cp2ReH involves geminal addition of the Re-H bond to the electrophilic acetyl carbon. 

Partly hydrogenated systems are less stable than the fully unsaturated derivatives. Compound (160) was found to dimerize more easily than its unsaturated counterpart (156). The partly reduced ether (161) is sensitive to electrophilic acetylation on nitrogen and is hydrolyzed by hot water to give 2-(2-aminophenyl)ethaneboronic acid. Compound (115), on the contrary, is not acetylated and is recovered from boiling concentrated hydrochloric acid and boiling 40% potassium hydroxide. Also, compounds (22) and (162) (see Scheme 24) show very different behaviour towards air, water and acids, (22) being the more stable. 

Which reagent is best can often only be determined by experimentation—commercially, paracetamol is made from para-aminophenol and acetic anhydride largely because the by-product, acetic acid, is easier to handle than HC1. In a retrosynthetic analysis, we don t really want to be bothered by this sort of decision, which is best made later, so it s useful to have a single way of representing the key attributes of alternative reagents. We can depict both anhydride and acyl chloride in this scheme as an idealized reagent —an electrophilic acetyl group MeCO+. 

Phenols add intramolecularly to Michael acceptors. " Under acidic conditions, a one-pot sequence starts with initial electrophilic acetylation of the activated aromatic ring and is followed by cyclization." With an appropriate leaving group in the /f-position (OMe. or other amines such as in the unsaturated carbonyl compound (e.g., 4) is formed. Other approaches to pyroncs include the self-condensation of protected //-hydroxy acrylates,intramolecular aldol reactions followed by condensation,thermal cycli-zations of unsaturated ()-chloro esters,and an iodo-cyclization-elimination sequence w th Michael acceptors.Oxymercuration of an unsaturated alcohol is an alternative cyclization approach to tetrahydropyrans. 

Dihydroxyacetophenones 20 are synthesized with satisfactory yield through a multistep process (Scheme 2.10)2 i Compounds 19 carrying an alkyl chain between the two methoxy groups are synthesized by the well-known method based on the selective deprotonation of 18 at the C-2 positions The electrophilic acetylation of compounds 19 can be performed under mild conditions with acetic acid in the presence of hydrobromic acid... 

BEA zeolites show good activity also in the electrophilic acetylation of naphthalene with AAISP and BC. The BEA(75) zeolite with channel diameter 7.6 x 6.4 A exhibits the highest activity in naphthalene acetylation with AAN (24% naphthalene conversion) (Scheme 4.14) in comparison with Y(6) with channel diameter 7.4 A (3% naphthalene conversion), and MOR(20) with channel diameter 6.7 x 7.0 A (3% naphthalene conversion). Reactions are performed at 137°C for 2.5 h. Despite the significant differences in naphfhalene conversion observed for MOR(20) and BEA(75), practically fhe same selectivity to 1- and 2-acetylnaphthalene is observed (about 25% and 75%, respectively). In contrast, a lower selectivity to 2-acetylnaphthalene is observed for Y(6), which possesses large cavities in its structure that enable the formation of 1-isomer. 

The regioselectivity of electrophilic addition to the 3-oxaplatina(II)cyclo-butane complex (89) is very dependent on the nature of the electrophile. Treatment of (89) with the strong electrophile acetyl chloride leads to exclusive attack at the hard metallacycle oxygen [Eq. (29)], to give the ring-opened product... 

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