P acylation

Less reactive electrophilic reagents like those involved in acylation or alkylation apparently do not react with phenyl-substituted pyrylium salts the p-acylation of a phenyl group in position 3 of the pyrylium salt obtained on diacylation of allylbenzene (Section II, I), 3, a), and the p-l-butylation of phenyl groups in y-positions of pyrylium salts prepared by dehydrogenation of 1,5-diones by means of butyl cations (Section II, B, 2, f) probably occur in stages preceding the pyrylium ring closure. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

Parsek, M.R., Val, D.L., Hanzelka, B.L., Cronan, J.E. Jr., Greenberg E.P. Acyl homoserine-lactone quorumsensing signal generation. Proc Natl Acad Sci USA. 1999 13 4360-4365. 

The 1-methylpyrrole complex 21 undergoes clean acylation at the P-position in the presence of Ac20/DMAP to give the 3-acetyl-1-methylpyrrole complex, 38 (Figure 10).12b Propionic anhydride reacts with 21 in a similar manner to form 39. Under these reaction conditions, the parent pyrrole complex (20) undergoes exclusive A-acylation to give 40, and the 2,5-dimethylpyrrole complex (22) gives a 7 3 ratio of N- to P-acylation. 

Recently, Boeckman and Pruitt [58] demonstrated the use of dioxolenones as precursors of P-acyl ketenes, which can be thermally generated under mild neutral conditions in the absence of other nucleophiles and trapped intramolecularly by the hydroxy group to afford good yields of macrocyclic lactones. The 16-membered macrolide (—)-kromycin 102) has been synthesized in this way by thermolysis of the P-acyl ketene precursor 101 in toluene at high dilution (0.0001 M) in 70% yield (Scheme 34). 

B) - The enzymatic hydrolysis of P-acyls of dilinoleoylphosphatidilcholine (DLPC) in the liposomal membrane by phospholipase A from Apis melifera venom (1), hydrolysis rate of unoxidized DLPC liposomes (2), hydrolysis rate of DLPC liposomes which preliminarv was oxidized by C-l rabbit... 

Corbel, B., L Hoslis-Kcrvclla, I., and Haelters, J.-P, Acylation of diethyl phosphonoacetic acid via the MgClj/EtjN system. A practical synthesis of P-keto phosphonates. Synth. Commun., 30, 609. 2000. Kim, D.Y., and Suh, K.H., Solid phase acylation of phosphonoacetates. Synthesis of P-keto phosphonates from polymer bound phosphonoacetate, Synth. Commun.. 29. 1271, 1999. 

Vilsmeier acylation of pyrroles, formylation with dimethylformamide/phosphoryl chloride in particnlar, is a generally applicable process. The actual electrophilic species is an Al,Al-diaIkyl-chloromethyleneiminium cation (the chloride is available commercially as a solid). " Here again, the presence of a large pyrrole-A-substituent perturbs the intrinsic a-selectivity, formylation of A-tritylpyrrole favonring the P-position by 2.8 1 and trifluoroacetylation of this pyrrole giving only the 3-ketone " the nse of bulky iV-silyl substituents allows P-acylation with the possibility of subsequent removal of the N-snbstituent." The final intermediate in a Vilsmeier reaction is an iminium salt requiring hydrolysis to prodnce the isolated product aldehyde. When a secondary lactam is used, hydrolysis does not take place and a cyclic imine is obtained." ... 

Fig. 4. Ether phospholipid synthesis from dihydroxyacetone-phosphate. (A) Dihydroxyacetone-P acyl transferase (DHAPAT). The first step of ether phospholipid synthesis is catalyzed by peroxisomal DHAPAT. This enzyme is a required component of complex ether lipid biosynthesis and its role cannot be assumed by a cytosolic enzyme that also forms acyldihydroxyacetone-P. (B) Ether bond formation by alkyl-DHAP synthase. The reaction that forms the 0-alkyl bond is catalyzed by alkyl-DHAP synthase and is thought to proceed via a ping-pong mechanism. Upon binding of acyl-DHAP to the enzyme alkyl-DHAP synthase, the pro-f hydrogen at carbon atom 1 is exchanged by enolization of the ketone, followed by release of the acyl moiety to form an activated enzyme-DHAP complex. The carbon atom at the 1-position of DHAP in the enzyme complex is thought to carry a positive charge that may be stabilized by an essential sulfhydryl group of the enzyme thus, the incoming alkox-ide ion reacts with carbon atom 1 to form the ether bond of alkyl-DHAP. It has been proposed that a nucleophilic cofactor at the active site covalently binds the DHAP portion of the substrate.

Some 1,2-dihydroisoquinoline-l-ylphosphonates, e.g. (18), have been prepared from trialkyl phosphites, isoquinoline, and a sulfonyl chloride. Quinoline gave similarly the corresponding l,2-dihydroquinoline-2-ylphosphonates. The superbase (19) has been shown to be a very effective catalyst for the acylation of hindered and/or acid-sensitive alcohols with benzoic anhydride a P-acylated intermediate (20) was inferred from NMR data. 

The enhanced acidity conferred upon p-acyl phenols is sufficient for their participation in Mitsunobu displacements. Scheme 4.171 shows an example in which selective O-benzylation of the p-hydroxyl in the orcinol derivative 171.1 took place in preference to the o-hydroxyl. ... 

The finding of plants with high proportions of molecular species with 16 carbon fatty acids at both sn-1 and sn-2 positions requires a revision of our conclusions regarding the fatty acid specificity of the G-3-P acyl-ACP transacylase. We... 

The reaction of diaz (26) with Fe2(CO)g yields [(diaz)Fe2(CO)g] which contains no N—N bond and two non-equivalent iron atoms. Spectral studies and an X-ray crystallographic determination have also been reported, [(diaz H2)Fe2(CO)g] [diaz H2 = (27)] has also been isolated and spectroscopic studies of this compound indicate that it possesses a similar structure to [(diaz)Fc2(CO)g], but with somewhat greater distortions at one of the octahedral iron atoms. Reactions of phthalazine with iron carbonyls have also been studied and are outlined in Scheme 2. The p-acyl compounds [Fc2(CO)g-(p-COR)2] react with donor ligands (L) to form [Fe2(CO)5L(p-COR)2] (R = Me or Ph L = NH3, Et2NH, PhNHNHj, py, or CsH,oNH) and with thiols and selenols to form [Fe(CO)3(p-X)]2 (X = SEt or SePh) and the aldehydes PhCHO and MeCHO. Reaction of [Fe2(CO)g(p-COPh)2] with three molar equivalents of PR3 gives (28), Fe(CO)3(PR3)2 (R = Ph or Pr ), and carbon monoxide. The structure of (29) has been determined. ... 

Depending on the substituents and R, reactions of the 1,3,5-triphosphinines 11 with the nitrile oxide 58 in ether or toluene lead either to the trisadducts 59 or proceed with ring contraction from a six- to a five-membered ring to afford the bisadducts 60 with a P-acyl substituent [54]. 

See Ethyl cbloroacetoaoetate. ca-Chloro-l>acetonaphibcme (u-No/p acyl chloride, chloromethyl ketone, l-Moro-... 

Phosphoryl hydrazides, P-acyl-amino-P-aziridinyl-N -tosyl-... 

Trimethylsilyl azide j stannic chloride I stannous triflatej lithium perchlorate a-Glycosyl azides from P-acyl glycosides s. 44, 206 OAc... 

P-Chlorvinylketone 11 reagieren mit Triphenylphosphin glatt zu P-Acyl-vinylphosphoniumsalzen 72, deren Reaktionen studiert wur-den 1 ). 

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