Acylations using

Alkyl, aryl, acyl. Used for colored pliotogra- 1036... 

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

Chiral diene—iron tricarbonyl complexes were acylated using aluminum chloride to give acylated diene—iron complexes with high enantiomeric purity (>96% ee). For example, /ra/ j -piperjdene—iron tricarbonyl reacted with acyl haUdes under Friedel-Crafts conditions to give l-acyl-l,3-pentadiene—iron tricarbonyl complex without any racemization. These complexes can be converted to a variety of enantiomericaHy pure tertiary alcohols (180). 

C-7 Amino Acylation. Essentially all the known methods for amine acylation, used in the peptide field, have been apphed to cephalospotins. 

To synthesize the monoxacetam stmctures (Fig. 6), alkylation of A/-protected 1-hydroxyazetidinones (46) with the appropriate haloacetic acid derivatives provided (47). Alternatively, (47) could be prepared from the acycHc hydroxamate ester (48). Deprotection of (47) furnished the zwitterionic intermediate (49) [90849-16-4] CgH2QN204, which subsequendy underwent acylation using the C-3 aminothiazole oxime side chain to afford SQ 82,291 (45) also known as oximonam (37). 

In the course of synthesizing DNA-gyrase inhibitors Hogberg, Mitscher, and coworkers determined that an effective means of constructing the core of their inhibitors was via a K-R reaction. Under mild conditions, keto ethylester 52 was acylated using acetic formic anhydride in the presence of sodium formate to deliver chromone 53 in 75% yield. 

S)-2 are obtained by N-acylation using diethyl phosphorocyanidate (DEPC) (ref. 5), followed by hydrolysis. The results are summarized as follows. 

This reaction, similar in scope and mechanism to 10-55, can be carried out with ammonia or primary or secondary amines. Amino acids can be N-acylated using... 

An irreversible procedure for the lipase-catalyzed acylation using vinyl esters as acylating agent has been developed, where a leaving group of vinyl alcohol tautomerizes to acetaldehyde. In these cases, the reaction with the vinyl esters proceeds much faster to produce the desired compounds in higher yields, in comparison with the alkyl esters. 

Other acylations using the copolymer l-acyl-4-vinylimidazole/divinylbenzene/ styrene (48 4 48) in solvents like 1,4-dioxane, benzene, diethylether, or acetone produce within reaction times of three hours the amide yields listed in Table 4-4.[122]... 

Figure 1.11 Tyrosine residues are subject to nucleophilic and electrophilic reactions. The unprotonated phe-nolate ion may be alkylated or acylated using a variety of bioconjugate reagents. Its aromatic ring also may undergo electrophilic addition using diazonium chemistry or Mannich condensation, or be halogenated with radioactive isotopes such as 12iI.

Benters et al. (2002) used two approaches to modify APTS surfaces. In one instance, the amine groups were acylated using glutaric anhydride to create carboxylate functionalities, which were then activated with NHS/DCC to form the NHS ester. This derivative could be... 

Scheme 4.6 Friedel-Crafts acylation using a graphimet as sensitizer and catalyst.

TABLE 3-3. Asymmetric Acylation Using (2A,5A)-24 and Subsequent Stereoselective Reduction with Zinc Borohydride in THF at —78°C... 

Block (cap) residual lysine residues with a carboxylic acid by acylation using succinic anhydride prepared in l-methyl-2-pyrrolidinone,... 

In the context of our work in the area of chiral nucleophilic carbenes and their utility in organic synthesis, we have developed a conceptually distinct approach to catalyzed acylation using a-haloaldehydes as acylation precursors. The use of a chiral triazolium salt in the presence of base allows an enantioselective desymme-trization of meio-hydrobenzoin to proceed in 83% ee and good yield ... 

Although diketo- and ketopiperazines can be formed by coupling the Ugi reaction with an intramolecular acylation using convertible isocyanides, as described earlier, the approach that involves Sn2 reactions enables the introduction of an additional substituent R avoiding the loss of the diversity carried by the isocyanide. 

The thermal cyclization of the indol-3-yldienamines 360 (R = H, Ph, or OH), which gave the 4-cyanocarbazoles 361, are presumably driven to completion by the loss of dimethylamine. Intramolecular indole a-acylation using ester acids (362 R = H or Me) produced by Stobbe condensation gave... 

Table 10. Enantioselective Hydrolysis and Acylation Using Lipases...

NPIL). The chiral triol was produced in a whole cell reduction process and was then selectively protected at the primary alcohol by enzymatic acylation using Novozyme 435 (CAL-B). Finally the key intermediate was produced by protecting the two secondary alcohols as they cleanly reacted with dimethoxypropane to give a crystalline product (>99 % ee, >99 % de, 96 % purity) which was subsequently used for Lipitor production (Figure 1.44). 

The enantiopreference of the protease subtilisin in the acylalion of chiral alcohols is known to be opposite to that observed with lipases, providing for access to both enantiomers with DKR, depending on the enzyme used [137, 138, 139]. Acylation using 2,2,2-trifluoroethyl butyrate as the acyl donor was combined with in situ racemization, affording the corresponding esters in high yield and [135]. 

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