Benzoylation s. Acylation

Benzoxazolones, N-aniino-methylation 17, 407 Benzoylacetone s. Sodium/ benzbylacetone Benzoylation s. Acylation Benzoyl chloride as reagent 16, 609, 819, 970 Benzoyl peroxide as reagent 16, 369, 578 17, 311, 655, 897 Benzylamines, sec. 

Benzoxazolones, N-amino-methylation 17, 407 Benzoylacetone s. Sodium/ benzoylacetone Benzoylation s. Acylation Benzoyl chloride as reagent... 

Acylation of pyridazinethiones with acetyl chloride or benzoyl chloride gives the corresponding S-acylated products. 6-Mercaptopyridazine-3(2//)-thione gives either mono- or di-S-acylated products. A bispyridazinyl derivative is formed when phosgene or thiophos-gene is used as acylating agent. 

Other indirect diazo transfer routes to a-diazo ketones have been reported involving initial activation of the ketone by benzoylation and acylation with diethyl oxalate (a) Metcalf, B. W. Jund, K. Burkhart, J. P. Tetrahedron Lett. 1980, 21. 15 (b) Harmon, R. E. Sood, V. K. Gupta, S. K. Synthesis 1974, 577. 

A potential problem in the coupling of S-acyl or S-alkoxy-carbonyl-L-cysteine derivatives to other -blocked amino acids is S - iV-acyl migration which results from the presence of the free amino group on the S-acyl cysteine residue. The mechanism for S - -N-dicy m ation has been disj ussed by Barnett and Jenks [145]. Patchornik et al. [8] noted that S- iV-acyl miration occurred when the free base of (60) was prepared and the low yields of S-benzoyl-L-cysteine peptides such as (61) were traced to the formation of (62), produced by S- -N-benzoyl migration during the coupling step [89, 146]. Similar difficulties have been noted in solid-phase synthesis [120]. Problems of this type may have also been encountered in the... 

Two disadvantages are associated with the use of S-acetyl or 5-benzoyl derivatives in peptide syntheses (a) base-catalyzed hydrolysis of 5-acetyl- and 5-benzoylcys-teine occurs with /S-elimination to give olefinic side products, CH2=C-(NHPG)CO—(b) the yields of peptides formed by coupling an unprotected amino group in an 5-acylcysteine are low because of prior S-N acyl migration. ... 

The same is true for decarbonylation of acyl radicals. The rates of decarbonylation have been measured over a very wide range of structural types. There is a very strong dependence of the rate on the stability of the radical that results from decarbonylation. For example, rates for decarbonylations giving tertiary benzylic radicals are on the order of 10 s whereas the benzoyl radical decarbonylates to phenyl radical with a rate on the order of 1 s . ... 

When it s necessary to refer to the R-C=0 as a substituent, the name acyl (a-sil) group is used and the name ending -yl is attached. Thus, CFI3CO is an acetyl group, CHO is a formyl group, and C6H5CO is a benzoyl group. 

These amino acids were initially synthesized by asymmetric aminomethylation of optically pure (R)- and (S)-N-Acyl-4-phenyhnethyl)oxazolidin-2-ones 52 through TiCVenolates (Evans methodology [135]) with (benzoylamino)methylchloride or benzyl N-(methoxymethyl)carbamate [66, 97-99, 104]. Hydrolytic removal of the auxiliary yielded the N-protected (benzoyl or Z) amino acid 54. Deprotection afforded the free amino acid which was converted to the required Boc- or Fmoc-pro-tected derivatives (Scheme 2.7). 

In 1967, (3) it was discovered that DMAP catalyzes the benzoylation of m-chloroaniline 10 times faster than pyridine. This enormous increase in reaction rate is unmatched by any other nucleophilic acylation catalyst (3. It was shown that the catalytic action of DMAP and PPY is not primarily due to their larger pKa s with respect to pyridine, but is a result of enhanced nucleophilic catalysis. 

The benzoyl derivative, PhCOMn(CO)5 and related acyl derivatives have intrinsic interest because they can be prepared by alkyl group migration to coordinated CO, a formal internal nucleophilic attack. This reaction, which is often referred to as carbonyl insertion86), is reversible in certain instances to give the metal alkyl. The enthalpy of disruption for PhCOMn(CO)s (Table 13) can be divided up to give the b.e.c of the Mn-COPh bond if the values of T (Mn-CO) shown in Table 13 are used, then the Mn-COPh enthalpy lies in the range 105 10 kJ mol-1, the lower value being preferred as outlined earlier. 

The conversion of biguanides into guanamines under the influence of acylating agents is well known (see also Section VII 12). Acetic anhydride or benzoyl chloride in conjunction with alkali react with the parent compound, gelding 2-methyl- 519) or 2-phenyl-4,6-diamino-s-triazine 17) (LXXXI R = Me or Ph) respectively. 

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