Heterocyclic 1,2-diacyl

These authors have prepared quite a variety of crown-related esters and have incorporated numerous heterocyclic subunits in the macrorings. The structural variety can be gleaned from a perusal of the tables at the end of this chapter. Despite this variety, one basic approach has been utilized in most of the syntheses thus far presented. This method involves simultaneous addition of separate benzene solutions of the diacyl halide and diol to an additional several volumes of benzene heated at 45—60°. After the ad-... 

The decomposition of diacyl peroxides provides a fairly clean method for the production of alkyl radicals and, therefore, it has been used in most quantitative and preparative studies of the alkylation of heterocyclic compounds,... 

Goldschmidt and Beer have examined the products formed during the thermal decomposition of diacyl peroxides of the type [COgMe —(CHziw—CHz—COO] 2, where n = 1 and 3, in the presence of a series of organic compounds including pyridine and acridine. The products and yields of the reaction with some aromatic and heterocyclic compounds are shown in Table VI. As expected, acridine and... 

Hydrazides (RCONHNH2) are highly useful starting materials and intermediates in the synthesis of heterocyclic molecules.2 They can be synthesized by hydrazinolysis of amides, esters and thioesters.3 The reaction of hydrazine with acyl chlorides or anhydrides is also well known,4 but it is complicated by the formation of 1,2-diacylhydrazines, and often requires the use of anhydrous hydrazine which presents a high thermal hazard. Diacylation products predominate when hydrazine reacts with low molecular weight aliphatic acyl chlorides, which makes the reaction impractical for preparatory purposes.5... 

Tatsuzawa, F. et al., Diacylated malvidin 3-rutinoside-5-glucosides from the flowers of Petunia guarapuavensis. Heterocycles, 45, 1197, 1997. 

Acyl peroxides of structure (16) are known as diacyl peroxides. In this structure R1 and R2 are the same or different and can be alkyl, aryl, heterocyclic, imino, amino, or fluoro. Acyl peroxides of structures (17), (18), (19), and (20) are known as dialkyl peroxydicarbonates, OO-acyl ((-alkyl monopcroxycarbonatcs. acyl organosulfonyl peroxides, and di(oiganosulfonyl) peroxides, respectively. R1 and R2 in diesc structures are the same or different and generally are alkyl and aryl. Many diacyl peroxides (16) and dialkyl peroxydicarbonates (17) are produced commercially and used in large volumes. 

A similar unravelling of the heterocyclic ring occurred in intramolecular reactions with furans,79b,159 161 leading to cyclic 1,4-diacyl-1,3-butadienes (204 equation 42)159 and (205 equation 43).79b The ideal size for the tether was five, but less efficient capture of the carbenoid was also possible with six- and seven-membered rings. With the 3-furanyl derivative (206), the acid labile structure (207) was formed, which readily rearranged to p-hydroxyphenylacetaldehyde (208 Scheme 43).161... 

However, acylation reactions of N-unsubstituted pyrazolines with halogen anhydrides of acids are very often followed by the destruction of the heterocyclic ring owing to the ease of breaking the C(5)—Nq) bond located at the (3-position of the azomethine group [140, 141, 142, 166]. For example, pyrazoline 108 treated with halogen anhydrides of acids yields a,(3-unsaturated ketone 109 and diacyl-hydrazine 110 [166] (Scheme 2.29). 

The reaction of l-aryl-3,4-diacyl-4-(2-furyl)butan-l-ones with acid or with phosphorus pen-tasulfide led to [2, -b 3,4-c ]benzodifurans and thieno[l,2-c 3,4-//]benzofurans, by simultaneous cyclization of heterocyclic and carbocyclic rings <74BSF2105>. 

The SjSii ring system is susceptible to attack by nucleophiles, as is illustrated for 636. Examples of nucleophiles are alcohols (best with primary and secondary), 1563-1538 phenols,hydroxide ion, water, " and carboxylic acids. The boron compound 641 reacts with 636 to give the five-membered heterocycle 642. The electrophilic reagents, acetyl chloride and benzoyl chloride, react with tetraphenylcyclodisiladithianes to give the diacyl sulfide and dichlorophenyl-silane. ... 

When the decomposition is carried out in an inert solvent, methyl acetate and ethane are formed, whereas in the gas-phase decomposition methyl acetate is completely absent and ethane is produced in much smaller quantity.85 It was suggested that the dimers in solution represent the recombination of methyl, and the combination of methyl and acetoxy radicals, within the solvent cage. 85 87 The decomposition of diacyl peroxides provides a fairly clean method for the production of alkyl radicals and, therefore, it has been used in most quantitative and preparative studies of the alkylation of heterocyclic compounds. 

The introduction of an acyl group activates the heteroaromatic ring towards further acylation, which however always takes place exclusively at the positions X and y to the heterocyclic nitrogen (the protonated nitrogen is by far the main activating factor, which determines the positional selectivity). Thus, if a heterocyclic compound has two reactive positions, it is easy to obtain diacyl derivatives, but only one isomer (for example 2,4-diacylderivatives in the case of quinoline), whereas the monoacylderivatives prevail only at very low conversions. Due to the nucleophilic character of alkyl and acyl radicals, the behavior of homolytic... 

The foregoing transacylation method was later employed in the synthesis of other highly bioactive cephamycin derivatives including CS1170 (Nakao et al., 1976 Shimizu et al., 1976). N-BOC-protected esters (425) were diacylated (426) with chloroacetyl chloride (or faster with bromo-acetyl bromide) and bis(trimethylsilyl)trifluoroacetamide in methylene chloride (40°C). Trifluoroacetic acid treatment afforded the transacylated acid (427). Nucleophilic substitution of 427 by a variety of heterocyclic mercapto compounds in the presence of 2 equiv of sodium hydroxide gave a series of semisynthetic cephamycins for which antibacterial data were given vide infra). 

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