4-Methoxybenzoic anhydride

In many cases, the trimethoxybenzoyl group has been introduced into synthetic methyl reserpate as the last or second-to-last step. An optimal yield of 72% of reserpine is reported if a 50% excess of the acid chloride is used (190, 193), the yield diminishing as the amount of acylating agent is increased. In the French synthesis, acylation is carried out with tri-methoxybenzoic anhydride in triethylamine and pyridine (185). 

In order to extend the scope of the reaction, and with the aim of designing a greener approach to the above set of reactions, we preformed the acylation of the same substrates with different acylation agents, such as maleic anhydride, p-methoxybenzoic acid and acetic acid (Scheme 48.4). Table 48.3 shows the results for acylation of benzenesulfonamide. 

Maleic anhydride p-methoxybenzoic acid Acetic acid ... 

To a solution of 4-amino-5-chloro-2-methoxybenzoic acid (20.2 g) in methyl isobutylketone (250 ml) and triethyl amine (15.3 ml) was slowly dropped ethyl chloroformate (9.6 ml). The reaction mixture was stirred for 30 min at room temperature. To the formed mixed anhydride was then added l-[3-(4-fluorophenoxy)-propyl]-3-methoxy-4-piperidinamine (28.2 g) and the reaction mixture was stirred for 2 hours at room temperature. Subsequently, the reaction mixture was washed with water (80 ml) and a NaOH solution (6.5% w/v, 50 ml). The organic layer was warmed to 65°C and methanol (50 ml) and water (8.5 ml) were added. The solution was cooled slowly and stirred for 2 days during which crystallisation occurred, yielding benzamide, 4-amino-5-chloro-N-(l-(3-(4-fluorophenoxy)propyl)-3-methoxy-4-piperidinyl)-2-methoxy-, monohydrate, cis- (Cisapride) having a cis/trans ratio higher than 99/1. 

Acetic anhydride added to a suspension of 2,3-dihydro-8-methoxybenzo[f]pyrrolo-[l,2-a]quinazolin-ll(lH) One in bis(dimethylamino)methane causing a vigorous exothermic reaction 2,3-dihydro-8-methoxy-l-methylenebenzo[f]pyrrolo[l,2-a]-... 

A few simple examples are the following. The interaction of o-amino-thiophenol and o-methoxybenzoic acid in polyphosphoric acid yields the expected benzothiazole (1 R= Me) at 160 °C, but results in the demethylated 2-(2-hydroxyphenyl)benzothiazole (1 R = H) at higher temperatures. Isatoic anhydride or the anhydride of an AW-(dicarboxy-... 

Sarcosin anhydride ( C H,oOsN ) + p-Methoxybenzoic acid ( CaHgOa )... 

Preparation by reaction of acetic anhydride with 4-hydroxy-3-methoxybenzo-phenone in the presence of pyridine in methylene chloride at r.t. for 15 min (94%) [1597]. 

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