Azulenes acylation

The Friedel-Crafts acylation at the 3-position of the azulene ring was possible due to the effect of the electron-withdrawing 1-methoxycarbonyl group. 183 has been prepared previously in an eight-step synthetic route in an unsatisfactory reaction yield156. 

Perfluoroaikanoyl chlorides and anhydrides are also acylating agents Tri-fluoroacetic anhydride acylates a number of pyrroles, thiophenes, and fiirans without a catalyst [37, 38, 39] Azulene can be diacylated without a catalyst m 12 h [40] (equation 26). 

In keeping with its aromatic character and unsymmetrical charge distribution, azulene undergoes certain typical electrophilic substitution reactions at the 1 and 3 positions. Thus Friedel-Crafts acylation leads to a mixture of 1-ethanoylazulene and 1,3-diethanoylazulene ... 

Lithium alkyls or aryls add to pseudoazulenes 3398100 and 39.113-114 The carbanion always reacts with the carbon atom opposite the heteroatom in the six-membered ring (Scheme 16). After hydrolysis of primary intermediate 121 dihydro products (122) are formed, which can be transformed to pseudoazulenes in the usual manner (see Section III,A,2). The structure of primary intermediate 121 is confirmed by its alkylated (or acylated) products (123). Even these compounds can easily be dehydrogenated to pseudo-azulene. In this way. substituted pseudoazulenes can be formed that are not obtainable otherwise. The direction of addition to the pseudoazulenes is the same as in azulenes.241... 

The fact that, in the reaction formulated above, anisole yields the acetyl and not the trifluoroacetyl derivative means that the mixed anhydride is a more reactive acylating agent than trifluoroacetic anhydride. However, the pure anhydride alone is capable of effecting acylation. It reacts with azulene (blue) in carbon tetrachloride without catalyst at room temperature to give 1-trifluoroacetylazulene (red) in high yield. "... 

Benzanilide and phosgene have been used to introduce a benzoyl group into dimethylaniline (85% yield) 828 and other acylations can be effected analogously, as when ethyl 8-(l-azulenyl)-8-oxooctanoate is obtained in 80% yield from azulene, ethyl 7-(Ar,Ar-dimethylcarbamoyl)heptanoate, and phos-phoryl chloride.855... 

Electrophilic aromatic substitution reactions of compounds 10 occur in a fashion characteristic for heterocyclic analogues of azulene, and are specific at positions 5 and 7 <1994CB1479>. Thus, 10a (R = H, R = Ph) was successfully brominated, formylated, and acylated, as shown in Scheme 7. 

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