4-Allylbenzoic acid

A greater variety of substituted isocoumarins is available from the reaction of 7r-allylnickel halides with the sodium salts of 2-bromobenzoic acids. Use of the sodium salt is necessary to prevent debromination through an intramolecular proton transfer from the carboxyl group. The initial products, 2-allylbenzoic acids, undergo a palladium-assisted ring closure to isocoumarins. 

In a related manner, sodium 2-bromobenzoates have been converted into 2-allylbenzoic acids. A palladium-catalyzed cyclization involving nucleophilic attack of the carboxylate on the palladium-complexed alkene yielded an isocoumarin. However, in situ catalytic hydrogenation results in the formation of an isochroman-l-one. 

In 2003, Stoltz at CalTech described a palladium-catalyzed oxidative Wacker cyclization of o-allylphenols such as 55 in nonpolar organic solvents with molecular oxygen to afford dihydrobenzofurans such as 56.44 Interestingly, when (-)-sparteine was used in place of pyridine, dihydrobenzofuran 56 was produced asymmetrically. The ee reached 90% when Ca(OH)2 was added as an additive. Stoltz considered it a stepping stone to asymmetric aerobic cyclizations. In 2004, Mufiiz carried out aerobic, intramolecular Wacker-type cyclization reactions similar to 55—>56 using palladium-carbene catalysts.45 Hiyashi et al. investigated the stereochemistry at the oxypalladation step in the Wacker-type oxidative cyclization of an o-allylphenol. Like o-allylphenol, o-allylbenzoic acid 57 underwent the Wacker-type oxidative cyclization to afford lactone 58.47... 

Reaction of the sodium salts of 2-bromobenzoic acids with -Tr-allylnickel complexes gives the 2-allylbenzoic acids (68) which on treatment with PdClj cyclize to the isocoumarins (69) in good yields.The reaction, which occurs under very... 

The synthesis of the four monocarboxylic acids of dibenzothiophene has been recorded in the previous review. However, several modified preparations have since been described. Ethyl 1-dibenzothiophene-carboxylate has been synthesized from 2-allylbenzo[6]thiophene (Section IV,B, 1) hydrolysis afforded the 1-acid (57% overall). In a similar manner, 3-methyl-1-dibenzothiophenecarboxylic acid was obtained from the appropriately substituted allyl compound. This method is now the preferred way of introducing a carbon-containing substituent into the 1-position of dibenzothiophene. 2-Dibenzothiophenecarboxylic acid has been prepared by oxidation of the corresponding aldehyde or by sodium hypoiodite oxidation of the corresponding acetyl compound. Reaction of 2-acetyldibenzothiophene with anhydrous pyridine and iodine yields the acetyl pyridinium salt (132) (92%), hydrolysis of which yields the 2-acid (85%). The same sequence has been carried out on 2-acetyldibenzothiophene 5,5-dioxide. The most efficient method of preparing the 2-acid is via carbonation of 2-lithio-... 

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