2,3-dihydrobenzofuran carboxylic

Efaroxan, an a2 adrenoreceptor antagonist, could be used for the treatment of neurodegenerative diseases (Alzheimer and Parkinson), migraine and type II diabetes. Therefore, the total syntheses of ( + )-efaroxan and their derivatives have drawn much attention.The chiral 2,3-dihydrobenzofuran carboxylic acid 135, the direct precursor of (+ )-efaroxan, was obtained mainly from the resolution of racemic 135. Coelho el al. have reported a straightforward enantioselective synthesis of i -( + )-2-ethyl-2,3-dihydrofuran-2-carboxylic acid (135) achieved by a Sharpless-Katsuki asymmetric epoxidation reaction (Scheme 5.22). The dihydrobenzofuran acid 135 was obtained in seven steps from MBH adduct 136 in an overall yield of 17%. 

As the dihydrobenzofuran carboxylic acid 1 is a penultimate intermediate in the synthesis of R108512, it is essential that this compound doesn t contain any impurities that might impact the final API (active pharmaceutical ingridient) purity. This goal was achieved by isolating the sodium salt of compound 1 prior... 

The Smith group, in 2011, developed a highly diastereo- and enanhoselective intramolecular Michael addition/lactonization reaction. The authors applied a chiral tetramisole (74) to catalyze the cyclization of multifunctional substrates 75 or 77, affording fused indanes 76 or dihydrobenzofuran carboxylates 78, respectively, in good yields and with excellent ees (Scheme 36.20) [26]. 

A very impressive application of this chemistry is the total synthesis of (—)-ephedradine A 102.222 The key intermediate /rcarboxylic acid ester 101 was synthesized by intramolecular C-H insertion reaction. Upon treatment with a catalytic amount of Rh2(Y-DOSP)4, aryl diazo ester 100 possessing a chiral auxiliary underwent a C-H insertion reaction to give 101 in 63% yield and 86% de (Equation (83)). 

Amino-2,3-dihydrobenzofurans such as (501) and (502) are useful as antidepressants and hypotensives (70USP3513239). Substituted 5-acyl-2,3-dihydrobenzofuran-2-carboxylic acids of the type (503) possess diuretic and antitussive activities (69GEP1927393). Derivatives of the 3-phenyl-2 (3H)-benzofuranone type (504) exhibit musculotropic and anaesthetic effects. Amethone (505) is used against bronchial asthma and also shows antihistaminic activity (47JA980). 

A mixture of the 2-hydroxy-5-chloro-3-(2-methyl-2-propenyl)benzoic acid, methyl ester and 1 L of methanol was saturated with 90% formic acid and then refluxed overnight. The solution was concentrated in vacuum, added to water, and extracted with ethyl acetate. The organic layer was washed with water, dried over sodium sulfate, and concentrated in vacuum, providing the desired 2,2-dimethyl-5-chloro-2,3-dihydrobenzofuran-7-carboxylic acid, methyl ester as an oil. 

A mixture of 2,2-dimethyl-5-chloro-2,3-dihydrobenzofuran-7-carboxylic acid and thionyl chloride was heated at reflux for 3 h. After the mixture was... 

Flavanones undergo a variety of transformations by HTI or other hypervalent iodine reagents. In methanol, at room temperature, they were dehydrogenated to the corresponding flavones [40], A similar dehydrogenation occurred in chromanones [41]. Dramatic solvent effects occurred when methanol was replaced by other solvents. Thus, in trimethyl orthoformate ring-contraction was the main pathway and methyl 2-aryl-2,3-dihydrobenzofuran-3-carboxylates the major products, accompanied by substantial amounts of 3-methoxyflavones [42] ... 

The synthesis of ZK 216348 (Figure 9.5) starts from the commercially available dihydrobenzofuran. Deprotonation and carboxylation provides the 7-carboxylic acid which is transformed into its ester. Grignard reaction gives the tertiary alcohol. Treatment with trimethylsilylenolether, followed by saponification, affords the... 

Coumarins are known to react with amines to give various products, for example 2,3-dihydrobenzofurans. 3-Bromocoumarin has been shown to give the benzofuran (194) on heating with piperidine but coumarin itself gave 2 -hydroxycinnamic acid amides. The behaviour of coumarin-3-carboxylic acid with amines depends on the ratio of reactants and the temperature. When 8-acetyl-7-hy(iroxy-4-methylcoumarin was subjected to a Mannich reaction, the benzodipyran (195) was formed in 80% yield.Several other tricyclic products have been prepared from coumarins for example, the... 

Ring contraction of chroman-4-ones. In the same fashion as the formation of arylacetic esters from open-chain phenones, dihydrobenzofuran-3-carboxylic esters are obtained when chroman-4-ones are oxidized with TTN in the presence of... 

In the case of the related compound 6,7-dichloro-2,3-dihydro-5-(2-thienylcarbonyl)-2-benzofurancarboxylic acid (Fig. 10), the diuretic and uricosuric properties are essentially completely separated. The (+)-5 -enan-tiomer, possessing the natriuretic activity, is twice as active as the racemate, with the uricosuric activity residing in the (—)-i -enantiomer [75,76]. It was postulated that a mixture of the two enantiomers could be prepared to yield an appropriate balance between the two actions [76]. Examination of nonracemic mixtures of the individual enantiomers in the chimpanzee resulted in the conclusion that the racemate possesses the optimal therapeutic ratio of the diuretic and uricosuric properties [75]. However, compared to humans the chimpanzee is a hyperresponder to uricosuric compounds and thus it may not be possible to extend this observation to man. A similar differentiation in enantiomeric activity has also been observed for the related compound 5-dimethylsulphamyl-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid (DBCA) (Fig. 10), the uricosuric and diuretic activities being associated with the (+)-7 - and (—)-5-enantiomers, respectively [77]. 

Senboku H, Michinishi J, Kara S (2011) Facile synthesis of 2,3-dihydrobenzofuran-3-ylacetic acids by novel electrochemical sequential aryl radical cycliza-tion-carboxylation of 2-allyloxybromobenzenes using methyl 4-tert-butylbenzoate as an electron-transfer mediator. Synlett 1567-1572. doi 10.1055/ s-0030-1260794... 

Other Heteroatom Nucleophiles. Alcohols and carboxylic acids also add to metal-activated alkenes, and processes for the industrial conversion of ethylene to vinyl acetate and acetals are well established. However, these processes have not been extensively used with more cort5)lex alkenes. In contrast, a number of intramolecular versions of the processes have been developed, a few examples of which are given here. Allylphenols cyclize readily in the presence of palladium(II) to form benzofurans (eq 4). Catalytic amounts of palladium acetate can be used if the reaction is carried out under 1 atm of molecular oxygen with copper diacetate as cooxidant, or in the presence of tert-butyl hydroperoxide. If instead of palladium acetate a chiral jr-allylpalladium acetate complex is used, the cyclization proceeds to yield 2-vinyl-2,3-dihydrobenzofuran with up to 26% ee. ... 

Kurosawa W, Kan T, Fukuyama T. An efficient synthesis of optically active trani -2-aryl-2,3-dihydrobenzofuran-3-carboxylic acid esters via C—H insertion reaction. Synlett 2003 1028-1030. 

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