6- Hydroxy-2- benzofuran

Chromanone, 3-acetamido-2-methyl-reduction, 3, 729 Chromanone, 3-amino-synthesis, 3, 734 Chromanone, 3-arylidene-thermoisomerization, 3, 722 Chromanone, 3-benzylidene-thermolysis, 3, 728 Chromanone, 3-bromo-2-hydroxy-benzofuran from, 3, 729 Chromanone, 6,8-dimethyl-hydroxymethylation, 3, 731 Chromanone, 2,3-epoxy-as synthon, 3, 735... 

There are only few representatives of 79. When 2,3-diphenyl-7-hydroxy-benzofuran was oxidized with Fremy s salt, a mixture of the 6,7- and 4,7-dione was obtained (70MI2). Similarly, nitric acid oxidation of the dihydroxy precursor afforded the quinone 82 or the related 5,6-dione, corresponding to the system 81 (12LA384). 

The application of the above method to the syntheses of insecticides carbamates Carbofuran (entry 4, table 3-27) and Aldicarbe was briefly studied. Thus, Carbofuran was readily obtained in 79% yield from 1-chloroethyl benzofu-ranyl carbonate which was itself obtained in 89% yield from the corresponding hydroxy benzofuran. 

Formation of the methylcarbamate of 2,3-dihydro-2,2- dimethyl-4-hydroxy benzofuran in 57% yield has been reported from the N-methylamido derivative of saccharin through nucleophilic substitution by the addition of triethylamine in aqueous acetone (1 2) at ambient temperature over 2 hours (ref.29). 

The benzene ring of benzofurans can also be built up by elimination reactions from suitably substituted precursors. Treatment of (78), which is available from l,3-diketo-5-phenylcyclohexane and ethyl a-chloroacetoacetate and subsequent bromination with base, yields a 4-hydroxy-benzofuran (Scheme 71) <76CHE733, 76KGS879). 

Dihydroxybenzoyl)acrylic acid, 95 3-(2, 4 -Dihydroxybenzolymethyl)-6-hydroxy-benzofuran-2-one, 96 Diimide, MA reducing agent, 42 Diisobutylene... 

Obtained by photooxygenation of 2,3-dimethyl-5-hydroxy-benzofuran in methylene chloride at -5° (10%) [2896]. 

Isotubaic acid — see Benzofuran-5-carboxylic acid, 4-hydroxy-2-isopropyl-Isouramil occurrence, 3, 144 5-Isoxalones potentiometry, 6, 11 Isoxanthopterin, 6-acetonyl-structure, 3, 276 Isoxanthopterin, 3,8-dimethyl-rearrangements, 3, 309 Isoxanthopterin, 6-methoxy-3,8-dimethyl-synthesis, 3, 297 Isoxanthopterin, 6-methyl-bromination, 3, 301 Isoxanthopterin, 8-methyl-synthesis, 3, 319 Isoxanthopterin, 6-phenacyl-structure, 3, 276... 

It was reported that the eorresponding 2-hydroxy-3-aeetyl-benzofuran exists entirely in the enol form (73AJC1079 84H737 87CC1150) [produees deep blue eolor with ferrie ehloride (55JA1623)].This is in aeeordanee with AMI, PM3, and B3LYP/6-31G ealeulations for 3-formyl-2-hydroxybenzo [h]furan as model eompound (99UP1) (see Seheme 10, all values in keal/mol). 

Fluorophenyl)-l ]-hydroxy-2,3,4,1 ]-tetrahydro-6/7-pyrimido[],2-Z)]-isoquinolin-6-one was obtained in the reaction of l-(4-fluorophenyl)-3-oxo-],3-dihydro-2-benzofuran-l-carboxamide and 1,3-diaminopropane in boiling toluene (01BMCL339). 

Chemical Name 2-Acetyl-7-(2-hydroxy-3-isopropylaminopropoxy)benzofuran Common Name —... 

Furoquinones, such as naphtho[2,3-b]fiiran-4,9-dione, naphtho[l,2-b]fiiran-4,5-dione, benzofuran-4,7-dione and benzofiiran-4,5-dione derivatives are available by the ceric ammonium nitrate mediated [3+2] cycloaddition of 2-hydroxy-1,4-naphthoquinones and 2-hydroxy-1,4-benzoquinones with alkenes or phenylacetylene <96CL451>. 

When these cycloaddition reactions are carried out with alkynes, furan derivatives are formed. lodonium ylide 5, for instance, on photochemical reaction with alkynes 43, gives benzofurans 44 (86JOC3453) (Eq. 19). In a similar way, the iodonium ylide derived from 2-hydroxy-1,4-naphthoquinone undergoes a cycloaddition reaction with phenylacety-lene to yield benzofuran 45 (Scheme 16) (89LA167). 

Bioassay-guided fractionation of a phytotoxic extract led to the isolation of two major phytotoxic agents (Fig. 8) characterized as 2 -(2 -hydroxy-4 -methylphenyl)-2 -oxoethyl acetate and designated with the trivial names of hofmeisterin (29) and 3 4 4tz 9rz -tetrahydro-6,7 -dimethylspiro [benzofuran-3(2//), 2 -pyrano [2, 3- ] benzofuran]-2, Aa -diol (30), along with several inactive compounds. 

Methoxy-6-propyl-l,4-benzoquinone (170, Scheme 43) with hydrogen chloride undergoes dimerization and yields the biquinone 171 and the di-benzofuran 172. 2-Hydroxy-3,6-dimethyl-1,4-benzoquinone (173, Scheme 44), however, on treatment with boron trifluoride etherate in ether, or with concentrated sulfuric acid in acetic acid at room temperature, yields the extended quinone 174, which on reductive acetylation affords the dibenzo-furan 175. 

Out of a series of 42 compounds isolated and characterized in our investigation on B. papyrifera [41], comprising benzofurans, coumarins, and various types of flavonoids (biphenylpropanes, chalcones, flavans, flavanones, and flavones), only certain representatives of the latter class of compounds showed potent aromatase inhibition activity (Table 2). Flavanone 39 (2S)-2, 4 -dihydroxy-2"-(l -hydroxy- 1-methylethyl)-... 

In a follow-up communication,26 similar chemistry was used for the production of 2-substituted benzofurans beginning not with an anthranilic acid derivative, but with a resin-bound ortho-hydroxy aryl iodide 3. In the solid-phase work, depicted in Scheme 5, the relevant carboxylic acid was linked to TentaGel via a Mitsunobu reaction, and after deprotection was seen to undergo smooth Heck coupling and cyclization, giving essentially pure compounds in 40-70% overall yield after cleavage. 

Equilibrium and rate constants for the keto-enol tautomerization of 3-hydroxy-indoles and -pyrroles are collected in Table 32 (86TL3275). The pyrroles ketonize substantially (103-104 times) faster than their sulfur or oxygen analogues, and faster still than the benzo-fused systems, indole, benzofuran, and benzothiophene. The rate of ketonization of the hydroxy-thiophenes and -benzothiophenes in acetonitrile-water (9 1) is as follows 2-hydroxybenzo[b]thiophene > 2,5-dihydroxythiophene > 2-hydroxythiophene > 3-hydroxybenzo[/ Jthiophene > 3-hydroxythiophene. 3-Hydroxythiophene does not ketonize readily in the above solvent system, but in 1 1 acetonitrile-water, it ketonizes 6.5 times slower than 2-hydroxythiophene (87PAC1577). 

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