1 H-2-Benzopyrans

Figure 6.24 The stepwise process used to draw the structure of 3,4-dihydro-1-methyl-1 H-2-benzopyran.

The 1/7-2-benzopyran-l-one or 1/7-2-benzothiapyran-l-one (1.0 g) in EtOH (50 mL) containing hydrazine hydrate (2 mL, large excess) was heated under reflux for 2 h. The resulting solution was evaporated and the residue was recrystallized (EtOH). 

Many natural isocoumarins have been assigned trivial names and these are listed in the Tables and the Trivial Name Index. The numbering system of the isocoumarin ring system has led to some confusion in the past (525) the preferred system is given above and agrees with that used for the lUPAC and Chemical Abstracts preferred name H-2-benzopyran-1 -one. 

Shimojima, Y., and H. Hayashi lH-2-Benzopyran-l-one derivatives, Microbial Products with Pharmacological Activity. Relationships between Structure and Activity in 6-[[l S-(3S,4-Dihydro-8-hydroxy-l-0X0-1 H-2-benzopyranon-3-yl-3-methylbu-tyl]amino]-4S,5S-dihydroxy-6-oxo-3S-ammoniohexanate. J. Med. Chem. 26, 1370 (1983). 

Cyclocondensation of 3-formyl-4/f-l-benzopyran-4-ones (147) with 5 in refluxing benzene containing p-toluenesulfonic acid gave 5a,ll-dihydro-17>H-[ 1 ]benzopyrano[2,3-6][ 1,5]benzothiazepin-13-ones (148) in 70-81%... 

A solution of 109.8 g (0.75 mol) of diethyl oxalate and 65 g (0.427 mol) of 2, 4 -dihydroxyacetophenone in 100 mL of EtOH was added slowly under Ar, with cooling, to a stirred solution of NaOEt (from 40 g of Na and 550 mL of EtOH). The mixture was stirred at 50°C for 3 h, cooled to room temperature, and poured into a separatory funnel containing 500 mL of 2 N HCI. It was extracted with CH2CH2 washed with 500 mL of saturated NaHC03, dried and evaporated to give a red oil, which was dissolved in 250 mL of EtOH and 10 mL of cone. HCI. The mixture was boiled under reflux for 1 h, cooled to ca. 10°C and the product was collected by filtration. It was washed with some EtOH followed by hexane to give 86.0 g (86% yield) of ethyl 7-hydroxy-4-oxo-4H-l-benzopyran-2-carboxylate m.p. 218-223°C. Crystallization of a portion from hot AcOH gave an analytical sample m.p. 221-223°C. 

Intramolecular alkoxycarbonylation of secondary benzylic alcohols (e.g., 3) requires a shorter time (2 h) and a mixture of 1,3-disubstituted 3,4-dihydro-1 //-2-benzopyrans 4 is obtained in 82% yield and a 74 26 (cis/trans) diastereomeric ratio, as determined by HPLC. The stereochemistry of each isomer is determined by a comparison with known compounds84,85. 

Benzopyrone reagieren analog zu (2-Hydroxy-phenyl)-1 H-pyrazolen,185 1191,1364, i365, 1377 [tabellarische Zusammenstellung s. Bd.Vl/lc, S. 397/398 sowie S. 453, 1460 (1976) und Bd.X/2, S.6798 (1968)], 2-Methyl-4-thiono-4H-l-benzopyran gibt mit Hydrazin bzw. Phenyl-hydrazin 3(5)-(2-Hydroxy-phenyl)-5(3)-methyl- bzw. 5-(2-Hydroxy-phenyl)-3-methyl-l-phe-nyl-lH-pyrazol [s. Bd. IX, S. 725 (1955)]. 3-Formyl-4H-l-benzopyrone geben mit Phenyl-hydr-azin 4-(2-Hydroxy-benzoyl)- -phenyl -1 H-pyrazole1186 ... 

H-furo[2,3-h]-t-benzopyran-2-one 2,3-dihydro-3,4-di-hydrOxy -2 ( I -hydroxy -1 -methylethyl) -5 -benzofuranacrylic acid S-lactone diisovalerate. mol wt 430.48, C... 

T)-2-(4-hydroxyphenyl)ethcnyl]-4,7-dimcthoxy-3-methy 1-2 H-1 -benzopyran-2-one Ekebergia benguelensis 65... 

---