2.2- Dimethyl chromanes

Electron impact mass spectra of some natural products which possess a 2,2-dimethyl-chroman skeleton have been reported (690MS(2)965, 70OMS(3)94i). The mass spectra of the isomeric a-, /3-, and y-tocopherols have been reported (72MI22204). 

From the aerial parts of Evodia lepta, we isolated and identified thirteen 2,2-dimethyl-chromenes, four dichromenes, eight 2,2-dimethyl-chromans, one sesquiterpene and two fiavones. Figure 2 shows the extraction and isolation procedure. 

Formylation of 5,7-dihydroxy -( -propyl)-coumarin (1) provided on 8-formy-lated product (26). Treatment of the compound 26 with 3-chloro-3-methyl-l-butyne to introduce regioselectively the chromene 27 because the phenolic hydroxyl group at the C position was less accessible for formylated substitution because of a presumed hydrogen-bonding interaction. To construct the enantiomerically pure rra i-2,3-dimethyl chroman-4-ol system, Deshpande et al." ° used organoborone... 

Cycloaddition of COj with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiocheraistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /3-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. 

H-Benzo[a]carbazole, 4,4a,5,l 1,1 la,l Ib-hexahydro-synthesis, 4, 283 Benzo[b]carbazole, N-acetyl-photochemical rearrangements, 4, 204 Benzo[/]chroman-4-one, 9-hydroxy-2,2-dimethyl-synthesis, 3, 851 Benzochromanones synthesis, 3, 850, 851, 855 Benzochromones synthesis, 3, 821 Benzocinnoline-N-imide ring expansion, 7, 255 Benzocinnolines synthesis, 2, 69, 75 UV, 2, 127 Benzocoumarins synthesis, 3, 810 Benzo[15]crown-5 potassium complex crystal stmcture, 7, 735 sodium complex crystal stmcture, 7, 735 Benzo[ 18]cr own-6 membrane transport and, 7, 756 Benzo[b]cyclohepta[d]furans synthesis, 4, 106 Benzocycloheptathi azoles synthesis, 5, 120... 

Chroman, 6-hydroxy-2,2-dimethyl- C NMR, 3, 587 Chroman, 2-hydroxymethylene-synthesis, 3, 781... 

Chroman-3,4-diol, 7-methoxy-2,2-dimethyl-conformation, 3, 631 Chroman-3,4-diols IR spectra, 3, 595 Chromanochromanones... 

Chroman-4-one, 5-acetoxy-3-hydroxy-2,2-dimethyl-synthesis, 3, 857 Chroman-4-one, 3-amino-synthesis, 3, 855 Chroman-4-one, 3-benzylidene-synthesis, 3, 829 Chroman-4-one, 3-bromo-... 

Chroman-4-one, 3-bromo-2-hydroxy-synthesis, 3, 856 Chroman-4-one, 2-/-butyl- H NMR, 3, 583 Chroman-4-one, 3-/-butyl- H NMR, 3, 583 Chroman-4-one, 2,3-dibromo-dehydrobromination, 3, 828 Chroman-4-one, 3,3-dibromo-dehydrobromination, 3, 828 Chroman-4-one, 2,3-dihalogeno-synthesis, 3, 856 Chroman-4-one, 2,2-dimethyl-mass spectra, 3, 617 Chroman-4-one, 2,2-diphenyl-synthesis, 3, 852 Chroman-4-one, 3-hydroxy-synthesis, 3, 856... 

Chroman-2-ylmethanol, (5)-6-hydroxy-2,5,7,8-tetramethyl-synthesis, 3, 779 Chromene, 3-acetyl-2-methoxy-synthesis, 3, 750 Chromene, 2-alkyl-synthesis, 3, 749 Chromene, 4-aryloxymethyl-synthesis, 3, 742-743 Chromene, bis(2,2-dimethyl-mass spectra, 3, 604 Chromene, 2,3-dichloro-synthesis, 3, 753 Chromene, 2,2-dimethyl-IR spectra, 3, 594 mass Spectra, 3, 604 molecular dimensions, 3, 621 synthesis, 3, 743, 749, 751 Chromene, 3-fluoro-2,2-dimethyl-synthesis, 3, 748 Chromene, 5-hydroxy-synthesis, 3, 745... 

Paraxanthine—see Xanthine, 1,7-dimethyl-Parent name nomenclature, 1, 35 Parham cycloalkylation in chroman synthesis, 3, 783 Paromomycins as pharmaceuticals, 1, 154 Partial charge transfer from donor to acceptor stacks, 1, 350 Pasteurellosis... 

We also investigated reaction of 4-hydroxycoumarin with an excess of Ar,Ar-dimethylformamide dimethyl acetal (DMFDMA) which afforded the corresponding 3-(dimethylaminomethylene)-chromane-2,4-dione derivative 72. The structure was again confirmed by IR, NMR, and MS analyses. 

The oxidation behavior of 3-oxa-chromanols was mainly studied by means of the 2,4-dimethyl-substituted compound 2,4,5,7,8-pentamethylM /-benzo[ 1,3]dioxin-6-ol (59) applied as mixture of isomers 27a it showed an extreme dependence on the amount of coreacting water present. In aqueous media, 59 was oxidized by one oxidation equivalent to 2,5-dihydroxy-3,4,6-trimethyl-acetophenone (61) via 2-(l-hydroxyethyl)-3,5,6-trimethylbenzo-l,4-quinone (60) that could be isolated at low temperatures (Fig. 6.41). This detour explained why the seemingly quite inert benzyl ether position was oxidized while the labile hydroquinone structure remained intact. Two oxidation equivalents gave directly the corresponding para-quinone 62. Upon oxidation, C-2 of the 3-oxa-chroman system carrying the methyl substituent was always lost in the form of acetaldehyde. 

The reaction of 2-polyfluoroalkylchromones (e.g., 323) with l,3,3-dimethyl-3,4-dihydroisoquinolines (e.g., 324) gave zwitterionic 6,7-dihydrobenzo[ ]quinolizinium compounds such as 326 (Scheme 70). The mechanism proposed for this transformation involves an addition-elimination displacement of the chromane heterocyclic oxygen by the enamine tautomer of the dihydroisoquinoline, followed by intramolecular cyclization of the intermediate 325 <20030L3123>. 

Z/-l-Benzothiopyrans with catalytic amounts of acid undergo disproportionation to thiochromans and benzothiopyrylium salts. In the case of 3,4-dimethyl-2//-l-benzothiopyran, intermolecular hydride transfer yields an 85 15 mixture of cis- and intermediate bridged sulfonium ion has been suggested to be responsible for the stereochemical control of this reaction.276 Bromination of 2H-1-... 

The abundance of the [RDA + H]+ ion is markedly greater in chroman-4-ones with gem-dimethyl groups at C-2. Spectra of 2,2-dimethylchroman-4-ones with aromatic methoxy substituents have been studied (780MS653). All showed intense peaks corresponding... 

Studies of the conformations of chromans include those on 3,4-dihalogenochromans (189 X = Br) and 3-halogenochroman-4-ols (189 X = OH) (70JCS(C)1006), which have been summarized (81HC(36)169> together with the related 2,2-dimethyl derivatives <65JCS5049>. 

Bromination, chlorination, nitration and Friedel-Crafts acylation of chroman give the 6-substituted derivatives in good yields by standard methods. When 6,8-dimethyl-chromanone (677) is warmed with formaldehyde in sulfuric acid, hydroxymethylation at C-5 occurs (78BCJ1874). 

The reaction of 1,3-dihydroxynaphthalene with 3,3-dimethylacrylic acid in the presence of phosphorus oxychloride and zinc chloride yields only 9-hydroxy-2,2-dimethyl-benzo[/]chroman-4-one (585). 2,7-Dihydroxynaphthalene similarly yields the angular ben-zochromanone (586) rather than the alternative linear product (79RRC59). 

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