Dimers chromonics

Dimer of 3,4-dihydro-4-(4 -hydroxyphenyl)-7-hydroxycoumarin. No data of the positive control (92) was reported. 6 4,4 -Dihydroxy-2,6-dimethoxydhihydrochalcone. c 5,7-Dihydroxy-3-(4-hydroxybenzyl)-4-chromone. 

Simple chromones are less susceptible to photolysis but 3,5,7-trimethoxy-2-methyl-chromone (369) is converted into a dimer which may have structure (370) (73TL5073). The 3-benzylchromone (371) is cyclized to the tetracycline analogue (372) (72JCS(P1)1103). 

Photodimerizations have been observed in a variety of sulfur-containing heterocycles notable examples include the photodimerization of 2- and 3-ary lbenzo[b]thiophens,287 benzo[h]thiophen 1-oxide,288 benzo[h]thiophen 1,1-dioxide,289 and its 2-bromo289 and 2-methyl derivatives.290 All four possible dimers were obtained on irradiation of thio-chromone in aromatic solvents,291 and 1-thiauracil (345) is converted into... 

The formation of dimeric oxetanol 319 was observed upon irradiation of 2,7-dimethyl-3-methoxychromone 318 (Scheme 44) <1996T7855>. Interestingly, irradiation of chromones with no substituents on the benzene ring led to the formation of demethoxylated products (e.g., 321). 

The kinetics of the addition of ketene dimer to aromatio amines havo been mvostigated. The dimers of the higher alkylketenes do not react with secondary amines or with phmiyUiydraiine, but their quantitative reaction with ethylamine hae been used for their determination, 2,3-J)ihydro-A, A diiii thyl-p-tketene dimer to form 7.8-dihydio-2,6 dimethy1-chromone. 

The sensitized irradiation (acetophenone) of the coumarin (104) yields two dimers which have been identified as (105) and (106). ° All four possible dimers (107, 108) are obtained from the irradiation of the thio-chromone (109) in aromatic solvents. In contrast the sulphone (110) is unreactive. ... 

Intramolecular Wittig-type cyclizations have been used successfully in many ring-synthesis applications, and some further examples reported this year include the preparation of chromones by cyclization of the carbonate (149) and an indole synthesis from O-acyl benzyltriphenylphosphonium salts. The bicyclo[3.3.0]oct-A -en-3-one ring system lacking substituents at C-2 and C-5 is produced by ring closure of the phosphonates (150), although in the case of the parent member of the series (150, R = R = H) a novel dimer is formed... 

Simple isodesmic behavior (Fig. 4) is expected to be characteristic of chromonic systems, and this appears to be generally true. However, the situation can be more complex. Extensive studies of dye/water systems have shown that there is sometimes a distinct threshold concentration with some resemblance to the amphiphile cmc, where dimers first appear [41]. 

Luckhurst potential, dimers 816 luminance, guest-host effect 272 lutetium, phthalocyanine ligands 924 lyotropic blue phases, chromonics 998 lyotropic systems... 

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