Chroman structure

An interesting feature of 5-tocopherylacetic acid (51) and its derivatives was their appreciable thermal stability up to 200 °C. In contrast to 5a-substituted tocopherols carrying an electronegative substituent at C-5a, the homopolar C—C bond in the C2-unit at the 5-position of the tocopherol skeleton was shown to be very stable. Thermal decomposition of 51 at temperatures above 250 ° C caused a complete breakdown of the chroman structure, the C3-unit consisting of C-2, C-2a, and C-3 being eliminated as propyne, the side chain as 4,8,12-trimethyltridec-l-ene (Fig. 6.38). Fragmentation... 

Simon metabolites Initially, two major metabolites of a-tocopherol, the Simon metabolites (tocopheronic acid and tocopheronolactone) were described. Since they have a shortened side chain and an opened chroman structure, they are often quoted to demonstrate the antioxidant function of a-tocopherol in vivo. These metabolites are excreted in the urine as glucuronides or sulfates. The level of these metabolites increases markedly in the urine of healthy volunteers after a daily intake of 2 to 3 g all rac-a-tocopherol. 

This is an explanation for the fact that this type of vulcanization is not enabled by double bonds per se, without aUyic hydrogens in the elastomer molecules [4,74]. (It should be pointed out that the phenolic curative can also act by a slightly different mechanism to give crosslinks which contain chromane structural moieties [75], the allylic hydrogens stUl being required.)... 

Similar chromane structures (Fig. 4.13) can also be prepared by the reaction of abietic acid with diphenylolpropane [34]. 

Phenolic-modified alkyds are made by heating the alkyd with a low molecular weight resole phenolic resin based on p-alkylphenols. Presumably, the methylol groups on the phenols react with some of the imsatmated groups of the alkyd to form chroman structures. The resins give harder films with improved water and chemical resistance as compared to the immodified alkyd. 

The second type of mechanism, associated with Greth, suggests the formation of chroman structure between the benzene ring of the re-... 

Another structural type is chromenes. Centchroman [31477-60-8]is a pyrrolidinoethoxyplienyl chromane which is a potent antiestrogen with weak estrogenic activity. In India, it is used as a weekly contraceptive pih based on its reported abiUty to inhibit the uterine preparation for the attachment of the fertilized ova to the wall of the utems (see Contraceptives) (31). 

Unless great care is taken in control of phenol/acetone ratios, reaction conditions and the use of catalysts, a number of undesirable by-products may be obtained such as the o-,p- and o-,o- isomers of bis-phenol A and certain chroman-type structures. Although tolerable when the bis-phenol A is used in epoxy resins, these have adverse effects on both physical properties and the colour of polycarbonate resins. 

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. 

These observations indicated that an intermolecular double condensation to give a bis N-(methylene-4-oxocoumarinyl)-l,4 aromatic diamine had occurred. Data from the elemental analysis indicated that the calculated and observed values were within the acceptable limits ( 0.4%) and in conformity with the assigned structure. In the addition of molar equivalents of 1,4-aromatic binucleophilic compounds to compound 72 we did not observe any heterocyclic compounds resulting from the further intermolecular nucleophilic attack on the single condensation product. Since the condensation of 3-(dimethylaminomethylene)-chromane-2,4-dione with aromatic binucleophilic compounds is the only route to the new coumarinic compounds, this represents a useful synthetic method. 

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. 

When, furthermore, phenols (368) are coupled with 1 in the presence of a Pd° catalyst, the phenoxy-methyl-1,3-dienes 369 are produced [158]. As aryl allyl ethers, these can be made to undergo a Claisen rearrangement (205 °C, DMF) and the ensuing 2-(l,3-dienylmethyl)phenols 370 finally cydize in the presence of a trace of acid to a mixture of exo-methylene chromans 371 (major product) and dihydrobenzofur-ans 372 - a remarkable generation of functional and structural complexity from simple starting materials with 100% atom economy and underlining impressively the synthetic versatility of modern allene chemistry ... 

Addition of the hydroxyl group of the reduced ubiquinone or plastoquinone to the adjacent double bond leads to a chroman-6-ol structure. The compounds derived from ubiquinone in this way are called H ubichromanols (Fig. 15-24). 

The NMR spectra of various substituted chroman-4-ones occur in papers largely concerned with their synthesis. The spectra of some rotenoids such as (61), which contain the chromanone unit, have been analyzed and their structures elucidated (62JCS775,66JCS(C)542, 72JOC1636). 

Chroman-3-ones are not readily accessible and consequently there are few mass spectral data available. The major peaks in the spectrum of the parent compound appear at m/e 148 (M+ 53%) and at 92, 91 and 89 (73BSB283). The structures of the fragment ions and the pathways responsible for their formation have not been established. 

Interest in reduced pyrans centres around tetrahydropyrans and chromans. Many structural determinations have been reported for pyranoses and various derivatives (72PMH(5)l). 

Individual functional groups attached to a partially or fully reduced pyran ring behave much as expected of their aliphatic equivalents but there is often a quantitative difference in their reactivity which enables selective reactions to be carried out on polysubstituted compounds. Many examples of this are known in the tocopherol series which are the most important members of the chroman family. Since they are known by trivial names, these are shown with their structures (674). The most important tocopherol is natural vitamin E or a-tocopherol the four natural tocopherols have 7 -configuration at each of their asymmetric centres at C-2, C-4 and C-8. ... 

Figure D1.5.1 Structure of tocol 2-methyl-2-(4, 8, 12 -trimethyltridecyl)chroman-6-ol.

Tocopherols comprise a methyl-substituted chroman-6-ol ring attached at C-2 to a saturated iso-prenoid side chain. Tocotrienols are analogous structures whose side chains contain three trans double bonds. The tocopherols and tocotrienols are designated as a, (S, y, and 8, according to the number and position of the methyl substituents in the chromanol ring (Fig. 5). 

H-Benzo[a]carbazole, 4,4a,5,11,1 la,l lb-hexahydro-synthesis, 4, 283 Benzo[6]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 structure, 7, 735 sodium complex crystal structure, 7, 735 Benzo[ 18]cr own-6 membrane transport and, 7, 756 Benzo[6]cyclohepta[d]furans synthesis, 4, 106 Benzocycloheptathi azoles synthesis, S, 120... 

This effect was seen only in hypoxia, not normoxia, was dose-dependent within the range 0.2-200 /rM, and provided a simple in vitro model for investigating the mode of action of the vitamin. By examining the structure-activity relationship of the response, compounds with a phytyl side-chain, phytol and vitamin K-l (phytomenadione), of similar length to vitamin E (9) were found to be also active, but compounds that had structures which resembled the chroman ring of the vitamin, vitamin K-3 (menaphthone) and Trolox, were antagonists of the responses to the phytol side-chain effects. 

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