Chromane analogs

In the above cases, the photoreactivity of indole, coumarin, pyridine, and so forth, does not compete effectively with PFR, which becomes the major reaction. However, in the case of the chromene depicted in Scheme 28, the electrocyclic ring opening prevails over PFR. By contrast, the analogous chromane undergoes clearly acyl migration [86]. 

The reaction of dehydrolinalool acetate (274) with the homocuprate of olivetol bis(tetrahydropyranyl ether) (273) was expected to yield cannabichromene by analogy with the reaction with 3-acetoxy-3-methylbut-l-yne (79JCS(Pl)20l). However, the major product was 3,4-m-A1,2-tetrahydrocannabinol (275), which could readily be purified, thereby providing a valuable route to this substance. Its formation is thought to involve the generation of an allene which proceeds to the chroman via an allylic cation and trans addition to the isopropylidene group (Scheme 69). 

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). 

Partially reduced pyrans are named as derivatives of 2//-pyran, for example, 3,4-di hydro-2//-pyran 13 and 3,6-dihydro-27/-pyran 14. The trivial name for the benzo analog 15 is chroman, and flavan is used for 2-phenyl... 

The acid-promoted rearrangement of the diazo-compound (130), prepared by the reaction of ethyl lithiodiazoacetate with isochroman-4-one, gave the new 2-benzoxepin system (131) a similar sequence, starting with chroman-4-one, gave the analogous 1-benzoxepin. Both were de-ethoxycarbonylated by a mild... 

Bisphenol A and analogous compounds yield 9,9-dimethylxanthones on reaction with substituted phenols in the presence of MeSOsH chroman (45) and spiroketal (46) are intermediates <97JOC1058>. 

The detailed structure of the clathrate compound formed between 2,5,5-trimethylhex-3-yn-2-ol and 4-p hydroxyphenyl-2,2,4-trimethylthio> chroman has been determined by A -ray crystallography. tra/i5 -3,4-Dibromothiochroman and analogous dibromo-naphthothio-pyrans, prepared by addition of bromine to the appropriate A -thio-chromenes, may exist in sofa conformations. The dibromo-compounds undergo ring-contraction reactions with alkalis, yielding benzo[ ]thiophen derivatives. ... 

Figure 17. a) Comparison of the modelled and experimentally determined conformations of the chroman-linked inhibitor (S,S)-17 bound to thermolysin (the modeled inhibitor lacks the methyl substituent on the aromatic ring), b) Comparison between the bound conformations of the cyclic inhibitor (S,S)-17 and acyclic analog 19. 

Other natural precocenes and synthetic analogs have been prepared and biologically evaluated (Isman, 1989). Synthetic chromanes showed significantly less activity than the parent chromenes (precocenes) while the acetylchromenes showed antijuvenile hormone... 

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