Subject tropolones

Uchida T, Nemoto T, Yui T et al (1979) Use of technetium-99m as a radioactive label to study migratory patterns of leukocytes. J Nucl Med 20 1197-2000 Vallabhajosula S, Machac J, Goldsmith SJ et al (1986) Indium platelet kinetics in normal human subjects tropolone versus oxine methods. J Nucl Med 27 1669-1674... 

The present procedure, based on the last method, is relatively simple and uses inexpensive starting materials. Step A exemplifies the 2 + 2 cycloaddition of dichloroketene to an olefin, " and the specific cycloadduct obtained has proved to be a useful intermediate in other syntheses. Step B has been the subject of several mechanistic studies, and its yield has been greatly improved by the isolation technique described above. This synthesis has also been extended to the preparation of various tropolone derivatives. " ... 

Theoretically, the regioselectivity observed in photochemical [2 + 2] cycloaddition of 56 with 1,1-dimethoxyethene is in good agreement with experimental results and has been explained on the basis of pertubational molecular orbital theory." Hartke and co-workers" described an interesting contrast in the reactivity of tropolones in an intramolecular Diels-Alder reaction (Scheme 6.18). Thus, alkylation of 64a and 64b with 65 gave 66a and 66b, respectively, that were subjected to cyclization in refluxing toluene. Whereas 66a decomposed under the reaction conditions, 66b afforded 67b in high yield. 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with N-bromosuccinimide from cyclo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - The present procedure, based on the last method, is relatively simple and uses inexpensive starting materials. Step A exemplifies the 2 + 2 cycloaddition of dichloroketene to an olefin, " and the specific oycloadduot obtained has proved to be a useful intermediate in other syntheses. " Step B has been the subject of several mechanistic studies, " and its yield has been greatly improved by the isolation technique described above. This synthesis has also been extended to the preparation of various tropolone derivatives. - " ... 

Imembrine, a tropolone natural product related to colchicine was also synthesized via an oxazole-acetylene Diels-Alder reaction followed by a [4 -H 3]-oxyallyl cycloaddition.Here, 8-iodo-5,6,7-trimethoxyisoquinoline 269 was converted to 5-substituted oxazole 270 in four steps and 42% overall yield (Fig. 3.81). Thermolysis of 270 in refluxing o-dichlorobenzene effected the desired intramolecular Diels-Alder cycloaddition with concomitant loss of the Boc-protecting group to afford the tetracyclic furan 271 in 90% yield. At this point, 271 was subjected to the [4 + 3] cycloaddition in the presence of l,3,3-trichloro-2-propanone and 2,2,2-trifluoroethanol. Subsequent dechlorination of the intermediate (not shown) with zinc provided the oxabicyclic 272 as a single regioisomer in 73% yield. The synthesis of imembrine was completed in three steps from 272. 

A related reaction type is the high pressure (6.2 kbar) Diels-Alder reaction of 2-pyrones with cyclopropenone ketals 16 to give isolable bicycloadducts 17, which then undergo cycloreversion, electrocyclic rearrangement, and ketal hydrolysis leading to tropones. Tropolones also have been formed in this way. This tropolone annulation chemistry was the partial subject of a review in 1990, and it was exploited in the syntheses of some naturally occurring tropoloisoquinolines 18-20. ... 

In light of the rapid development in this field and the literature on other ligands for the sensitization of NIR luminescence being explosively growing, a selection of the work most representative has been made. Simpler ligands such as the Schiff base salophen, tropolonate, azulene dicarboxylate, or pyridine carboxylate molecules have been the subject of a recent review. Petoud et al. successfrilly... 

---