The synthesis and reactions of some substituted cyclopent-4-ene-1,3-diones.

摘要

Oxocarbons are a series of compounds whose structures can be described as cyclic oligomers of carbon monoxide:(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)These compounds demonstrate unusually small pKa values for being carbon based acids. The determination of the pKa values of these acids, which reflects the stability of the ions formed is complicated by the presence of multiple equilibria involving the ionized species in aqueous solution. To circumvent this problem one of the hydroxyl groups in the oxocarbon was replaced by a methyl group to separate the interference caused by successive ionization of the first and second protons in these compounds. Ionization of a second proton from the methyl group, although greatly attenuated, could still be detected by nmr H/D exchange studies. This method of methyl substitution and nmr H/D exchange studies was successfully applied to hydroxy methyl cyclobutenedione. Application of this same methodology to the corresponding 5-membered ring oxocarbon requires the synthesis of the hydroxy methyl cyclopentene-1,2,3-trione.; A goal of this research was the synthesis of this material. Our efforts resulted in the synthesis of 2-diazo-4-methoxy-{dollar}5 {dollar}-methylcyclopent-4-ene-1,3-dione:(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)as an interesting and extremely reactive intermediate. The thermal, photochemical and transition metal catalyzed reactions of this material were then studied, in an effort both to prepare the desired oxocarbon derivative and to explore the chemistry of the diazo dione. In hydrocarbon solvents, products of addition and insertion were generally observed. These products were characterized and some of their chemistry was explored. In benzene, for example, two rather unique diastereomeric spironorcaradienes were formed which were demonstrated to be rapidly interconverting, along with the products of C-H bond insertion. The reactions of the diazo dione with heteroatom containing substrates, such as alcohols, mineral acids and simple carboxylic acids generated the expected heteroatom-H bond insertion products.; A series of oxidation reactions of 4-hydroxy-5-methylcyclopent-{dollar}4 {dollar}-ene-1,3-dione:(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)were examined to determine if direct oxidation to the trione could be achieved. The direct oxidation sequences examined involved the use of selenium dioxide and oxaziridines and were not successful in producing a characterizable product.