Triones, cycloaddition

Thermal decomposition of l,2-dihydro-477-pyrrolo[2,l-r-][l,4]benzoxazine-l,2,4-triones 425 yielded 7-(2,4,6-trimethylbenzoyl)-8-[(2,4,6-trimethylphenoxycarbonyl)-6,10-dihydropyrido[2,l-r-][l,4]benzoxazine-6,10-dione by [4+2] cycloaddition of the initially formed ketene 426 and the subsequent rearrangement of 6,8,9,10-tetrahydropyrido[2,l-c][l,4]benzoxazine-6,8,10-trione 427 (Scheme 36) <1999RCB2131>. 

A library of fifteen 6,7,9,9a-tetrahydro-57/-pyrazolo[l,2-tf]pyrrolo[3,4-ir]pyrazole-l,3,5(2/7,3a7/)-triones 712 was prepared by combinatorial stereoselective cycloadditions of compounds 320 to A-substituted maleimides. 

Heating tetrahydropyrrolo[l,2-rz]quinoxaline-l,2,4-trione 456 in decane at 172-173 °C provided 5,6-dihydro-10H-pyrido[l,2-a]quinoxaline-6,10-dione 459 via the [4+2] cycloaddition of primarily formed ketene 457 followed by the 1,3-migratiom of the COR group of 458 (05RJ01081). 

Lactones of azocarboxylic acids are remarkably reactive. In the presence of phenyl isocyanate, the imino isocyanate formed from reactive 2-hydrazono-A3-l,3,4-oxadiazolines via a 1,3-dipolar cycloreversion is intercepted to give [l,2,4]triazolo[l,2-a]-[l,2,4]triazole-l,3,5-triones by means of two subsequent [2 + 3] cycloadditions via azomethine imine intermediates (Scheme 10) (76T2685). 

A domino Knoevenagel/Diels-Alder epimerization sequence followed by Suzuki coupling provided a library of biphenyl and terphenyl spirocychc triones (Scheme 24) [58]. The initial Knoevenagel adducts 103 were formed from either 1,3-indandione or Meldrum s acid 101 and various bromosubstituted benzalde-hydes in the presence of catalytic (l)-5,5-dimethyl thiazolidinium-4-carboxylate (DMTC) in high yields. Diels-Alder cycloaddition of 103 with 104, formed in sim from 102 and (l)-DMTC, provided exclusively the cA-spiro compounds 105 due to epimerization of the minor trans isomer to the thermodynamically more stable cis. Subsequent Suzuki couplings of 105 with various boronic acids afforded the final compounds 106. 

Serratosa has critically evaluated the various entries to the triquinacene system available via Pauson-Khand chemistry, concluding that a route involving cycloaddition of the dibenzylated enyne substrate (Schemes 17 and 23) is operationally the simplest for preparation of multigram quantities of tricy-clo[5.2.1.0 °]decane-2,5,8-trione. This in turn is a key intermediate for the study of synthetic entries to dodecahedrane and its derivatives. An optically active version of this synthesis has l n developed as... 

It is reported that the formylpyrimidinedione (58) reacts with Schiff bases to yield the dihydropyrido[3,4-rf]pyrimidinediones (60), which are partially hydrolyzed to the triones (61) on workup (89MI1). A likely mechanism (Scheme 8) involves [4 + 2] cycloaddition of the imine to the tautomer (59), followed by dehydration. The trione (61, R = 2-furyl, = Ph) was assigned the structure shown, rather than the regioisomer, which might... 

Keywords Isatins, naphthaquinone, proline, ethyl lactate-water system, bio-based green solvent, room temperature, 1,3-dipolar cycloaddition, one-pot three-component reaction, spiro-oxindoles, spiro[benzo[/]pyrrolo[2,l-fl]isomdole-5,3 -indoline]-2, 6,ll-triones... 

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