Pyranopyrandiones

Pyrano[4,3-6]pyran-2,5-dione, 7-methyl-aromaticity, 3, 639 Pyranopyrandiones aromaticity, 3, 639 dipole moments, 3, 627 synthesis, 3, 795 tautomerism, 3, 644 Pyranopyranones molecular structure, 3, 624 Pyranopyrans synthesis, 3, 760, 784 Pyranopyrazoles synthesis, 5, 321, 330 Pyranopyrazolones synthesis, 5, 334 Pyranopyridine synthesis, 3, 834 Pyranoses... 

The stereochemistries of papuanic and isopapuanic acids have been assigned on the basis of the structure and configuration of the pyranopyrandione (178) (68JOC4191). 

The observed dipole moments of a number of pyranopyrandiones also differ from the values calculated by vector addition. However, CNDO/2 calculated moments show a much closer agreement with the experimental values, as indeed does the value for pyran-4-one itself (76JHC609). 

Consideration of all the possible fusions between two 2- and/or 4-pyranone rings reveals that there are twenty possible pyranopyrandiones. These compounds are not readily accessible and comparatively few have been synthesized. Once again all are potentially aromatic. 

The carbonyl group frequencies in the IR spectra of pyranopyrandiones are characteristic of simple lactones (Figure 14). 

An MO study of all twenty pyranopyrandiones has been reported (73MI22200). Use was made of HMO calculations together with the co technique. Calculations were also performed on some methyl-substituted pyranopyrandiones and afforded values for the delocalization energy, 7r- bond orders and tt- charge densities. Empirical resonance energies were obtained... 

Figure 14 H NMR and IR data and resonance energies for some pyranopyrandiones (73M122200)...

A ring-chain tautomeric equilibrium between the pyranopyrandione (254) and the 4-pyranonecarboxylic acid (255 equation 9) in CDC13 solution has been investigated by H NMR spectroscopy (73AC(R)29l). The equilibrium constant Ki was calculated as 1.7 at 298 K and AH° for the equilibrium reaction as 16.2 kJ mol-1. 

Malonate derivatives have been used in the synthesis of pyranopyrandiones and dipyranopyrantriones, which are masked equivalents of triketo and tetraketo acids, respectively (Scheme 97) (66JA624, 67CC231). 

Cyclopropenones and carbon monoxide react in the presence of Ru3(CO)12 to form tetrasubstituted pyranopyr-andiones 655 in high yield (Equation 266) <2002JA6824>. Unsymmetrical tetrasubstituted pyranopyrandiones 656 can be accessed by the cross-carbonylation of cyclopropenones and internal alkynes in the presence of a ruthenium catalyst (Equation 267) <2002JA6824>. 

The reaction was extended to the cross-carbonylation of cyclopropenones and internal alkynes, leading to unsymmetrically substituted pyranopyrandiones (Eq. 18) [33]. 

Cyclobutenediones 148 possessing an alkoxy substituent reacted with norbornene 40 in quite a different way, in which CO molecule was extmded from the dione substrates (Scheme 4.52) [103]. In the presence of catalytic amounts of Ru3(CO)i2 and PEt3, 148 and 40 was heated at 160 °C under 3 atm CO to regioselectively afford cyclobutenones 149. Such a novel reconstructive cycloaddition was further extended to the carbonylative dimerization of a cyclopropenone 150 resulting in the formation of a pyranopyrandione 151 in high yields [104], These novel transformations of... 

In the presence of acetylenes, the latter are incorporated into the products to give unsymmetric pyranopyrandiones (Eq. 11.46). 

Treatment of dialkylcyclopropenones with catalytic amounts of Ru3(CO) 2 and EtgN under CO resulted in carbonylative dimerization of cyclopropenones to give pyranopyrandiones in good yields (Scheme 2.111) [169]. Cross-carbonylation of dipropylcyclopropenone with dec-5-yne resulted in unsymmetrically substituted pyranopyrandione 148. 

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