Pyranone analogs

Compounds in carbohydrate-based synthesis of 2,3-dihydro-4//-pyranones as starting compounds for the preparation of C-saccharides, glycosylstan-nanes, and analogs of tromboxane A2. 98EJ02267. 

Scheme 150).225 227 The pyran products predominate when the ratio of triphenylphosphine to palladium catalyst exceeds two whereas the linear oligomers are the major products when this ratio is close to unity. The suggested227 mechanism (Scheme 151) includes a step of insertion of C=0 into a C—Pd palladium-catalyzed reactions leading to the formation of pyranones (see Scheme 152)228 and piperidones (see Scheme 139 in Section V,A,2).211 It is useful to note that the 2,5-divinyltetrahydropyran derivative can be transformed catalytically by ruthenium trichloride into synthetically useful 3,4-dihydro-2//-pyran derivatives (Scheme 153).229... 

Pyrazolinones belong to the heterocyclic class of coupler and are widely used the sulfonamide (124) is representative of this type (51USP2537098). Substituted thiophenes (125) (58GEP1025265) and hydroxypyridones (126) (47USP2431190) are couplers which form blue-violet dyes resistant to light. Pyranones (127), analogous to the latter, have also been used (51USP2542849). 

Ketones derived from pyrans are called pyranones (also commonly pyrones), and the parent compounds are pyran-2-one 17 and pyran-4-one 18. Trivial names are used for the related benzo analogs coumarin 19, isocoumarin 20, dihydrocoumarin 21, chromone 22, xanthone 23, and chromanone 24. 

No conclusive mechanisms mechanism can be adduced for the opposite prooxidative and antioxidative activities observed for the metal complexes of these furanones owing to the lack of both detailed structural and kinetic analyses. Whether the opposite results can be attributed to different experimental conditions is also moot. Nevertheless, it is reasonable to expect that the structures of metal-furanone complexes are similar to those of the analogous metal-pyranone complexes discussed in Section in.B.Ld. 

Several naturally-occurring pyranone-based polypropionates have been synthesised from pyran-4-ones <05CC1687, 05OL641, 05OL819, 05OL2837> and an enantiopure cyclohexadiene-fused pyran-4-one analogous to one of these has been synthesised <050L407>. An enantioselective synthesis of (-t-)-candelalide has been described... 

The installation of amino-functional groups, in practice, was most easily accomplished at the C-4 position (Scheme 1.9). For instance, the a-D-pyranone ring on methymycin analog 45 could be converted into a 4-aminosugar 41 with a-o-rhodino-stereochemistry in four steps, via a reduction, activation of the resulting alcohol, azide inversion, and reduction strategy. Alternatively, this approach is... 

TMSK has also been employed in the synthesis of p5ra-nones via a [4 + 2] cycloaddition with an electron-rich 1,3-diene (eq 21). Alternatively, 2 equiv of TMSK can be used to react with an enamine to afford pyranones or the corresponding resorcinols. 1,3-Diaza-l,3-dienes have also been reacted with TMSK in an analogous way to furnish 4(3H)-pyrimidinones. ... 

The rhenium catalyst also allows the alkyne Insertion into acyclic ketoester 47, delivering 5-keto ester 48 and its isomers, based on the position and geometry of the alkene moiety (Scheme 6.9) [24]. The product mixture can be converted into a sole compound, 2-pyranone 49 by heating or treatment with tetrabutylam-monium fluoride (TBAF) via loss of EtOH. An analogous insertion into C-C=0 bonds of 1,3-dicarbonyls was reported to proceed without transition metal catalysts when an activated alkyne [25] or aryne [26] was used. 

As noted in Section 2.2, when an epoxycyclopentenone 7 was formed thermally, it largely isomerized into the isomeric pyranone 8 (Scheme 3 2000 TL9189). This is a general process and FVP of the benzo-, naphtho-, and benzofuro-cyclopentene epoxides 347, 349, and 351 leads to the isocou-marins 348, and analogs 350 and 352, the last of which is related to the natural product coriandrin (Scheme 68 2000TL3677). 

A good analogy for the proposed reaction of the endoperoxide (47) is the chemiluminescent thermolysis of the pyranone endoperoxide (52) in the presence of appropriate fluorescers [69, 70]. 

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