4- Thio-4-pyrone

Electrophilic reagents become bonded to the carbonyl oxygen or sulfur atom of (thio)pyrones, leading to pyrylium salts. 

CuHi/V l-Thio-pyron-bis-loarbanaAiire. AtnytB8ter]-(33)-disiilfinaanre-(2.6) 18,566. 

Tetrahydro-1 -thio-pyron-dicarbon aaure.(3.5).di4thyleeter 18. 484. 

Dimethyl.4-thio-pyron (4)-dicarbon 8 iiFe>(3.5) di thylaBter 18, 495. 

Ci,HnC10 8 3.Chlor.2.6-diphenyH.thio-pyron.(4).S.dio yd 17 II410. 

The Chemical Abstracts nomenclature will be adopted, but when common trivial names are available, these will also be employed, e.g., 4-pyrone along with 4if-pyran-4-one. Unlike Chemical Abstracts, thio will be used to designate a thione and thia will imply a sulfur heteroatom. 

Except for several chapters in the comprehensive monograph on heterocyclic chemistry (84MI1) no special articles covering the recent past are available. This review is an attempt to discuss the literature up to Volume 117 (1992) covered by Chemical Abstracts together with some accessible papers published in 1993. Only isolable or spectroscopically identifiable thio-, seleno-, and teluropyrans without exocyclic double bonds (hetero-pyrones and heteropyranylidene derivatives) are considered. All benzo derivatives and their annulated heteroanalogs (spiroheteropyrans) are excluded. 

Mark6 and colleagues178 studied the Eu(hfc)3 catalyzed inverse electron demand Diels-Alder reactions between (—)-pantolactone derived chiral a-pyrones 279 and vinyl ethers and thio ethers 280. This auxiliary proved superior to other auxiliaries in these reactions. The reactions generally proceeded with high yields, affording the endo adducts 281 with de values generally above 95%. The de proved independent of the chirality or achirality of the Lewis acid employed, as (+)-Eu(hfc)3, (—)-Eu(hfc)3 and Eu(fod)3 all afforded the same diastereomer with >95% de (equation 78, Table 13). 

Thia-thio-y-pyrone 1,4 -Dithiopyrone 4 H-Thiopyran-4-thione... 

Thia-thio- a-pyrone 1,2-Dithiopyrone 2 H-Thiopyran- 2-thione... 

Ozonization of Thio-y-pyrones (6). Thio-y-pyrone and 2,6-dimeth dthio-y-py-rone react with ozone at a slower rate than the corresponding y-pyrones. The thio-y-pyrones take up 3 molecules of ozone. Not only do the C=C bonds react with ozone, but oxidation of the sulfur atom also occurs. When the reaction product of the ozonization is treated with dilute alkali and hydrogen peroxide, the solution contains alkali sulfate in an amount corresponding to the sulfur content of the thiopyrone. 

Difarom-2.6.diphenyl.l -thio-tetrabydro pyron-(4)-S-dioxyd vom Schmelzpviikt 234<> 17 n 303. 

A sulphur atom in the pyrone ring produces absorption at higher wavelength and greater intensity [63] the 4-thio analogue absorbs at even higher wavelength [63]. 

Chromone derivatives and their analogues 704 and 705 were used for synthesis of 4-fluoroalkylpyrimidines. In both cases, reaction with NCN binucleophiles was accompanied with recyclization of the y-(thia)pyrone ring to give (2-(thio) hydroxyphenyl)-substituted pyrimidines or their analogues (Table 37). 

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