27/-Thiopyrane

The equilibria between 27/-thiopyrans 63 (R = 4-MeOC6H4 R = Ph, 4-MeOC6H4) and their corresponding thiopyrylium salts were utilized to replace CI04, BF4-, Cl-, and CF3C02" ions by other counterions in the patent literature (88URP1447824). 

Methyl-27/-thiopyran was identified among 20 other components in the oil from Allium sativum (88MI3). The supplementation of boiler chick feeds with various selenium compounds including 4//-selenopyran 13b has been investigated (90MI1). 

Introduction of trimethylsilyl substituents attached directly to the ot-carbon atom of a-(benzotriazol-l-yl)alkyl thioethers provide new opportunities. Thus, treatment of lithiated monosubstituted a-(benzotriazol-l-yl)alkyl thioethers with chlorotrimethylsilane produces a-(trimethylsilyl)alkyl thioethers 837. In reactions with hexamethyl-disilathiane and cobalt dichloride, thioethers 837 are converted to thioacylsilanes 838 that can be trapped in a Diels-Alder reaction with 2,3-dimethylbutadiene to form 2-alkyl-4,5-dimethyl-2-trimethylsilyl-3,6-dihydro-27/-thiopyrans 839 (Scheme 133) <2000JOC9206>. 

The relative trans stereochemistry of the substituents in the tetrasubstituted 3,4-dihydro-27/-thiopyran 85, an intermediate isolated from the [4+2] cycloaddition between an enaminothione and a nitroalkene, has been established by H NMR spectroscopy <1994JPR434>. The methylene units of 5-(diethylphosphono)-3,4-dihydro-277-thiopyran 86 appear as multiplets in the range 2.0-2.8 ppm and the vinyl proton (H-6) displays coupling to the P atom with V= 21.6Hz <20050BC924>. 

The 13C NMR spectra (THF-. The following features are noteworthy from a comparison of their 13C NMR spectra. The chemical shift of C-4 has decreased by ca. 36 ppm which is indicative of an increase in charge density and Vqh for C-6 has increased by ca. 36 Hz which is suggestive of sp2 hybrid character for C-6 both features support a delocalized allylic anion. 

Benzyl-2,4,6-triphenyl-27/-thiopyran 236 shows two absorption peaks in the UV which are only marginally influenced by the polarity of the solvent, typical of jt,7t transitions, and which are in general agreement with those calculated using INDO/1-C1 for geometry optimized at the MNDO level (Table 11a). 

Treatment of 3,6-dihydro-27/-thiopyrans with iVuodosuccinimide in the presence of a carboxylic acid results in ring contraction to a ir-4-iodo-5-carboxymethylthiolane. An iodonium ion is considered to be the initial product from which a bicyclic thiiranium species is generated which is attacked by carboxylate ion (Scheme 31) <2004EJ074>. 

Thiopyran-2-thione 334, derived from tetrathiafulvalene by loss of CS2, undergoes a [2+2] cycloaddition with the fullerene C60F18 involving the more electron rich 5,6-double bond (Equation 63) <2003CEJ2008>. 

Further examples of the photolytic generation of thioaldehydes from phenacyl sulfides include the synthesis of 3,6-dihydro-27/-thiopyrans bearing a variety of functions at C-2 of which some are potent acyl-CoA-cholesterol acyl-transferase inhibitors (Equation 135) <1996BMC1493>. 

Doubly activated methylene compounds react with thionyl chloride in the presence of triethylamine to generate sulfines which can be trapped by 1,3-dienes to give 3,6-dihydro-27/-thiopyran 1-oxides 446. Facile deoxygenation makes this an attractive route to 2,2-disubstituted 3,6-dihydrothiopyrans (Scheme 151) <1999PS(153)119, 2004EJ074>. 

An optimized inexpensive synthesis of tetrahydrothiopyran 4-one which lends itself to scale-up involves a Dieckmann cyclization of dimethyl 3,3 -thiobispropanoate <2007S1584>. Efficient conversions to 3,6-dihydro 4-trimethylsilyloxy-27/-thiopyran <2007S1584>, the corresponding 4-vinylstannane <2007JOC1507> and the 4-oxo-tetrahydro-27/-thiopyran-3-yl A-methyl-iV-phenylcarbamate <2007SL293> have been accomplished. 

Aroyl-27/-thiopyrans are alkylated at sulfur to give 1-alkylthiopyranium salts, deprotonation of which affords the stable, dark-red thiabenzenes 479, a reaction which can be reversed by treatment with HBF4 (Scheme 71) <2001J (Pl)2269>. 

Note 5. At room temperature the 3,3-sigmatropic rearrangement begins. The anmonia, still present during the work up, will cause ring closure of the allenic dithioester to a 2-ff-thiopyran derivative. 

Hydroxy-THISs add to the C-C bond of diphenylcyclopropenethione (181. Inner salts without substituents in 5-posnion react similarly with diphenylcyclopropenone (Scheme 10) (4, 18). Pwolysis of the stable adducts (9) leads to rupture of the R-C-CY bond. Subsequent ring closure yields 10. When Y = O. 10 eliminates COS. producing 2-pyridone. When Y = S. 10 is isolated together with its isocyanate extrusion product, a thiopyran-2-thione (18). 

Thiopurinols applications, 5, 343 synthesis, 5, 319 tautomerism, 5, 308 Thiopyrans — see Thiins... 

Thiopyran and thiopyrylium salts synthesis and properties 98MI18. 

No tautomeric interconversions have been observed between 4//-pyrans (1, X = O) and 2//-pyrans (2, X = O), 4//-thiopyrans (1, X = S) and 2H-thiopyrans (2, X = S), or their benzo-fused derivatives. Under normal conditions, all these compounds exist as sole isomers that are initially formed, both in solution and in the solid state. The only tautomeric equilibrium reported was that between the two possible 2H isomers of the unsymmetrical sulfone 3 (77TL1149). 

Electroreductions of 2//-thiopyrans 13a and 13b each afforded an equimolar mixture of isomeric dihydrothiopyrans 14a and 14b (Scheme 4) (97MI2). Although the products were not separated, no 13a 13b or 14a 14b interconversion was... 

The relative stability of lithiated thiopyrans seems to depend upon the heterocyclic ring substitution. Thus, a-lithiated 2,6-diphenyl-2//-thiopyran 16 rearranges into the y-lithiated derivative 17 (Scheme 5) (82JOC680), while the reverse transformation occurs on lithiation of 2,6-diphenyl-4-diethylphosphonylthiopyran (80JOC2453). 

Thiopyrans formed on irradiation of the corresponding 4H derivatives are less prone to ring opening than 2//-pyrans. This led to the study of the photochemistry of variously substituted 4//-thiopyrans. Irradiation of 3,5-unsubstituted... 

The mechanism suggested earlier for the similar isomerization 34 35 involving the reaction of a 1,2-dihydroquinoline molecule with the starting quinolinium salt 33 (Scheme 11) is analogous to that of 4//-thiopyran isomerization discussed above (cf. Scheme 3) and is supported by deuterated substrate studies (85CJC412). Further support for this mechanism is the absence of such isomerization for 4-substituted derivatives such as 1,4-dimethyl-1,2-dihydroquinoline [94JCS(CC)287]. 

By Acid-Catalyzed Ring Enlargement of Benzo A cyck>propa e]thiopyrans... 

Halo-l-benzothiepins 4 can be synthesized by the treatment of 7a-halobenzo[fe]cyclopropa-[e]thiopyran-7-ols 2 with hydrogen bromide and subsequent hydrogen bromide elimination from the 2,4-dihalo-2,3-dihydro-l-benzothiepins 3 by l,5-diazabicyclo[4.3.0]non-5-ene (DBN).9 The alcohols 2 are prepared by Grignard reaction of the corresponding 7a-halobenzo[ft]cyclopropa[c]thiopyran-7-ones l18 and are used for the synthesis without purification. The intermediate dihalodihydro-l-benzothiepins 3 are not isolated due to their thermal lability related and more stable compounds are described in Section 2.1.2.1. 

By Elimination with Concerted Ring Expansion from Benzo[6]cyclopropa[r/]thiopyrans... 

Treatment of 2,7-di-/ert-butylthiepin (1) either directly with bromine at — 78 °C, or with pyridinium bromide perbromide at room temperature, gives the thiophene compound 2. In contrast, bromination with bromine-1,4-dioxane complex or pyridinium bromide perbromide in the presence of acetic acid leads to the thiopyran derivative 3.87 To account for these results a homothiopyrylium ion has been proposed as a common intermediate, formed by electrophilic bromination at C4 in the first step. 

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