Thiopyrans structure

Table 2 Benzo Fused Thiopyrans Structure and Nomenclature...

Adducts of type (39 X = CO-Ph or C02Me), containing the AH-thiopyran structure, are formed from l,2-dithiole-3-thiones and acetylenes ... 

The formation of 2-(t-butyl)-2-trimethylsilyl-2//-thiopyran has recently been reported from 1-substituted 1,3-butadienes with /-BuCSSiMe3 (92MI1) (see Scheme 2). An unusual product with proposed structure 47b has been reported (84JOC5143) from benzothiopyrone 46 on reaction with sec-butyl lithium (46 - 47a — 47b, Scheme 3) on the basis of spectroscopic data. 6-Methylthio-2//-thiopyran was isolated after the flash vacuum thermolysis of more complex starting precursors (93TL2605). 

Crystal and molecular structures of 2,4,4,6-tetraphenyl-4//-thiopyran-1-oxide (143) and the corresponding 1,1-dioxide 141a were investigated to show the boat conformations of the heterocycles as well as an interesting... 

Structural determination of dipyrazolo[4,5-A5, 4 -z] thiopyrans by nOe measurements has been described in CHEC-II(1996) < 1995CHEC-II(8)967>. 

In this section, compounds are described that differ from 6 by the replacement of one or more methylene groups by heteroatoms or heteroatom groups. Quantum-chemical calculations on such species have not been carried out. However, on the basis of the results discussed in the above sections and depicted in Schemes 6.42 and 6.64, there is no doubt that all reactive intermediates under consideration are genuine allenes. After all, the tether across the allene subunit is larger in the corresponding compounds in this section than in 3<52-lH-pyridine (179), 3<52-pyran (180) and 3<52-thiopyran (299) owing to the absence of a double bond. Thus, compared with these models, the allene structures in this section suffer from less strain and are hence stabilized relative to their zwitterionic states. 

The yields of the isolated products are summarized in Table 7 and their structures are shown in Figure 9. The mechanism of formation of the fused system 98, which involves a thiophene-thiopyran ring enlargement, is discussed <2004TL2189>. 

Limited knowledge exists with respect to detailed molecular structures of simple pyrans and heteropyrans. The semiempirical CNDO/2 calculations, using a full geometry optimization procedure, predict 4 and 5 to exhibit small deviations of the heterocyclic rings from the planar conformations.34 Unfortunately, similar calculated data for thiopyrans 6, 7, and 9 were not presented.45 Accounts of several X-ray diffraction investigations on compounds possessing pyran or thiopyran fragments are available.46 51... 

A report on the Friedel-Crafts acetylation of 3-methyl-4//-thiopyran (3)4 should be considered with caution because of lack of a sufficient structure proof for 3. 

I3C-NMR spectra of the series of substituted 2//-thiopyrans 111 and 114 reveal a very good linear correlation between the l3C chemical shifts of 631 and 13C or 15N chemical shifts of analogous thiazines 632, suggesting a high degree of structural similarity between both series.463... 

Molecular refraction was used in a consideration of a 2//-pyran structure.475 Occasionally, liquid pyrans and thiopyrans have been characterized by refraction indices.19 24 144 189 238 314 427... 

Table 11 X-Ray Crystallographic Structure Data for 4-Acetyl-1,3-dimethyl-1//-thiopyran 1-Oxide (78CC197)...

Enaminothiones and related structures and their cyclization reactions with alkenes have been discussed in Section 2.25.4.2.1, where the preparation of dihydro systems was described. Under appropriate conditions, elimination of the amino substituent may be induced with the production of a thiopyran system (equation 103) (75T3059), though in some cases in which an alternative leaving group is present the amine jnav be retained... 

Figure 5 shows the molecular structures of rfs-2-nitro-7-(dimethylamino-)-9-(2,3,-dihydro-l J-f-naphtho[2,l-b]thiopyran-l -ylidene)-9J-f-thioxanthene ((P)-cis-17) and trans-dimethyl-[l-(2-nitro-thioxanthen-9-ylidene)-2,3-dihydro-lJ-f-ben-zo[f]thiochromen-8-yl]amine ((P)-trans-18). Anti-folded helical structures, in which the top and bottom parts are respectively tilted up and down relative to the plane of the central olefmic bond, are clearly observed. The extent of folding and twisting in these and related overcrowded alkenes can vary considerably. It should be emphasized that only minor deviation from planarity occurs at the central double bond (dihedral angles 5.4° (17) and 6.8° (18)), while normal bond lengths are found (1.353 A (17) and 1.338 A (18)).130,311... 

The intermolecular Diels-Alder reactions of 1,3-dithioles (163) with DMAD and DEAD produced the first 7//-thieno[2,3-c]thiopyran-7-thiones (164) and 47/-thieno [3.2-c]thiopyran-4-thiones (165), the structures of which were confirmed by X-ray diffraction. Further work on the mechanism of the cycloaddition and subsequent rearrangement is in progress (Scheme 46).191... 

---