1.4- Thiazines spectra

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

Zerner s intermediate neglect of differential overlap (ZINDO)/PM3 calculations of thiazinylium compound 35 were compared to its ultraviolet/visible (UVA is) absorption spectrum (Figure 3) <2000JOC6388>. The authors attribute the observed 453 and 403 nm bands (calculated to be at 456 and 412 nm) to highest occupied molecular orbital (HOMO)-LUMO and HOMO-LUMO + 1 transitions of the 1,2-thiazine sulfonium imide. 

Fully conjugated thiazine 46 has only one hydrogen (C-8) in the 1,2-thiazine ring which is observed at 8.59 ppm, while the resonance of the attached carbon atom occurs at 141.4 ppm in the NMR spectrum (Figure 13) <2005JOC9314>. 

Three absorption bands are found in the UV spectra of 6//-l,3-thiazine-6-thiones 33 and 34. The spectrum of the 2-phenyl derivative contains bands at A ax = 253, 314, and 425 nm. A blue shift is seen when the 2-phenyl substituent is replaced by the dimethylamino group and the bands are observed at Aniax= 240.5, 288, and 428 nm <1997S573>. 

Classes Of Sensitization, a. Photoreducible Dye Sensitization. In 1954 Oster (7) reported the first documentation of a dye-sensitized photoredox system. During the course of his work, Oster identified several classes of effective dyes, termed by him "photoreducible." These included examples of the classes of acridine, xanthine, and thiazine dyes. Figure 3 illustrates an example of each class, chosen in such a manner that the entire visible spectrum is covered by their absorption spectra. In Oster s work, identification of suitable activators (reduc-tants) to use in conjunction with the dyes was empirically determined. 

In the case of thiazine-4,6-diones, in contrast to the spectrum of the unsubstituted compound 92 (C=0,1640 cm ), there are three absorption bands. One is at 1640 cm-1, corresponding to the enol form, and two are at 1690 and 1730 cm"1, corresponding to the diketo form. In this example, the H-NMR spectrum suggests the presence of three tautomeric forms 93,94 and 95. In conclusion, we record a few absorptions bands for two thiazine-2-thiones (96) [82JCS(P1)2149]. 

The described synthesis of l,4-thiazino[3,2-6][l,4]thiazine (305) <87JA4308> starts with the reaction of aqueous glyoxal (302) with iV-methylguanidinium chloride (303) in water (pH 8). The resulting 2-amino-4,5-dihydro-4,5-dihydroxy-l-methylimidazolium chloride (304) is treated with 2-amino-ethane thiol in H20 (pH 8-9) to give either (305) or (306). The NMR spectrum of the product supports both of the structures (305) and (306) there is only one diastereomer <87JA4308>. 

The 13C NMR spectrum of the condensation product of thiazolium AT-ylide (194) with DMAD provided definitive evidence in support of the pyrrolo[2,l-c][l,4]thiazine (196) structure. Particularly important is the absence of an absorption that could be assigned to the tertiary C-5 in (195), this absorption being anticipated at 565.5 (76JOC187). 

Heinecken et found that a series of quinoneiminoid pheno-thiazine dyes, like methylene blue and its analogs, give ESR signals in sulfuric acid, the four lines of which have relative intensities 1 2 2 1. In alkaline solutions the spectrum consists of a 1 1 1 triplet. In both cases high resolutions were achieved with solutions in... 

Shine and Mach (1965) have reported the spectrum of the pheno-thiazine radical-cation (45), generated by treatment with sulphuric acid of either the parent compound or its neutral radical (i.e. the conjugate base) on treatment with water. Radical-cations of related heterocycles have been studied using similar methods (Shine and Small, 1965 Shine and Davies, 1965). 

The protons at position 2 of 2-unsubstituted 2//-l,4-thiazines resonate in the 5 136-3.40 region. " The chemical shift of the 3-proton of a 3-unsubstituted 2//-l,4-thiazine has not been reported, and the only example of a 5-unsubstituted 2ff-l,4-thiazine whose NMR spectrum is available is compound 19 its 5-proton absorbs at 5 8.43. The 6-protons of 3,5-diaryl-2//-l,4-thiazines appear in the S 6.30-6.53 region - a slight deshielding of the 6-proton (to S 6.13) is observed in the case of the bis(thiazine) 24. 

The protons at positions 2 and 6 of symmetrical thiazine dioxides resonate in the 5 5.95-6.36 region in the case of the anion 48, the protons are shifted upheld by 0.45 ppm (to 5 5.91). The parent compound 40 provides the only example of a 4H-l,4-thiazine dioxide, unsubstituted at positions 3 and 5, whose NMR spectrum has been reported the 3- and 5-protons appear as a multiplet centered at S 1.06f ... 

Dihydro-2f/-l,4-thiazines should absorb weakly owing to the n- n transitions of the C=N group. The only reported UV spectrum is that of 87, which absorps at 269 nm (e 105). ... 

Numerous spectra recorded for 1,2-benzothiazines include the 13CNMR of piroxicam (29),78 the electron spin resonance spectrum of the paramagnetic semidione obtained from base/oxygen oxidation of 3,4-dihydro-1,2-benzo-thiazin-4(2H)-one 1,1-dioxide 10,79 and the mass spectral fragmentations of 4-hydroxy-1,2-benzothiazines described in detail by Rasmussen8 and by Heyes et al.i0 The infrared, ultraviolet, and nuclear magnetic resonance spectra of various 1,2-benzothiazines are reported.4,6 8-10 17,21 34 66 Representative spectral data of 1,2-benzothiazines are presented in Table I. 

S) and its trans- and ciy-4a,7-H-7-ethyl derivatives indicated that trans-4a,7-H-7-ethylperhydropyrido[l,2-c][l,3]thiazine and the ds-4a,7-H-7-ethyl analog exist exclusively in the rrans-fused and the S-inside cis-fused conformation, respectively, containing the ethyl group in the equatorial positions, whereas the parent perhydropyrido[l,2-c][l,3]thiazine in CDCI3 at 25°C is a ca. 25 75 mixture of the S-inside c/s-fused and tra/u-fused conformations. At -75°C, where the interconversion is slow in a 1 1 mixture of CS2 and THF-dg, the signals of both conformers of perhydropyrido[l,2-c][l,3] thiazine can be detected. The NMR spectrum shows the presence of 64% of the frans-fused and 36% of the S-inside cis-fused conformer [82OMR(20)239]. 

Thiazin-4-ones (8) bearing alkyl groups at C-2 exhibit two bands in their UV spectra at 2max = 233-258 nm and 278-298 nm. This is altered if an electron-donating group is present at C-2 and, for example, a bathochromic shift of about 30 nm is observed in the spectrum of 2-(N,N-dimethylamino)-6-phenyl-1,3-thiazin-4-one (9). 

The pyrimido[2,1 -b][ 1,3]thiazine-diones (369)-(372) can be described only by a series of mesomeric forms. For (370) <77ZN(B)1204> and (369) <74ZN(B)258> the IR spectrum supports the mesoionic enolate/enol forms. Compounds (371) have poor stability, (371 R = H) decomposes above its melting point with the expulsion of C3O2 in water or alcohols it undergoes ring fission to malonic acid/esters (72S312). 

Sensitization of photogalvanic action by dyes which are themselves not capable of photoredox action has been demonstrated (7). Action spectra of solutions containing rhodamine 6G and two coumarin dyes in addition to thionine and methylene blue closely parallel absorption spectra, corresponding to the possible use of about 50% of the insolation spectrum and a theoretical maximum sunlight engineering efBciency of 7 %. It has been demonstrated that rhodamine 6G does, in fact, increase the power output of iron-thionine (or other thiazine) cells under white-light illumination an approximately 40% increase has been observed under illumination with 35 mWcm" (8). 

Spectrophotometric detection based on the methylene blue (MB) method is the approach most commonly adopted for online derivatization and determination of sulfide in water due to its inherent selectivity. The so-called Fischer s reaction involves oxidative coupling of A, iV-dimethyl-p-phenylenediamine (DMPD) with sulfide ions in the presence of an oxidizing reagent (namely, Fe(III)) in acidic medium, thus rendering a heterocyclic thiazine dye, the MB. Different flow techniques described in the literature, such as FIA, SIA [11,12], and multisyringe flow injection analysis (MSFIA) [13-17] have exploited this reaction, covering a broad spectrum of possibilities with respect to analytical features. 

Copp and coworkers [78] reported the isolation of a pair of thiazine-containing quinolindione alkaloids from the New Zealand ascidian Aplidium sp. The HMBC spectrum optimized for 6 Hz afforded... 

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