HETEROCYCLES

Paper | Special issue | Vol. 80, No. 2, 2010, pp. 1339-1352
Received, 4th September, 2009, Accepted, 13th October, 2009, Published online, 14th October, 2009.
DOI: 10.3987/COM-09-S(S)124

■ 2-Substituted Isotellurochromenium Salt Derivatives: Preparations, Structures, Spectroscopic Properties

Haruki Sashida,* Shoko Nakabayashi, Mamoru Kaname, and Mao Minoura

Faculty of Pharmaceutical Sciences, Hokuriku University, 3-Ho, Kanagawa machi, Kanazawa 920-1181, Japan

Abstract

Several types of novel isotellurochromenium salt derivatives (2-10) were prepared from the isotellurochromenes (1). The isotellurochromenium tetrafluoroborates (2), triflates (3-5), tosylates (6) and mesylates (7) are telluronium salts, and the dihalogenoisotellurochromenes (8-10) are telluranes. The molecular structures of the isotellurochromenium tosylate (6a) and the dichloroisotellurochromene (8a) were characterized by an X-ray crystallographic analysis using the 3-tert-butyl derivatives.

INTRODUCTION
The chemistry of the telluronium salts has recently been developed in connection with that of hypervalent organotellurium compounds.2 Generally, stable telluranes (tetravalent tellurium compounds),3, 4 such as telluium tetrahalides, dialkyltelluride dihalides and tetraaryltelluranes, have a trigonal bipyramidal center on the tellurium cation and the tellurium-carbon bonds are composed three sp2 and two p-orbitals, while the tellurium center of a telluronium salt3, 4 has a tetrahedral and three equal sp3 bonds. Various bivalent six-membered tellurium-containing mono-cyclic heterocycles, i.e., tetrahydropyrans, 2H-telluropyrans, 4H-telluropyrans, 4H-telluropyran-4-ones, and benzene-ring fused compounds, i.e., benzo tetrahydropyrans, 2H-tellurochromenes, 4H-tellurochromenes, 2H-tellurochromen-2-ones, 4H-tellurochromen-4-ones, and 1H-tellurochromen-1-ones have already been prepared,5-7 and the structures of some have been unequivocally assigned based on single-crystal X-ray crystallographic analyses and NMR studies. Their basic and only limited reactivities, such as halogenation, alkylation and allylation, on the tellurium atom have been examined. Only NMR studies of the isoselenochromanes, relative six-membered selenium analogues have been reported by Hori and Kataoka et al.8
Previously, we succeeded in the synthesis of the novel isotellurochromenes (1), which are the six-membered tellurium heterocycles, and the transformation into the 2-benzotelluropyrylium salts,9 six-membered aromatic heterocycles containing a tellurium cation. The 2-benzotelluropyrylium salts reacted with several nucleophiles,10 such as alcohols, amines, the cyanide ion, a carbonyl compound (acetone), Grignard reagents, organocopper reagents11 and allyltributyltin,12 to give many 1-substituted isotellurochromenes. In addition, we reported that (E)-o-(2’-lithiovinyl)benzyllithium,13 generated by the reaction of the isotellurochromenes 1 with BuLi, was useful as a 1,5-dilithiated synthetic building block. However, the simple reactivity has not yet been examined for the isotellurochromenes. In this paper, we report the preparation of the various types of isotellurochomenium salt derivatives by the alkylation, arylation and halogenation of the isotellurochromenes (1), and their spectroscopic properties including X-ray analyses.

RESULTS AND DISCUSSION
1. Preparation of isotellurochromenium salts
Several types of isotellurochromenium salts and related compounds (2-7) were newly prepared from the isotellurochromenes (1) as shown in Scheme 1. The reaction of the isotellurochromenes 1 with methyl iodide and 1.1 equiv. of silver tetrafluoroborate (AgBF4) in CH2Cl2 at room temperature gave the 2-methylisotellurochromenium tetrafluoroborates (2a, 2b) in 84 and 75% yields, respectively. The treatment of the isotellurochromenes (1) with methyl trifluoromethanesulfonate (triflate, OTf−) or ethoxycarbonylmethyl triflate14 in acetonitrile at 0 °C similarly afforded the corresponding triflates 3a, 3b, 4a, 4b in high yields. 2-Phenylisotellurochromenium salt (5) was also synthesized from the isotellurochromene (1). The phenylation reaction of 1 was conducted using the diphenyliodonium triflate and copper (II) diacetate.15 Heating at 140 °C of a mixture of 3-tert-butylisotellurochromene (1a), diphenyliodonium triflate and a catalytic amount of copper (II) diacetate produced 2-phenylisotellurochromenium triflate (5a) in 75% yield. However, the reaction of 3-unsubstituted isochromene (1b) under the same conditions gave a complex mixture; no 2-phenylisotellurochromenium triflate (5b) was produced. When the 3-alkylisotellurochlomenes were phenylated with the same reagents, no 2-phenylchromenium salts were obtained. The 2-methylisotellurochromenium sulfonates (6a, 6b) were produced by the heating of 1a, b and methyl p-toluenesulfonate (methyl tosylate, MeOTs) at 60 °C under solvent free-conditions in 98 and 57% yields, respectively. Methyl methanesulfonate (methyl mesylate, MeOMs) also reacted with 1 to give the mesylates (7a, 7b) in a similar manner.

2. Preparation of 2,2-dihalogenoisotellurochromenes
The treatment of the isoselenochromene with sulfuryl chloride is known16 to give the 2-benzoselenopyrylium chloride via the unstable dehydrochlorination of the dichloro-adduct. In contrast, both the cyclic and acyclic tellurides react with sulfuryl chloride to afford the essential corresponding dichlorotellurides, which were stable enough to be isolated. Therefore, the chlorination of the isotellurochromenes 1 using sulfuryl chloride was carried out. The reaction of 3-tert-butylisotellurochromene (1a) with a small excess of sulfuryl chloride in hexane at 0 ˚C produced 2,2-dichloro-3-tert-butylisotellurochromene (8a) in almost quantitative yields as stable prisms. 2,2-Dibromo-3-tert-butylisotellurochromene (9a) and 2,2-diiodo-3-tert-butylisotellurochromene (10a) were also prepared by the reaction of the 3-tert-butylisotellurochromenes (1a) with bromine and iodine, respectively. 3-Unsubstituted dihalogenoisotellurochromenes (8-10b) were also obtained under similar conditions in good yields. The obtained compounds 2-10 in this way were thermally and photochemically quite stable crystals except 4b. The results of these derivatives 2-10 are listed in Table 1.

Next, we examined some reactions of the halogenoisochromenes (8-10). The dichloroisotellurochromenes (8a, b) were quantitatively dechlorinated under treatment with sodium sulfide in hexane at room temperature reverting to the isotellurochromenes (1a, b). A similar dehalogenation of the dibromo 9a, b and diiodo derivatives 10a, b also smoothly proceeded to afford 1a, b. The treatment of 8a with NaOMe in MeOH gave the 1-methoxyisotellurochromene (11) in 98% yield. This reaction would proceed via the intermediates, telluropyrylium chloride (12) or 1-chloroisotellurochromene (13), generated by the dehydrochlorination from 8a, following by the nucleophilic attacking of the methoxide ion at the C-1 position affording the 1-methoxyisotellurochromene (11). The 1-methoxyisochromene (11) was also obtained from the dibromo (9a) and diiodoisochromemes (10a) in high yields. When 8a and 9a were treated with diethylamine in benzene at 50 ˚C, the reaction mixtures immediately became yellow, and the starting materials disappeared. The 1-(diethylamino)isotellurochromene (14) was obtained in high yields. However, 14 was not obtained from 10a. Compounds 11 and 14 were identical to the authentic samples, which were previously prepared by the reaction of the 2-benzotelluropyrylium salt with NaOMe or diethylamine.

2. 3. Structures of isotellurochromenium salts
The structures of these telluronium salts (2-7) were mainly characterized on the basis of their 1H-NMR, MS and elemental analyses. Their 1H-NMR data are listed in Table 2. The MS spectra of the isotelluronium tetrafluoroborates (2) and triflates (3-5) did not display any molecular ion peaks (M+), but showed only fragment ion peaks arising from the cationic isochromenium moieties. Two 1-benzylic proton signals of 2-5 appeared as a pair of doublets (coupling constant, J = 14 Hz) at δ ca. 4.0-4.9 in the 1H-NMR spectra (in CDCl3). Similarly, the MS spectra of the tosylates (6) and the mesylates (7) did not show the M+, and the 1H-NMR spectra (in CDCl3) of 6 and 7 had a pair of doublets at δ ca. 4.0-4.8 assigned to 1-benzylic protons with geminal coupling (J = 14 Hz). Similar 1H-NMR spectral data in CD3CN were also obtained. In all cases, the olefinic protons at the C-4 are observed as a singlet at 6.6-6.8. These spectral data suggest that the tetrafluoroborates (2), triflates (3-5), tosylates (6) and mesylates (7) are salts containing a tellurium cation.

On the other hand, the spectroscopic properties of the isoselenochromanium salts, six-membered selenium-containing heterocycles, have been reported by Hori and Kataoka et al.,8 but without X-ray analysis in 1990. They described that the tetrafluoroborate 15 and triflate 16 were selenium salts; their EI-MS did not show M+, but showed only fragment ion peaks arising from the cationic moieties. On the contrary, the MS spectra of the 2-methylisoselenochromanium tosylate (17) and mesylate (18) showed the M+. Hence, they concluded that the tosylate 17 and mesylate 18 had the selenurane structures with four covalent bonds. Therefore, an X-ray crystallographic analysis of the isotelluronium tosylates (6) was carried out in order to confirm the structure around the tellurium atom in this study. Fig. 2 shows the molecular structure of the 3-tert-butyl derivative (6a). Table 3 lists the selected interatomic distances, angles and torsional angles of 6a. For the crystallographic structure of 6a, the cationic tellurium containing a six-membered ring has twisted envelope skeletons. The bond lengths (Te-C, 2.122 and 2.144 Å) are slightly shorter than the observed value in the neutral telluracyclohexane skeletons (av. 2.157 Å) and this may be caused by the cationic attractive effect on the tellurium center, although the C-Te-C angle (89.8 °) in the heterocycle almost shows the expected value for the neutral telluracyclohexane skeletons (av. 89.3 °)17 The cationic tellurium center is weakly coordinated by the oxygen atoms in the counter anionic tosylate (2.815 and 2.944 Å), and such weak interactions or secondary bonds have been reported between the chalcogen onium and atoms in an anion in the solid state.18

4. Structures of the dihalogenoisotellurochromenes
The 1H-NMR data of the dihalogenoisotellurochromenes (8-10) are listed in Table 4. The M+ of the 2,2-dichloroisotellurochromenes (8) were observed in the EI-MS spectra, but very weak. The EI-MS of the 2,2-dibromoisotellurochromenes (9) did not show the M+, but showed a fragment ion peak assigned to M+-Br. Neither M+ nor M+-I of the 2,2-diiodoisotellurochromenes (10) were observed; only fragment ion peaks due to I2 from the M+. However, the elemental analyses of these dihalogenoisotellurochromenes (2-4) gave satisfactory results. The 1H-NMR spectra of 8-10 in CDCl3 showed two 1-benzylic proton signals as a singlet peak at δ 4.92–5.15. These findings suggest that the 2,2-dihalogenoisotellurochromenes 8-10 take the tellurane structures, which share the trigonal-bipyramidal geometry of the hypervalent tellulium compounds having two equal tellurium-halogen σ covalent bonds. The molecular structure of 8a was finally determined by X-ray crystallographic analysis (Fig. 3). Table 5 lists the selected interatomic distances, angles and torsional angles of 8a.

The tellurium containing six membered ring in 8a has an almost planar structure. The tellurium environment of 8a has a pseudo-trigonal bipyramidal (TBP) geometry consisting of two chlorine atoms in the apical positions and two equatorial carbon atoms. The bond angle of Cl-Te-Cl (171.9 °) indicates repulsions between the Te-Cl bonds and lone pair electrons on the Te atom. This bond angle and the bond lengths of Te-Cl (2.505 and 2.541 Å) are comparable to those observed in the R2TeIVCl2 compounds where the corresponding averaged bond angle and length are 174.9 ° and 2.508 Å, respectively.19

CONCLUSION
Several types of isotellurochromenium salts having a methyl, phenyl and ethoxycarbonyl group on the tellurium atom at the C-2 position, and the 2,2-dihalogenoisotellurochromenes were easily prepared from the parent isotellurochromenes in good to high yields in one-pot. BF4–, OTf–, OTs– and OMs– were selected as the counter anion of the salts. The 1H-NMR spectra of these derivatives were described and the X-ray crystallographic analyses were also reported. As a consequence, the 2-methylisotellurochromenium tosylate was found to have a telluronium salt structure with a tosylate as the counter anion.

EXPERIMENTAL
Melting points were measured on a Yanagimoto micro melting point hot stage apparatus and are uncorrected. IR spectra were determined with a Horiba FT-720 spectrometer. Mass spectra (MS) and HRMS were recorded on a JEOL JMS-DX300 instrument. NMR spectra were determined with a JEOL EX-90A (90 MHz) or a JEOL JNM-GSX 400 (400 MHz) spectrometer in CDCl3 or CD3CN using tetramethylsilane as internal standard and J values are given in Hz. Microanalyses were performed in the Microanalytical Laboratory in this Faculty.

Preparation of 2-methylisotellurochromenium tetrafluoroborate (2)
Silver tetrafluoroborate (220 mg, 1.1 mmol) was added to a mixture of isotellurochromene (1, 1.0 mmol) and MeI (1.0 mL) at 0 °C, and the mixture was stirred overnight at room temperature. Excess MeI was evaporated, the residue was triturated and extracted with MeCN, and filtrated to remove silver iodide. The filtrate was evaporated, and the residual solid was recrystallized from MeCN-Et2O to give 2.
3-tert-Butyl-2-methylisotellurochromenium Tetrafluoroborate (2a)
EIMS (relative intensity) m/z: 317 [(M-BF4)+, 17], 302 (100), 300 (92), 157 (100), 115 (48). IR (KBr) (cm-1): 1083 (BF4). Anal. Calcd for C14H19BF4Te: C, 41.86; H, 4.77. Found: C, 41.94; H, 4.57.
2-Methylisotellurochromenium Tetrafluoroborate (2b)
EIMS (relative intensity) m/z: 260 [(M-HBF4)+, 5], 246 (45), 244 (42), 115 (100). IR (KBr) (cm-1): 1097 (BF4). Anal. Calcd for C10H11BF4Te: C, 34.75; H, 3.21. Found: C, 34.64; H, 3.21.

Preparation of 2-methylisotellurochromenium triflate (3)
Methyl triflate (165 mg, 1.0 mmol) was added to isotellurochromene (1, 1.0 mmol) at 0 °C, and the mixture was stirred for 2-3 h at room temperature. The oily residue was washed with a mixture of Et2O and hexane (1:1), and the residual solid was recrystallized from MeCN-Et2O to give 3.
3-tert-Butyl-2-methylisotellurochromenium Triflate (3a)
EIMS (relative intensity) m/z: 317 [(M-OTf)+, 100], 315 (92), 302 (33), 157 (63). IR (KBr) (cm-1): 1161, 1248, 1281 (OTf). Anal. Calcd for C15H19O3F3STe: C, 38.83; H, 4.13. Found: C, 38.63; H, 4.01.
2-Methylisotellurochromenium Triflate (3b)
EIMS (relative intensity) m/z: 261 [(M-OTf)+, 38], 259 (30), 246 (35), 115 (100). IR (KBr) (cm-1): 1163, 1250, 1273 (OTf). Anal. Calcd for C11H11O3F3STe: C, 32.39; H, 2.72. Found: C, 32.38; H, 2.71.

Preparation of 2-(ethoxycarbonylmethyl)isotellurochromenium triflate (4)
Ethoxycarbonylmethyl triflate (295 mg, 1.25 mmol) was added to a solution of isotellurochromene (1, 1.0 mmol) in MeCN (5 mL) at 0 °C. The mixture was stirred overnight at room temperature and then evaporated. The oily residue was washed with hexane, and the residual solid was recrystallized from CH2Cl2-hexane to give 4.
3-tert-Butyl-2-(ethoxycarbonylmethyl)isotellurochromenium Triflate (4a)
EIMS (relative intensity) m/z: 302 [(M-OTf-CH2COOC2H5)+, 100], 157 (85). IR (KBr) (cm-1): 1724 (C=O), 1158, 1231, 1282 (OTf). Anal. Calcd for C18H23O5F3STe: C, 40.33; H, 4.32. Found: C, 40.39; H, 4.20.
2-(Ethoxycarbonylmethyl)isotellurochromenium Triflate (4b)
EIMS (relative intensity) m/z: 333 [(M-OTf)+, 35], 246 (37), 244 (35), 115 (100). IR (KBr) (cm-1): 1716 (C=O), 1169, 1250, 1277 (OTf). Anal. Calcd for C14H15O5F3STe: C, 35.04; H, 3.15. Found: C, 34.89; H, 2.99.

Preparation of 3-tert-butyl-2-phenylisotellurochromenium triflate (5a)
A mixture of isotellurochromene (1a, 302 mg, 1.0 mmol) and diphenyliodonium triflate (1.3 mmol) and copper (II) acetate (0.01 mmol) was heated with stirring at 140 ˚C for 3 h under argon atmosphere. The reaction mixture was cooled to room temperature and Et2O (50 mL) was added. The resulting crystals were triturated, collected by filtration, and washed with Et2O to remove iodobenzene and the by-products. The crude crystals were recrystallized from CHCl3- Et2O.
EIMS (relative intensity) m/z: 279 [(M-OTf)+, 100], 302 (12), 157 (71). IR (KBr) (cm-1): 1153, 1221, 1258, 1279 (OTf). Anal. Calcd for C20H21O3F3STe: C, 45.66; H, 4.02. Found: C, 45.44; H, 4.16.

Preparation of 2-methylisotellurochromenium tosylate (6)
A mixture of isotellurochromene (1, 1.0 mmol) and methyl p-tosylate (186 mg, 1.0 mmol) was heated at 60 °C under argon atmosphere with stirring for 2 h. After cooling, the solid was recrystallized from CH2Cl2-Et2O to give 6.
3-tert-Butyl-2-methylisotellurochromenium Tosylate (6a)
FABMS (relative intensity) m/z: 317 [(M-OTs)+, 100], 157 (45). IR (KBr) (cm-1): 1180, 1216 (SO3). Anal. Calcd for C21H26O3STe: C, 51.89; H, 5.39. Found: C, 51.71; H, 5.34.
2-Methylisotellurochromenium Tosylate (6b)
FABMS (relative intensity) m/z: 261 [(M-OTs)+, 100], 154 (85). IR (KBr) (cm-1): 1164, 1215 (SO3). Anal. Calcd for C17H18O3STe: C, 47.49; H, 4.22. Found: C, 47.37; H, 4.29.

Preparation of 2-methylisotellurochromenium mesylate (7)
A mixture of isotellurochromene (1, 1.0 mmol) and methyl mesylate (110 mg, 1.0 mmol) was heated at 60 °C under argon atmosphere with stirring for 2 h. After cooling, the solid was recrystallized from CH2Cl2-Et2O to give 7.
3-tert-Butyl-2-methylisotellurochromenium Mesylate (7a)
EIMS (relative intensity) m/z: 317 [(M-OMs)+, 10], 302 (100), 287 (28), 157 (100), 115 (48). IR (KBr) (cm-1): 1194, 1205 (SO3). Anal. Calcd for C15H22O3STe: C, 43.94; H, 5.41. Found: C, 44.03; H, 5.37.
2-Methyl-2-isotellurochromenium Mesylate (7b)
EIMS (relative intensity) m/z: 261 [(M-OMs)+, 5], 246 (55), 115 (100). IR (KBr) (cm-1): 1176, 1211 (SO3). Anal. Calcd for C11H14O3STe: C, 37.33; H, 3.99. Found: C, 37.12; H, 3.84.

Preparation of 2,2-dihalogenoisotellurochromene (8-10)
1.05 mol Equivalent amount of SO2Cl2 (142 mg), Br2 (170 mg) or I2 (267 mg) was added to a solution of isotellurochromene (1, 1.0 mmol) in hexane (20 mL) with stirring in an ice bath, and the mixture was stirred for 30 min at 0-5 °C. The resulting precipitate was collected by filtration, washed with hexane, and recrystallized from benzene-hexane to give 8-10.
3-tert-Butyl-2,2-dichloroisotellurochromene (8a)
EIMS (relative intensity) m/z: 376, 374, 372 (M+, 1, 3, 1), 337 (10), 302 (76), 300 (70), 157 (100). EIHRMS m/z: 371.9688 (Calc. for C13H1635Cl2130Te: 371.9672). Anal. Calcd for C13H16Cl2Te: C, 42.11; H, 4.35. Found: C, 42.26; H, 4.28.
2,2-Dichloroisotellurochromene (8b)
EIMS (relative intensity) m/z: 316 (M+, 1), 281 (6), 246 (36), 244 (34), 115 (100). EIHRMS m/z: 315.9059 (Calc. for C9H835Cl2130Te: 315.9065). Anal. Calcd for C9H8Cl2Te: C, 34.35; H, 2.56. Found: C, 34.30; H, 2.55.
3- 2,2-Dibromo- tert-butyl-isotellurochromene (9a)
EIMS (relative intensity) m/z: 381 [(M-Br) +, 76], 379 (59), 302 (100), 157 (84). EIHRMS m/z: 380.9488 (Calc. for C13H1679Br130Te: 380.9498). Anal. Calcd for C13H16Br2Te: C, 33.97; H, 3.51. Found: C, 34.01; H, 3.43.
2,2-Dibromoisotellurochromene (9b)
EIMS (relative intensity) m/z: 325 [(M-Br) +, 20], 246 (35), 244 (33), 115 (100). EIHRMS m/z: 324.8869 (Calc. for C9H879Br130Te: 324.8872). Anal. Calcd for C9H8Br2Te: C, 26.79; H, 2.00. Found: C, 26.89; H, 1.98.
3-tert-Butyl-2,2-diiodoisotellurochromene (10a)
EIMS (relative intensity) m/z: 302 [(M-I2) +, 55], 300 (51), 254 (100), 157 (54). EIHRMS m/z: 302.0301 (Calc. for C13H16130Te: 302.0314). Anal. Calcd for C13H16I2Te: C, 28.20; H, 2.91. Found: C, 28.03; H, 2.79.
2,2-Diiodoisotellurochromene (10b)
EIMS (relative intensity) m/z: 254 (I2, 100), 246 [(M-I2)+, 35), 115 (72). EIHRMS m/z: 245.9672 (Calc. for C9H8130Te: 245.9688). Anal. Calcd for C9H8I2Te: C, 21.72; H, 1.62. Found: C, 21.58; H, 1.58%.

X-Ray structure determination
Single crystals of 6a were obtained from solution of acetonitrile after slow evaporation of the solvent at room temperature, 8a from solutions of n-hexane/dichloromethane. Diffraction data were collected on a Bruker Apex-II CCD diffractometer equipped with a graphite monochromated MoKα radiation source (λ = 0.71073 Å). The structures were solved by direct methods (SHELXS-97),20 and refined by full-matrix least-square methods on F2 for all reflections (SHELXL-97)21 with all non-hydrogen atoms anisotropic and all hydrogen atoms isotropic.
For 6a, the structure analysis is based on 4449 observed reflections with I > 2.00 σ(I) and 240 variable parameters; colorless needles, 113 K, triclinic, space group P-1, a = 9.6655(2) Å, b = 10.5362(6) Å, c = 10.9056(1) Å, α = 80.724(7)°, β = 68.336(6)°, γ = 89.062(7)°, V = 1017.54(7) Å3, Z = 2, R = 0.0171, Rw = 0.0435GOF = 1.056.
For 8a, the structure analysis is based on 2822 observed reflections with I > 2.00 σ(I) and 163 variable parameters; yellow needles, 196 K, orthorhombic, space group Pbca, a = 8.3371(2) Å, b = 33.438(1) Å, c = 9.861(2) Å, V = 2758.79(12) Å3, Z = 8, R = 0.0324, Rw = 0.0959, GOF = 1.515.
CCDC-742488 for 6a and CCDC-742489 for 8a contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data request/cif.

Dehalogenation of 8-10 with Sodium Sulfide
General Procedure: A 2% aqueous Na2S solution (5 mL) was added to a solution of 8a (20 mg) in hexane with vigorous stirring in an ice bath. After stirring for 10 min, water (10 mL) was added to the reaction mixture, and the whole was extracted with CH2Cl2 (20 mL x 2). The combined extract was dried (MgSO4) and evaporated. The residue was chromatographed on silica gel using hexane-CH2Cl2 to give isotellurochromene (1).
From 8a: 98% yield. From 8b: 92% yield. From 9a: 97% yield. From 9b: 95% yield. From 10a: 98% yield. From 10b: 94% yield.

Reaction of 8-10a with NaOMe
28% NaOMe in MeOH (2 mL) was added to a solution of 8a (112 mg, 0.3 mmol) in MeOH (10 mL) at 0 °C. The reaction mixture was stirred for 15 min and then poured into ice-water. The aqueous mixture was extracted with CH2Cl2 (20 mL x 3), the organic layer was washed with brine (30 mL x 3) and dried over MgSO4. The solvent was evaporated to give the 1-methoxy-1H-isotellurochromene (11) in a nearly pure form as colorless oil. This compound was identical with an authentic sample in terms of 1H-NMR, IR and MS.
From 8a: 97% yield. From 9a: 97% yield. From 10a: 98% yield.

Reaction of 8-10a with NHEt2
Diethylamine (0.6 mL) was added slowly to a suspended mixture of 8a (112 mg, 0.3 mmol) in benzene (6 ml) at room temperature under argon atmosphere. The mixture was stirred at 50 ˚C for 1 h, and then extracted with benzene (20 mL x 3). Benzene layer was washed with brine (30 mL x 3) and dried (MgSO4), and evaporated to give the 1-diethylamino-1H-isotellurochromene (14) in a nearly pure form as colorless oil. This compound was also identical with an authentic sample in terms of 1H-NMR, IR and MS.
From 8a: 95% yield. From 9a: 93% yield.

ACKNOWLEDGEMENTS
This work was partially supported in part by a Grant-in Aid for Scientific Research from the Ministry of education, Science and Culture, Japan (19590022), and the Specific Research Fund of Hokuriku University (2008).

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19. Data of averaged bond length and angle were calculated based on the 57 examples of R2TeIVCl2 compounds using Cambridge Structural Database, CSD ver. 5.30., 2008: also see F. H. Allen, Acta Cryst., 2002, B58, 380.
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