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Synthesis 2009(10): 1739-1743  
DOI: 10.1055/s-0028-1088123
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© Georg Thieme Verlag Stuttgart ˙ New York

Convenient Methods for Synthesis of C 2-Symmetric Diphenyltetrahydro­thiophenes

Mariappan Periasamy*, Gurubrahamam Ramani, Gopal P. Muthukumaragopal
School of Chemistry, University of Hyderabad, Hyderabad, AP 500046, India
Fax: +91(40)23012460; e-Mail: mpsc@uohyd.ernet.in;

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Received 18 December 2008
Publication Date:
14 April 2009 (online)

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Convenient Methods for Synthesis of C2-Symmetric Diphenyltetrahydro­thiophenesSynthesis 2009; 2009(10): e2-e2
DOI: 10.1055/s-0029-1216797

Abstract

Racemic and optically pure (-)-(3R,4R)-3,4-diphenyltetrahydrothiophene, (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene, and (-)-(3S,6S)-3,6-diphenyl-1,2-dithiane were synthesized by use, in the crucial steps, of the easy-to-handle borane systems tetra­butylammonium borohydride-iodine and tetrabutylammonium borohydride-iodomethane.

Key words

diphenyltetrahydrothiophenes - 3,6-diphenyl-1,2-dithiane - asymmetric reduction - tetrabutylammonium borohydride - sulfur heterocycles

Chiral ligands containing sulfide moieties are useful for many asymmetric transformations, such as asymmetric epoxidations, [¹] catalytic asymmetric cyclopropanation of electron-deficient alkenes, [²] electrophilic sulfenylation of unsaturated carbon-carbon bonds, [³] and aziridination of N-electron-withdrawn imines. [4] They are useful for the synthesis of chiral alcohols and amines from organoboranes, [5] the synthesis of certain carbocycles [6] and functionalized N-heterocycles, [7] as well as the synthesis of biologically active molecules such as iso-agatharesinol, [8] swainsonine, [9] a side chain of Taxol, [¹0] and the anti-inflammatory agents [¹¹] neobenodine, cetirizine, and CDP-840. Previously, a simple protocol for accessing chiral C 2-symmetric 3,4-diphenylpyrrolidines via reduction of 2,3-diphenylsuccinic acid derivatives by use of the sodium borohydride-iodine reagent system was reported from this laboratory. [¹²] More recently, it was reported that the reagent systems tetrabutylammonium borohydride-iodine [¹³a] and tetrabutylammonium borohydride-iodomethane [¹³b] give better yields in borane reductions. Herein, we report simple, convenient methods for the preparation of both racemic and optically pure (-)-(3R,4R)-3,4-diphenyltetrahydrothiophene [(±)-1 and (-)-1], (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene [(+)-2], [¹4] and (-)-(3S,6S)-3,6-diphenyl-1,2-dithiane [(-)-3] (Figure 1) by use of these modified borane reagent systems in crucial steps in the synthesis.

(±)-3,4-Diphenyltetrahydrothiophene [(±)-1] is readily accessed by the synthetic protocol outlined in Scheme 1. Dimethyl (±)-2,3-diphenylsuccinate (5) is prepared in 80% yield from methyl phenylacetate in the presence of titanium(IV) chloride-triethylamine in dichloromethane at -45 ˚C. [¹5] Subsequent reduction of diester 5 by the easy-to-handle tetrabutylammonium borohydride-iodine or tetrabutylammonium borohydride-iodomethane system in anhydrous tetrahydrofuran provides (±)-2,3-diphenyl­butane-1,4-diol (6) in 75% or 74% yield, respectively. Further conversion into the corresponding ditosylate 7 by use of p-toluenesulfonyl chloride and pyridine followed by cyclization with sodium sulfide nonahydrate gives (±)-1 in 91% yield. [¹6]

Figure 1

Scheme 1 Synthesis of (±)-3,4-diphenyltetrahydrothiophene [(±)-1]

(-)-(3R,4R)-3,4-Diphenyltetrahydrothiophene [(-)-1] is readily prepared by a similar synthetic protocol starting from (R)-(+)-1,1′-binaphthalene-2,2′-diyl bis(phenylacetate) (9), which, in turn, is easily accessed by the reaction of phenylacetic acid with 1,1′-binaphthalene-2,2′-diol (8) (Scheme 2). Diester 9 is converted into the intramolecularly coupled diester (-)-(R,R,R)-10 in 80% yield in the presence of titanium(IV) chloride-triethylamine. [¹7] Subsequent reduction of 10 with tetrabutylammonium borohydride-iodine or tetrabutylammonium borohydride-iodomethane gives (-)-(2R,3R)-2,3-diphenylbutane-1,4-diol [(-)-6] in 71% or 75% yield, respectively. We observed that these reducing systems give better yields than the sodium borohydride-iodine system for the reduction of 10. Direct reduction of 10 to (-)-6 is necessary, since the hydrolysis of (-)-(R,R,R)-10 when potassium hydroxide in methanol is used leads to racemization of the resulting 2,3-diphenylsuccinic acid. Diol (-)-6 is tosylated with p-toluenesulfonyl chloride-pyridine to give (-)-7 in 84% yield; ditosylate (-)-7 is cyclized in the presence of sodium sulfide nonahydrate in refluxing ethanol to give (-)-(3R,4R)-3,4-diphenyltetrahydrothiophene [(-)-1] (91%). The structure of (-)-1 was further confirmed by X-ray crystal structure analysis. The ORTEP diagram is given in Figure 2.

Scheme 2 Synthesis of (-)-(3R,4R)-3,4-diphenyltetrahydrothiophene [(-)-1]

Figure 2 ORTEP representation of the crystal structure of (-)-1; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity

The chiral (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene [(+)-2] is synthesized by the protocol outlined in Scheme 3. (E)-1,4-Diphenylbut-2-ene-1,4-dione (11) is prepared in 74% yield by Friedel-Crafts acylation of benzene with fumaryl chloride. [¹8] Subsequent reduction of 11 with tin(II) chloride/hydrogen chloride in ethanol gives 1,4-diphenylbutane-1,4-dione (12) in 76% yield. [¹9] Diketone 12 is reduced with tetrabutylammonium borohydride-­iodine in the presence of a chiral oxazaborolidine system in anhydrous tetrahydrofuran to give (+)-(1R,4R)-1,4-diphenylbutane-1,4-diol (13) in 90% yield and 90% ee. We observed that in this case better yields are obtained when a smaller amount of tetrabutylammonium borohydride (0.8 equiv) is used compared to sodium borohydride (2.2 equiv). [¹³b,c] The nonracemic diol 13 (90% ee) was enriched by use of l-proline and boric acid to give (+)-(1R,4R)-diol 13 in 98% ee. [²0] The (+)-(1R,4R) diol 13 (98% ee) was mesylated with methanesulfonyl chloride-triethylamine in anhydrous dichloromethane to give (1R,4R)-1,4-bis(methanesulfonyloxy)-1,4-diphenylbutane (14) in 82% yield. [²¹] Finally, (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene [(+)-2] was obtained in 80% yield by the reaction of 14 with sodium sulfide nonahydrate in dimethyl sulfoxide. [¹4] Its structure was further confirmed by X-ray crystal structure analysis. The ORTEP diagram of (+)-2 is given in Figure 3.

Scheme 3 Synthesis of (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene [(+)-2] and (-)-(3S,6S)-3,6-diphenyl-1,2-dithiane [(-)-3]

Figure 3 ORTEP representation of the crystal of structure (+)-2; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity

Surprisingly, (-)-(3S,6S)-3,6-diphenyl-1,2-dithiane [(-)-3] was formed in 85% yield when the reaction of 14 with sodium sulfide nonahydrate was carried out in ethanol as solvent (Scheme 3). Such sulfur-sulfur-bond-containing compounds were previously reported to be obtained from the reaction of bromoisobutyrophenone and sodium sulfide in ethanol. [²²] Disulfides are useful synthons, as the sulfur-sulfur bond can be cleaved by numerous nucleophiles and electrophiles, and is also prone to oxidation. [²³] The structure of compound 3 was further confirmed by X-ray crystal structure analysis. The ORTEP diagram is given in Figure 4. [²4]

Figure 4 ORTEP representation of the crystal structure of (-)-3; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity

Since the chiral tetrahydrothiophene derivatives 1 and 2 and 1,2-dithiane 3 are readily prepared from simple and readily accessible reagents, the methods described here have considerable potential for further synthetic exploitation.

TiCl4 (Spectrochem, India) and (R)-(+)-1,1′-bi(2-naphthol) (Gerchem, Hyderabad) were used as obtained. CH2Cl2 was distilled over CaH2 and dried over 4-Å molecular sieves. THF was used freshly distilled over benzophenone/sodium. Melting points were determined on a Superfit capillary point apparatus and are uncorrected. IR (KBr) spectra were recorded on a Jasco FT-IR model 5300 spectrometer with polystyrene as reference. The ¹H (400 MHz) and ¹³C (100 MHz) NMR spectra of samples in CDCl3, with TMS as internal standard, were recorded on a Bruker Avance 400 spectrometer. Optical rotations were measured on an Autopol II automatic polarimeter at 25 ˚C. TLC analyses were carried out on plates coated with silica gel (hexane-EtOAc mixtures); spots were developed in an I2 chamber. For column chromatographic separations under gravity, column-grade silica gel (100-200 and 230-400 mesh) was employed.

Use of Tetrabutylammonium Borohydride-Iodine for the ­Reduction of Diester 5; Typical Procedure

Diester 5 (1.49 g, 5 mmol) and Bu4NBH4 (6.168 g, 24 mmol) were mixed in anhyd THF (60 mL) under N2 in a two-necked septum-capped round-bottom flask. I2 (3.048 g, 12 mmol) dissolved in anhyd THF (30 mL) was added under N2 at 0 ˚C over 1 h; the mixture was stirred at 25 ˚C for 4 h and refluxed for 12 h. The mixture was cooled to 25 ˚C and the excess hydride was carefully quenched with 3 N aq HCl (10 mL). After gas evolution had ceased, the reaction mixture was extracted with EtOAc (2 × 20 mL). The combined organic extracts were washed with aq NaHCO3 (15 mL), H2O (10 mL), and brine (10 mL) and dried (Na2SO4). The solvent was removed and the product was purified by column chromatography (silica gel, 100-200 mesh, hexane-EtOAc, 80:20) and recrystallized from hexane.

(±)-2,3-Diphenylbutane-1,4-diol [(±)-6]

Yield: 0.9 g (75%); mp 100-101 ˚C.

IR (KBr): 3290, 3060, 1601 cm-¹.

¹H NMR (400 MHz, CDCl3): δ = 2.2 (br s, 2 H), 3.1-3.4 (m, 2 H), 3.8-4.1(m, 4 H), 6.8-6.95 (m, 4 H), 7.0-7.2 (m, 6 H).

¹³C NMR (100 MHz, CDCl3): δ = 51.03, 65.5, 126.5, 128.1, 128.6, 140.6.

(-)-2,3-Diphenylbutane-1,4-diol [(-)-6]

Yield: 0.85 g (71%); 98% ee; [α]D ²5 -48.0 (c 0.404, CHCl3) {(Lit. [¹6] [α]D ²5 -48.2 (c 0.249, CHCl3)}.

Use of Tetrabutylammonium Borohydride-Iodomethane for the Reduction of Diester 10; Typical Procedure

Diester 10 (2.6 g, 5 mmol) and Bu4NBH4 (6.168 g, 24 mmol) were mixed in anhyd THF (60 mL) under N2 in a two-necked septum-capped round-bottom flask. MeI (3.4 g, 1.5 mL, 24 mmol) dissolved in anhyd THF (30 mL) was added under N2 at 0 ˚C over 1 h; the mixture was stirred at 25 ˚C for 4 h and refluxed for 12 h. It was then cooled to 25 ˚C and the excess hydride was carefully quenched with 3 N HCl (10 mL). After the gas evolution had ceased, the reaction mixture was extracted with EtOAc (2 × 20 mL). The combined organic extracts were washed with aq NaHCO3 (15 mL), H2O (10 mL), and brine (10 mL) and dried (Na2SO4). The solvent was removed under reduced pressure and the product was purified by column chromatography (silica gel, 100-200 mesh, hexane-EtOAc, 80:20) and recrystallized from hexane.

(-)-2,3-Diphenylbutane-1,4-diol [(-)-6]

Yield: 0.9 g (75%); 98% ee; mp 100-101 ˚C; [α]D ²5 -48.0 (c 0.560, CHCl3) {Lit. [¹6] [α]D ²5 -48.2 (c 0.249, CHCl3)}.

IR (KBr): 3290, 3060, 1601 cm-¹.

¹H NMR (400 MHz, CDCl3): δ = 2.2 (br s, 2 H), 3.1-3.4 (m, 2 H), 3.8-4.1 (m, 4 H), 6.8-6.95 (m, 4 H), 7.0-7.2 (m, 6 H).

¹³C NMR (100 MHz, CDCl3): δ = 51.03, 65.5, 126.5, 128.1, 128.6, 140.6.

(±)-2,3-Diphenylbutane-1,4-diol [(±)-6]

Yield: 0.89 g (74%); mp 100-101 ˚C.

(±)-3,4-Diphenyltetrahydrothiophene [(±)-1]

Na2S˙9H2O (freshly recrystallized from EtOH; 4.8 g, 20 mmol) was added to (±)-ditosylate 7 (2.63 g, 5 mmol) in EtOH (40 mL), and the mixture was refluxed for 24 h. H2O (10 mL) was then added and the mixture was extracted with Et2O (2 × 20 mL). The combined extracts were dried (Na2SO4) and the solvent was removed under reduced pressure. The product was purified by column chromatography (silica gel, 230-400 mesh, hexane).

Yield: 1.094 g, (91%); mp 109-110 ˚C.

¹H NMR (400 MHz, CDCl3): δ = 3.12-3.17 (m, 2 H), 3.28-3.32 (m, 2 H), 3.48-3.5 (m, 2 H), 7.1-7.26 (m, 10 H).

¹³C NMR (100 MHz, CDCl3): δ = 38.6, 55.8, 126.8, 127.4, 128.5, 140.5.

LCMS: m/z = 241 [M + 1].

(-)-3,4-Diphenyltetrahydrothiophene [(-)-1]

Compound (-)-1 was prepared from ditosylate (-)-7, by following the procedure described above for (±)-1.

Yield: 1.094 g (91%); 99% ee; mp 109-110 ˚C; [α]D ²5 -205 (c 1.08, CHCl3).

HPLC (Daicel Chiralcel OB-H, i-PrOH-hexane, 5:95, flow rate 1.0 mL/min, 254 nm): t R (R,R) = 7.7 min, t R (S,S) = 12.3 min.

¹H NMR (400 MHz, CDCl3): δ = 3.12-3.17 (m, 2 H), 3.28-3.32 (m, 2 H), 3.48-3.5 (m, 2 H), 7.1-7.26 (m, 10 H).

¹³C NMR (100 MHz, CDCl3): δ = 38.6, 55.8, 126.8, 127.4, 128.5, 140.5.

LCMS: m/z = 241 [M + 1].

Anal. Calcd for C16H16S: C, 79.95; H, 6.71; S, 13.34. Found: C, 79.95; H, 6.71; S, 13.64.

(+)-(1 R ,4 R )-1,4-Diphenylbutane-1,4-diol (13)

Bu4NBH4 (1.891 g, 7.6 mmol) was placed in a 100-mL three-neck round-bottom flask under a N2 atmosphere in anhyd THF (20 mL). To this I2 (0.934 g, 3.68 mmol) in anhyd THF (30 mL) was added under N2 at 0 ˚C over 1 h by use of a pressure equalizer. The diborane generated in situ was trapped as a BH3-THF complex. To this reagent, a soln of (S)-α,α-diphenyl-2-pyrrolidine methanol [(S)-DPP; 0.8 mmol] and trimethyl borate (1 mmol) in THF (8 mL)] was added and the mixture was stirred for 10 min. Then 12 (1 g, 4.6 mmol) dissolved in THF (25 mL) was added slowly to the reaction mixture with a pressure equalizer over 1 h at 10 ˚C, and the mixture was further stirred at 25 ˚C for 1 h. The reaction mixture was brought to 25 ˚C and carefully quenched with 2 N HCl (15 mL). The organic layer was separated and the aqueous layer was extracted with Et2O (2 × 20 mL). The combined extracts were washed with brine (10 mL) and dried (Na2SO4). The solvent was removed under reduced pressure and the product was purified by column chromatography (silica gel, 100-200 mesh, hexane-EtOAc, 75:25).

Yield: 1 g (90%); mp 63-65 ˚C; 90% ee; [α]D ²5 +52.6 (c 0.25, CHCl3) {Lit. [²¹] [α]D ²5 -58.5 (c 1.01, CHCl3) for (1S,4S)-13}.

HPLC (Daicel Chiralpak AD-H, i-PrOH-hexane, 10:90, flow rate 1.0 mL/min, 254 nm): t R (S,S) = 21 min, t R (R,R) = 22.5 min.

The non-racemic diol 13 (90% ee) was enriched by a reported procedure [²0] using l-proline and boric acid; this gave (+)-(1R,4R)-diol 13 in 98% ee.

IR (KBr): 3339, 3025, 1207, 990 cm-¹.

¹H NMR (400 MHz, CDCl3): δ = 1.8-2.0 (m, 4 H), 2.6-2.8 (br s, 2 H), 4.7 (m, 2 H), 7.2-7.3 (m, 10 H).

¹³C NMR (100 MHz, CDCl3): δ = 35.1, 74.3, 125.6, 127.0, 128.1, 144.6.

When using Bu4NBH4/MeI: Yield: 0.97 g (88%); 90% ee of (1R,4R); [α]D ²5 +52.68 (c 0.47, CHCl3) {Lit. [²¹] [α]D ²5 -58.5 (c 1.01, CHCl3, > 98% ee) for (1S,4S)}.

(+)-(2 S ,5 S )-2,5-Diphenyltetrahydrothiophene [(+)-2]

Dimesylate 14 (1.990 g, 5 mmol), prepared from (+)-(1R,4R)-diol 13 (98% ee), was taken up in DMSO (15 mL); Na2S˙9H2O (freshly recrystallized from EtOH; 4.8 g, 20 mmol) was added and the mixture was stirred at 5 ˚C for 24 h. H2O (10 mL) was then added and the contents were extracted with Et2O (3 × 20 mL). The combined extracts were concentrated and the product was purified by column chromatography (silica gel, 230-400 mesh, hexane).

Yield: 0.96 g (80%); 99% ee; mp 78 ˚C; [α]D ²5 +22 (c 0.5, CHCl3).

HPLC (Daicel Chiralcel OJ-H, i-PrOH-hexane, 20:80, flow rate 1.0 mL/min, 254 nm): t R (S,S) = 28.8 min, t R (R,R) = 42.5 min.

¹H NMR (400 MHz, CDCl3): δ = 2.11-2.16 (m, 2 H), 2.58-2.62 (m, 2 H), 4.82-4.86 (m, 2 H), 7.22-7.34 (m, 6 H), 7.46-7.47 (m, 4 H).

¹³C NMR (100 MHz, CDCl3): δ = 41.0, 54.3, 127.2, 128.4, 142.5.

LCMS: m/z = 241 [M + 1].

Anal. Calcd for C16H16S: C, 79.95; H, 6.71; S, 13.34. Found: C, 79.99; H, 6.74; S, 13.53.

(-)-(3 S ,6 S )-3,6-Diphenyl-1,2-dithiane [(-)-3]

Dimesylate 14 (1.99 g, 5 mmol), prepared from (+)-(1R,4R)-diol 13 (98% ee), was taken up in EtOH (20 mL); Na2S˙9H2O (freshly recrystallized from EtOH; 4.8 g, 20 mmol) was added and the mixture was stirred at 25 ˚C for 24 h. H2O (10 mL) was then added and the mixture was extracted with Et2O (3 × 20 mL). The combined extracts were concentrated and the product was purified by column chromatography (silica gel, 230-400 mesh, hexane).

Yield: 1.16 g (85%); mp 69-70 ˚C; 98% ee (based on ee of precursor 13). (However, X-ray structure data revealed the absence of the other enantiomer. Unfortunately, the corresponding racemic mixture could not be resolved by HPLC using the chiral columns OD, OB, OJ, and AD).

[α]D ²5 -4.2 (c 0.6, CHCl3).

¹H NMR (400 MHz, CDCl3): δ = 2.0-2.15 (m, 2 H), 2.53-2.61 (m, 2 H), 4.82-4.86 (m, 2 H), 7.22-7.36 (m, 10 H).

¹³C NMR (100 MHz, CDCl3): δ = 41.0, 54.3, 127.5, 127.6, 128.5, 142.5.

LCMS: m/z = 273 [M + 1].

Anal. Calcd for C16H16S2: C, 70.54; H, 5.92; S, 23.54. Found: C, 70.56; H, 5.94; S, 23.78.

Acknowledgment

We thank the CSIR (New Delhi) for research fellowships to G.B.R. and G.P.M. DST support through a J. C. Bose National Fellowship research grant to M.P. is gratefully acknowledged. We also thank the DST for the 400 MHz NMR facility under the FIST program and for the National Single-Crystal X-ray Diffractometer facility. Support of the UGC under the ‘University of Potential for Excellence’ and the Center for Advanced Study (CAS) programs is also gratefully acknowledged.

24

For compounds 1, 2, and 3, diffraction data were collected on a Bruker SMART APEX CCD area detector system using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Data reduction was carried out with SAINTPLUS, and the structures were solved and refined with SHELXS-97. All non-hydrogen atoms were refined anisotropically.
Crystal data for 1 (CCDC 711632): C16H16S, MW = 240.36, monoclinic, space group: P21, a = 10.363 (2) Å, b = 8.6732 (19) Å, c = 14.857 (3) Å, β = 91.314 (4)˚, V = 1335.0(5) ų, Z = 4, ρ = 1.196 Mg˙M-³, µ = 0.218 mm-¹, T = 298 (2) K. Of the 13820 reflections collected, 5194 were unique (R int = 0.0301). Refinement on all data converged at R1 = 0.0487, wR2 = 0.1107.
Crystal data for 2 (CCDC 711633): C16H16S, MW = 240.35, monoclinic, space group: P21, a = 13.453 (4) Å, b = 5.7139 (18) Å, c = 17.416 (5) Å, β = 99.656 (5)˚, V = 1319.8 (7) ų, Z = 4, ρ = 1.210 Mg˙M-³, µ = 0.220 mm-¹, T = 298 (2) K. Of the 12428 reflections collected, 4612 were unique (R int = 0.0626). Refinement on all data converged at R1 = 0.0750, wR2 = 0.1969.
Crystal data for 3 (CCDC 711634): C16H16S2, MW = 272.41, trigonal, space group: P3121, a = 9.2159 (14) Å, b = 9.2159 (14) Å, c = 14.647 (5) Å, α = 90˚, β = 90˚, γ = 120˚, V = 1077.3 (4) ų, Z = 3, ρ = 1.260 Mg˙M-³, µ = 0.350
mm-¹, T = 298 (2) K. Of the 6010 reflections collected, 1401 were unique (R int = 0.0326). Refinement on all data converged at R1 = 0.0412, wR2 = 0.1092.

24

For compounds 1, 2, and 3, diffraction data were collected on a Bruker SMART APEX CCD area detector system using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Data reduction was carried out with SAINTPLUS, and the structures were solved and refined with SHELXS-97. All non-hydrogen atoms were refined anisotropically.
Crystal data for 1 (CCDC 711632): C16H16S, MW = 240.36, monoclinic, space group: P21, a = 10.363 (2) Å, b = 8.6732 (19) Å, c = 14.857 (3) Å, β = 91.314 (4)˚, V = 1335.0(5) ų, Z = 4, ρ = 1.196 Mg˙M-³, µ = 0.218 mm-¹, T = 298 (2) K. Of the 13820 reflections collected, 5194 were unique (R int = 0.0301). Refinement on all data converged at R1 = 0.0487, wR2 = 0.1107.
Crystal data for 2 (CCDC 711633): C16H16S, MW = 240.35, monoclinic, space group: P21, a = 13.453 (4) Å, b = 5.7139 (18) Å, c = 17.416 (5) Å, β = 99.656 (5)˚, V = 1319.8 (7) ų, Z = 4, ρ = 1.210 Mg˙M-³, µ = 0.220 mm-¹, T = 298 (2) K. Of the 12428 reflections collected, 4612 were unique (R int = 0.0626). Refinement on all data converged at R1 = 0.0750, wR2 = 0.1969.
Crystal data for 3 (CCDC 711634): C16H16S2, MW = 272.41, trigonal, space group: P3121, a = 9.2159 (14) Å, b = 9.2159 (14) Å, c = 14.647 (5) Å, α = 90˚, β = 90˚, γ = 120˚, V = 1077.3 (4) ų, Z = 3, ρ = 1.260 Mg˙M-³, µ = 0.350
mm-¹, T = 298 (2) K. Of the 6010 reflections collected, 1401 were unique (R int = 0.0326). Refinement on all data converged at R1 = 0.0412, wR2 = 0.1092.

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Figure 1

Scheme 1 Synthesis of (±)-3,4-diphenyltetrahydrothiophene [(±)-1]

Scheme 2 Synthesis of (-)-(3R,4R)-3,4-diphenyltetrahydrothiophene [(-)-1]

Figure 2 ORTEP representation of the crystal structure of (-)-1; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity

Scheme 3 Synthesis of (+)-(2S,5S)-2,5-diphenyltetrahydrothiophene [(+)-2] and (-)-(3S,6S)-3,6-diphenyl-1,2-dithiane [(-)-3]

Figure 3 ORTEP representation of the crystal of structure (+)-2; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity

Figure 4 ORTEP representation of the crystal structure of (-)-3; thermal ellipsoids are drawn at 35% probability and all the hydrogens are omitted for the sake of clarity