A simple and environmentally friendly method to prepare S-heterocycles by cyclization of aromatic thiols and diols with H2O as a byproduct is described. The Sc(OTf)3-catalyzed dehydrative cyclizations of aromatic thiols and diols provided the corresponding thiopyran and thiophene derivatives. Control experiments were also performed to obtain insights into the reaction pathway
9 Di-2-naphthyl disulfide was obtained in a quantitative yield (see also Scheme 4a).
10 Under similar reaction conditions at 150 °C, 3aa was obtained in an isolated yield of 55%. In addition, when the reaction was performed with 10 mol% of Sc(OTf)3, 3aa was obtained in 66% yield.
11 Di-2-naphthyl disulfide was obtained in a quantitative yield.
123ja: HRMS: m/z calcd for C10H9F3S: 218.03771; found: 218.03755. 4ja: HRMS: m/z calcd for C10H7F3S: 216.02206; found: 216.02411.
133,3-Dimethyl-2,3-dihydro-1H-naphtho[2,1-b]thiopyran (3af) and 1,1-Dimethyl-2,3-dihydro-1H-naphtho[2,1-b]thiopyran (3′af); Typical Procedure
A vial was charged with naphthalene-2-thiol (1a; 16.0 mg, 0.1 mmol), Sc(OTf)3 (2.5 mg, 5.0 mol%), and 3-methylbutane-1,3-diol (2f; 0.1 mL), and the mixture was stirred at 165 °C for 16 h. The mixture was then diluted with EtOAc (1.0 mL) and H2O (1.0 mL) was added. The mixture was stirred well, then the organic layer was separated and the aqueous layer was extracted with EtOAc (3 × 1.0 mL). The organic layers were combined, dried (Na2SO4), and concentrated under reduced pressure. The residue was purified by PTLC (Wakogel B-5F, hexane–EtOAc, 50:1) to give a mixture of 3af and 3′af as a white oil; yield: 18.9 mg (83%).
3af Pale-yellow oil. 1H NMR (400 MHz, CDCl3): δ = 1.45 (s, 6 H), 2.09 (t, J = 6.8 Hz, 2 H), 3.29 (t, J = 6.5 Hz, 2 H), 7.13 (d, J = 8.5 Hz, 1 H), 7.39 (t, J = 7.4 Hz, 1 H), 7.50 (t, J = 7.1 Hz, 1 H), 7.57 (d, J = 8.5 Hz, 1 H), 7.75 (d, J = 8.5 Hz, 1 H), 7.93 (d, J = 8.5 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 23.3, 29.2 (2 C), 37.6, 41.5, 121.8, 124.3, 125.3, 126.1, 126.4, 126.5, 128.6, 130.9, 131.2, 132.8. HRMS (GC-MS): m/z [M+] calcd for C15H16S: 228.0973; found: 228.1013.
3′af1H NMR: δ = 1.69 (s, 6 H), 2.18–2.20 (m, 2 H), 3.00–3.01 (m, 2 H), 7.13 (d, J = 8.4 Hz, 1 H), 7.33 (t, J = 7.6 Hz, 1 H), 7.41–7.44 (m, 1 H), 7.49 (d, J = 8.4 Hz, 1 H), 7.71–7.73 (m, 1 H), 8.30 (d, J = 7.8 Hz, 1 H). HRMS (GC-MS): m/z [M+] calcd for C15H16S: 228.09973; found: 228.1010.
14 Under N2, naphthalene-2-thiol and di-2-naphthyl disulfide were recovered in yields of 28% and 13%, respectively. Under O2, naphthalene-2-thiol and di-2-naphthyl disulfide were not detected in a 1H NMR analysis (the 1H NMR spectra were messy).
15 Naphthalene-2-thiol was not detected, and di-2-naphthyl disulfide was obtained (TEMPO: 29%, DPPH: 14%).
16 Di-2-naphthyl disulfide was recovered (TEMPO: 58%, DPPH: 41%).
17 Under similar reaction conditions without the Sc(OTf)3 catalyst, the cyclized products 3af and 3′af were not detected in the 1H NMR analysis, and only the starting material 7a was recovered.
18a
Dénès F,
Pichowicz M,
Povie G,
Renaud P.
Chem. Rev. 2014; 114: 2587
