Pt-Catalyzed Regio- and Stereoselective Furylthiolation of Alkynes

Abstract

The Pt-catalyzed decarbonylative furylthiolation of ­terminal alkynes by furylthioesters took place regio- and stereo­selectively under toluene reflux to give vinylsulfides with cis-furyl group at β-carbon in moderate yields.

Key words

alkyne - carbothiolation - platinum - furylthiolation - thioester

References

• 1a Catalytic Heterofunctionalization   Togni A. Grützmacher H. Wiley-VCH; Weinheim: 2001.  p.217 
• 1b Han L.-B. Tanaka M. Chem. Commun.  1999,  395 
• 1c Beletskaya I. Moberg C. Chem. Rev.  1999,  99:  3435 
• 1d Ogawa A. In Main Group Metals in Organic Synthesis   Yamamoto H. Oshima K. Wiley-VCH; Weinheim: 2004.  p.813-866  
• 1e El AliB. Alper H. In Handbook of Organopalladium Chemistry for Organic Synthesis   Negishi E. Wiley-Interscience; New York: 2002.  Chap. VI.2.1.1.2.
• 1f Ogawa A. In Handbook of Organopalladium Chemistry for Organic Synthesis   Negishi E. Wiley-Interscience; New York: 2002.  Chap. VII.6.
• 1g Kondo T. Mitsudo T. Chem. Rev.  2000,  100:  3205 
• 1h Ogawa A. J. Organomet. Chem.  2000,  611:  463 
• 2 Yoshida H. Shirakawa E. Nakao Y. Honda Y. Hiyama T. Bull. Chem. Soc. Jpn.  2001,  74:  637 ; and references therein
• 3a Chatani N. Amishiro N. Mori T. Yamashita S. Murai S. J. Org. Chem.  1995,  60:  1834 
• 3b Obora Y. Tsuji Y. Kawamura T. J. Am. Chem. Soc.  1995,  117:  9814 
• 4 Kokubo K. Matsumasa K. Miura M. Nomura M. J. Org. Chem.  1996,  61:  6941 
• 5 Kuniyasu H. Kurosawa H. Chem.-Eur. J.  2002,  8:  2660 ; and references cited therein
• 6 Sugoh K. Kuniyasu H. Sugae T. Ohtaka A. Takai Y. Tanaka A. Machino C. Kambe N. Kurosawa H. J. Am. Chem. Soc.  2001,  123:  5108 
• 7 Hirai T. Kuniyasu H. Kato T. Kurata Y. Kambe N. Org. Lett.  2003,  5:  3871 
• 8 Hirai T. Kuniyasu H. Kambe N. Chem. Lett.  2004,  33:  1148 
• 9 Hirai T. Kuniyasu H. Kambe N. Tetrahedron Lett.  2005,  46:  117 
• For the synthetic utility of vinyl sulfides, see:
• 11a Trost BM. Lavoie AC. J. Am. Chem. Soc.  1983,  105:  5075 
• 11b Magnus P. Quagliato D. J. Org. Chem.  1985,  50:  1621 

10

The furylthioesters (1) were facilely prepared by the reaction of the corresponding acid chlorides with thiols in the presence of pyridine.

12

Experimental Procedure for Compound 3a.
Into a two-necked 3 mL flask were added (2-furyl)C(O)SPh (1a, 204.3 mg, 1.0 mmol), Pt(PPh₃)₄ (62.2 mg, 0.05 mmol), toluene (0.5 mL) and 1-octyne (2a, 132.2 mg, 1.2 mmol). After the solution was vigorously refluxed for 24 h, the resultant reaction mixture was separated by preparative TLC (PTLC) using pentane as an eluent to give the desired (Z)-1-(2-furyl)-2-(SPh)-1-hexene (3a) in 78% (223.4 mg) yield as a yellow oil. The stereo- and regiochemistry was determined by NOE and ¹³C-¹³C NMR measurement. Data of 3a: ¹H NMR (400 MHz, CDCl₃): δ = 7.42-7.39 (m, 3 H), 7.33-7.24 (m, 3 H), 6.87 (d, J = 3.2 Hz, 1 H), 6.62 (s, 1 H), 6.44-6.43 (m, 1 H), 2.25 (t, J = 7.4 Hz, 2 H), 1.55-1.48 (m, 2 H), 1.26-1.19 (m, 6 H), 0.86 (t, J = 7.0 Hz, 3 H). NOE experiment: irradiation at the methylene triplet at δ = 2.25 ppm resulted in a 7.8% enhancement at δ = 6.87 ppm (vinyl singlet). ¹³C NMR (100 MHz, CDCl₃): δ = 151.7, 140.8, 134.6, 133.0, 131.7, 128.7, 127.0, 119.2, 111.4, 109.8, 37.7, 31.6, 29.0, 28.6, 22.6, 14.2. IR (neat): 3146, 3117, 3059, 3018, 2928, 2856, 2232, 1947, 1879, 1728, 1614, 1583, 1538, 1486, 1477, 1440, 1379, 1324, 1302, 1269, 1238, 1177, 1150, 1116, 1086, 1068, 1017, 943, 885, 802, 735, 704, 692 cm^-1. MS (EI): m/e (%) = 286 (100) [M⁺]. Anal. Calcd for C₁₈H₂₂OS: C, 75.48; H, 7.74; S, 11.19. Found: C, 75.32; H, 7.68; S, 11.14.

13

Into a two-necked 3 mL flask were added Pt(PPh₃)₄ (37.3 mg, 0.03 mmol), thioester 1d (282.0 mg, 1.0 mmol), diethynylbenzene 2g (63.1 mg, 0.5 mmol) and toluene (0.5 mL). The reaction mixture was vigorously refluxed for 24 h under a nitrogen atmosphere and cooled to r.t. After the resultant mixture was filtrated through Celite, the product was reprecipitated from CH₂Cl₂ solution with pentane (isolated yield 70% based on 2g). Yellow solid: ¹H NMR (400 MHz, CDCl₃): δ = 7.50-7.19 (m, 14 H), 7.09-7.06 (m, 4 H), 6.89-6.86 (m, 4 H), 2.31 (s, 3 H), 2.21 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 154.0, 149.3, 140.1, 135.6, 131.6, 130.1, 129.5, 129.1, 127.9, 124.8, 122.3, 119.0, 118.7, 116.5, 111.1, 21.2, 9.1. MS (EI): m/e (%) = 634 (100) [M⁺]. UV: λ_max = 387 nm. Anal. Calcd for C₄₂H₃₄O₂S₂: C, 79.46; H, 5.40. Found: C, 78.27; H, 5.39.