Yb(OTf)₃-Catalyzed [4+2] Cycloaddition of Allenyltrimethylsilylthioketenes with Arylaldimines

Abstract

Yb(OTf)₃-catalyzed [4+2] cycloaddition of an in situ generated allenyltrimethylsilylthioketene with arylaldimines afforded unsaturated δ-thiolactams, one of which was converted into a known 4-azafluorenone, a synthetic precursor of onychine, in three steps.

allenyltrimethylsilylthioketene - arylaldimine - [4+2] cycloaddition - Yb(OTf)₃ - onychine

References and Notes

1a Barluenga J. Mateos C. Aznar F. Valdés C. J. Org. Chem.  2004,  69:  7114 

1b Mancheño OG. Arrayás RG. Carretero JC. J. Am. Chem. Soc.  2004,  126:  456 

1c Barluenga J. Mateos C. Aznar F. Valdés C. Org. Lett.  2002,  4:  1971 

1d Furman B. Dziedzic M. Tetrahedron Lett.  2003,  44:  6629 

2a Hattori K. Yamamoto H. J. Org. Chem.  1992,  57:  3264 

2b Ishihara K. Miyata M. Hattori K. Tada T. Yamamoto H. J. Am. Chem. Soc.  1994,  116:  10520 

2c Kobayashi S. Ishitani H. Nagayama S. Synthesis  1995,  1195 

2d Kobayashi S. Komiyama S. Ishitani H. Angew. Chem. Int. Ed.  1998,  37:  979 

2e Kobayashi S. Ishitani H. Chem. Rev.  1999,  99:  1069 

3 Bennett B. Okamoto I. Danheiser L. Org. Lett.  1999,  1:  641 

4a Shimada K. Akimoto S. Itoh H. Nakamura H. Takikawa Y. Chem. Lett.  1994,  1743 

4b Shimada K. Akimoto S. Takikawa Y. Kabuto C. Chem. Lett.  1994,  2286 

4c Koketsu M. Kanoh M. Itoh E. Ishihara H. J. Org. Chem.  2001,  66:  4099 

4d Koketsu M. Kanoh M. Yamamura Y. Ishihara H. Tetrahedron Lett.  2005,  46:  1479 

4e Aoyagi S. Sugimura K. Kanno N. Watanabe D. Shimada K. Takikawa Y. Chem. Lett.  2006,  992 

5 Aoyagi S. Hakoishi M. Suzuki M. Nakanoya Y. Shimada K. Takikawa Y. Tetrahedron Lett.  2006,  47:  7763 

6a de Almeida MEI. Braz FR. von Bulow MV. Gottleib OR. Maia JGS. Phytochemistry  1976,  15:  1186 

6b Goulart MOF. Santana AEG. de Oliveira AB. de Oliveira GG. Maia JGS. Phytochemistry  1986,  25:  1691 

6c Arango GJ. Cortes D. Cassels BK. Cave A. Merienne C. Phytochemistry  1987,  26:  2093 

6d Tadic D. Cassels BK. Cave A. Goulart MPF. de Oliveira AB. Phytochemistry  1987,  26:  1551 

6e Tadic D. Cassels BK. Cave A. Heterocycles  1988,  27:  407 

7a Koyama J. Sugita T. Suzuta Y. Irie H. Heterocycles  1979,  12:  1017 

7b Zhang J. El-Shabrawy O. El-Shabrawy MA. Schiff PL. Slatkin DJ. J. Nat. Prod.  1987,  50:  800 

7c Alves T. de Oliveira AB. Snieckus V. Tetrahedron Lett.  1988,  29:  2135 

7d Koyama J. Okatani T. Tagahara K. Heterocycles  1989,  29:  1648 

7e Bracher F. Synlett  1991,  95 

7f Nitta M. Ohnuma M. Iino Y. J. Chem. Soc., Perkin Trans. 1  1991,  1115 

7g Padwa A. Heidelbaugh TM. Kuethe JT. J. Org. Chem.  2000,  65:  2368 

8

A CHCl₃ (30 mL) solution of 1a (900 mg, 4.95 mmol), N-(p-methoxybenzyl)-2-bromobenzylidenamine (3f; 100 mg, 3.29 mmol) and Yb(OTf)₃ (408 mg, 0.66 mmol) was heated to reflux for 14 h. The resulting reaction mixture was subjected to column chromatography on silica gel (hexane-EtOAc, 10:1). 4f: yield: 1040 mg (65%); yellow plates; mp 138.8-139.2 °C. MS: m/z (%) = 485 (6) [M⁺], 470 (47) [M⁺ - Me], 412 (16) [M⁺ - TMS], 121 (100) [PMB]. IR (KBr): 2943, 1514, 1514, 1475, 1253, 1244, 875, 844 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.45 (s, 9 H), 1.93 (s, 3 H), 3.78 (s, 3 H), 3.99 (d, J = 14.5 Hz, 1 H), 5.34 (s, 1 H), 5.61 (s, 1 H), 5.67 (s, 1 H), 8.08 (d, J = 14.5 Hz, 1 H), 6.81 (d, J = 8.6 Hz, 2 H), 7.10-7.15 (m, 1 H), 7.21-7.25 (m, 2 H), 7.28 (d, J = 8.6 Hz, 2 H), 7.52 (d, J = 7.9 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 3.2 (q), 19.0 (q), 54.0 (t), 55.2 (q), 62.6 (d), 113.9 (d), 117.5 (dd), 123.1 (s), 127.5 (d), 127.8 (d), 128.1 (s), 129.5 (d), 129.7 (d), 133.6 (d), 136.6 (s), 141.4 (s), 141.9 (s), 142.7 (s), 159.1 (s), 195.6 (s). Anal. Calcd for C₂₄H₂₈BrNOSSi: C, 59.25; H, 5.80; N, 2.88. Found: C, 59.14; H, 5.89; N, 2.90.

9 Kochhar KS. Cottrell DA. Pinnick HW. Tetrahedron Lett.  1983,  24:  1323 

10a Davis FA. Jenkins R. Yochlovich SG. Tetrahedron Lett.  1978,  5171 

10b Davis FA. Awad SB. Jenkins RH. Billmers RL. Jenkins LA. J. Org. Chem.  1983,  48:  3071 

11

To a CHCl₃ (30 mL) solution of 4f (500 mg, 1.03 mmol) was added N-tosyl-3-phenyloxaziridine (340 mg, 1.23 mmol) portionwise at 0 °C and then the solution was stirred at r.t. for 30 min. The reaction was quenched with an excess amount of aq Na₂SO₃ solution and the organic layer was separated and dried over anhyd Na₂SO₄. After evaporation of the solvent, the residue was subjected to column chromatography on silica gel (hexane-EtOAc = 7:1). 6f: yield: 325 mg (67%); colorless oil. MS: m/z (%) = 469 (19) [M⁺], 454 (19) [M⁺ - Me], 121 (100) [PMB]. IR (neat): 2951, 1625, 1512, 1247, 1036, 845 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.39 (s, 9 H), 1.99 (s, 3 H), 3.47 (d, J = 14.6 Hz, 1 H), 3.78 (s, 3 H), 5.22 (d, J = 14.6 Hz, 1 H), 5.28 (s, 1 H), 5.55 (s, 1 H), 5.59 (s, 1 H), 6.81 (d, J = 6.6 Hz, 2 H), 7.10-7.20 (m, 1 H), 7.22 (d, J = 6.6 Hz, 2 H), 7.24-7.29 (m, 2 m), 7.53-7.55 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 2.0 (q), 18.6 (q), 47.0(dd), 55.1 (q), 61.1 (d), 113.6 (d), 115.7 (dd), 122.8 (s), 127.6 (d), 127.8 (d), 129.3 (s), 129.8 (d), 133.3 (d), 134.0 (s), 139.3 (s), 142.9 (s), 150.4 (s), 158.8 (s), 166.6 (s). Anal. Calcd for C₂₄H₂₈BrNO₂Si: C, 61.27; H, 6.00; N, 2.98. Found: C, 61.09; H, 6.07; N, 2.97.

12

A DMF solution (10 mL) of 6f (300 mg, 64 mmol), tri(o-tolyl)phosphine (19 mg, 6 mmol), Pd(OAc)₂ (7 mg, 3 mmol) and Et₃N (323 mg, 320 mmol) was stirred at 90 °C for 12 h under a N₂ atmosphere. After removal of DMF by distillation under reduced pressure, the residue was subjected to column chromatography on silica gel (hexane-EtOAc, 7:1). 7f: yield: 144 mg (58%); pale yellow plates; mp 142.7-144.0 °C. MS: m/z (%) = 389 (42) [M⁺], 374 (23) [M⁺ - Me], 121 (100) [PMB]. IR (KBr): 2951, 1619, 1579, 1247, 850 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.39 (s, 9 H), 2.40 (s, 3 H), 3.62 (s, 2 H), 3.73 (s, 3 H), 5.66 (br s, 2 H), 6.80 (d, J = 8.2 Hz, 2 H), 7.09 (d, J = 8.2 Hz, 2 H), 7.21 (t, J = 7.6 Hz, 1 H), 7.28 (t, J = 7.4 Hz, 1 H), 7.51 (d, J = 7.4 Hz, 1 H), 7.58 (d, J = 7.9 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 1.7 (q), 19.7 (q), 34.4 (t), 46.6 (t), 55.1 (q), 114.1 (d), 122.4 (s), 122.5 (d), 124.5 (d), 125.1 (d), 126.95 (d), 127.01 (d), 127.4 (d), 128.4 (s), 136.4 (s), 144.0 (s), 146.1 (s), 153.6 (s), 158.5 (s), 166.4 (s). Anal. Calcd for C₂₄H₂₇NO₂Si: C, 74.00; H, 6.99; N, 3.60. Found: C, 73.83; H, 7.15; N, 3.65.

13

A CHCl₃ (30 mL) solution of 7f (120 mg, 31 mmol) and p-toluenesulfonic acid monohydrate (205 mg, 108 mmol) was heated to reflux for 5 h. The reaction was quenched with an excess amount of aq NaHCO₃ solution and the organic layer was separated and dried over anhyd Na₂SO₄. After evaporation of the solvent, the residue was subjected to column chromatography on silica gel (hexane-EtOAc = 7:1). 8f: yield: 86 mg (88%); pale yellow solid; mp 162.2-163.8 °C (lit. [7g] 164-165 °C). MS: m/z (%) = 317 (10) [M⁺], 121 (100) [PMB]. IR (KBr): 2956, 1651, 1526, 1516, 1252, 1174, 1032, 842 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 2.32 (s, 3 H), 3.62 (s, 2 H), 3.73 (s, 3 H), 5.71 (br s, 2 H), 6.48 (s, 1 H), 6.82 (d, J = 8.6 Hz, 2 H), 7.12 (d, J = 8.6 Hz, 2 H), 7.25-7.35 (m, 2 H), 7.54 (d, J = 7.1 Hz, 1 H), 7.62 (d, J = 7.6 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 19.0 (q), 33.6 (t), 46.8 (t), 55.2 (q), 114.2 (d), 116.6 (d), 121.9 (s), 122.5 (d), 125.2 (d), 127.07 (d), 127.13 (d), 127.4 (d), 128.2 (s), 136.3 (s), 144.4 (s), 145.6 (s), 147.5 (s), 158.6 (s), 163.7 (s).