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Synlett 2007(16): 2553-2556  
DOI: 10.1055/s-2007-986669
LETTER
© Georg Thieme Verlag Stuttgart · New York

Convenient Synthesis of 4-Methylenecyclobutenones and Their Synthetic Utility as Allenylketene Precursors

Shigenobu Aoyagi*, Kazuma Kikuchi, Kazuaki Shimada, Yuji Takikawa
Department of Chemical Engineering, Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551, Japan
Fax: +81(248)732173; e-Mail: aoyagi@jp-noc.co.jp;
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Publication History

Received 24 February 2007
Publication Date:
12 September 2007 (online)

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Abstract

Thermal reaction of alkynyl propargyl sulfides 1 in the presence of n-BuN3 followed by moist silica gel treatment afforded 4-methylenecyclobutenones 4 in moderate yields. Photogeneration of allenylketenes 5 from 4 in the presence of amine or methanol gave 3,4-pentadienamides 6 or methyl 3,4-pentadienates 7, respectively. Similar reaction in the presence of aldimines afforded unsaturated δ-lactams 9 in good yields.

Key words

alkynyl propargyl sulfides - 4-methylenecyclobutenones - allenylketenes - [4+2]-cycloaddition - unsaturated δ-lactams

7

A benzene solution (20 mL) of 1a (500 mg, 2.01 mmol) and n-BuN3 (598 mg, 6.04 mmol) was heated to reflux for 14 h. Decantation (hexane) of the residue after removal of solvent and excess amount of n-BuN3 followed by evaporation afforded 3a; yield: 4.87 mg (84%); pale yellow oil. MS: m/z = 287 (95) [M+], 230 (100) [M+ - n-Bu]. IR (neat): 2957, 2930, 1708, 1444, 1361, 867, 764, 691 cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.99 (t, J = 7.3 Hz, 3 H), 1.51-1.61 (m, 2 H), 1.71-1.76 (m, 2 H), 3.81 (t, J = 7.2 Hz, 2 H), 5.09 (d, J = 1.5 Hz, 1 H), 5.17 (d, J = 1.5 Hz, 1 H), 7.32-7.47 (m, 6 H), 7.61-7.65 (m, 2 H), 7.90-7.94 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 13.9 (q), 20.5 (t), 33.7 (t), 51.6 (t), 98.5 (dd), 127.2 (d), 127.8 (d), 128.1 (d), 128.2 (d), 128.7 (d), 129.1 (d), 129.3 (s), 130.8 (s), 151.1 (s), 151.8 (s), 157.8 (s), 161.9 (s). Anal. Calcd for C21H21N: C, 87.76; H, 7.36; N, 4.87. Found: C, 87.44; H, 7.41; N, 4.67.

8

A benzene solution (20 mL) of 1a (500 mg, 2.01 mmol) and n-BuN3 (598 mg, 6.04 mmol) was heated to reflux for 14 h. The resulting solution was subjected to column chromatography on silica gel (hexane-EtOAc = 20:1) to yield 4a (337 mg, 72%) as a pale yellow oil. UV (hexane): λmax = 332 (ε = 10500), 283 (ε = 13500) nm. MS: m/z = 232 (100) [M+], 204 (79) [M+ - CO]. IR (neat): 3062, 1773, 1751, 1445, 1360, 722, 692 cm-1. 1H NMR (400 MHz, CDCl3): δ = 5.02 (d, J = 1.7 Hz, 1 H), 5.27 (d, J = 1.7 Hz, 1 H), 7.35-7.37 (m, 3 H), 7.50-7.51 (m, 3 H), 7.76-7.78 (m, 2 H), 7.82-7.85 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 95.7 (dd), 127.5 (d), 127.83 (d), 128.78 (d), 129.1 (d), 129.4 (s), 130.1 (d), 131.0 (s), 131.5 (d), 155.5 (s), 157.0 (s), 172.4 (s), 188.2 (s). Anal. Calcd for C17H12O: C, 87.90; H, 5.21. Found: C, 87.81; H, 5.33.

11

A THF solution (20 mL) of 4h (300 mg, 1.31 mmol) and BnNH2 (703 mg, 6.57 mmol) was irradiated using high pressure Hg lamp at r.t. for 8 h under N2. The residue after removal of solvent was subjected to column chromatog-raphy on silica gel (hexane-EtOAc = 5:1) to give 6h-Bn (317 mg, 72%) as a pale yellow oil. MS: m/z = 335 (3) [M+], 262 (51) [M+ - Me3Si], 91 (100) [Bn]. IR (neat): 3304, 3062, 3031, 2956, 1938, 1636, 1515, 1495, 1249, 846, 733, 696 cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.08 (s, 9 H), 2.97 (s, 1 H), 4.31 (d, J = 2.1 Hz, 1 H), 4.33 (d, J = 2.1 Hz, 1 H), 5.04 (d, J = 12.1 Hz, 1 H), 5.10 (d, J = 12.1 Hz, 1 H), 6.14 (br s, 1 H), 7.00-7.03 (m, 2 H), 7.07-7.14 (m, 3 H), 7.17-7.22 (m, 3 H), 7.27-7.30 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = -1.5 (q), 41.2 (d), 43.4 (t), 79.9 (t), 103.1 (s), 126.0 (d), 127.0 (d), 127.1 (d), 127.3 (d), 128.3 (d), 128.4 (d), 136.5 (s), 138.4 (s), 171.7 (s), 210.0 (s). Anal. Calcd for C21H25NOSi: C, 75.18; H, 7.51; N, 4.17. Found: C, 75.11; H, 7.50; N, 4.27.

12

A MeOH solution (20 mL) of 4h (300 mg, 1.31 mmol) was irradiated using high pressure Hg lamp at r.t. for 5 h under N2. The residue after removal of excess amount of MeOH was subjected to column chromatography on silica gel (hexane-EtOAc = 7:1) to provide 7h (322 mg, 94%) as a pale yellow oil. MS: m/z = 260 (44) [M+], 245 (77) [M+ - Me], 187 (65) [M+ - Me3Si], 73 (100) [Me3Si]. IR (neat): 2952, 1948, 1731, 1715, 1251, 1154, 850, 695 cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.18 (s, 9 H), 3.19 (s, 1 H), 3.69 (s, 3 H), 5.17 (d, J = 11.8 Hz, 1 H), 5.27 (d, J = 11.8 Hz, 1 H), 7.18-7.21 (m, 1 H), 7.25-7.30 (m, 2 H), 7.32-7.39 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = -1.7 (q), 38.8 (d), 51.5 (q), 79.5 (t), 101.4 (s), 126.0 (d), 126.7 (d), 128.4 (d), 137.4 (s), 173.3 (s), 173.3 (s), 210.9 (s). Anal. Calcd for C15H20O2Si: C, 69.19; H, 7.74. Found: C, 69.28; H, 7.96.

15

To an ethereal solution (50 mL) of 8c prepared from piperidine (335 mg, 3.94 mmol) according to the reported procedure,13 4h (300 mg, 1.31 mmol) was added and the mixture was irradiated using high pressure Hg lamp at r.t. for 8 h under N2. The residue after removal of solvent was subjected to column chromatography on silica gel (hexane-EtOAc = 5:1) to give 9c (291 mg, 71%) as a colorless oil. MS: m/z = 311 (10) [M+], 296 (100) [M+ - Me]. IR (neat): 2939, 1623, 1462, 1442, 1269, 1251, 878, 843 cm-1. 1H NMR (400 MHz, CDCl3): δ = -0.15 (s, 9 H), 1.49-1.57 (m, 1 H), 1.67-1.74 (m, 3 H), 1.79-1.87 (m, 1 H), 1.95-1.99 (m, 1 H), 2.58 (td, J = 2.6, 12.8 Hz, 1 H), 4.14 (br d, 1 H), 4.64-4.71 (m, 1 H), 4.68 (s, 1 H), 5.18 (s, 1 H), 7.11-7.12 (m, 2 H), 7.33-7.36 (m, 3 H). 13C NMR (100 MHz, CDCl3): δ = 0.93 (q), 25.1 (t), 25.7 (t), 36.2 (t), 43.9 (dd), 61.8 (d), 118.6 (d), 127.8 (d), 129.0 (d), 129.7 (d), 133.8 (s), 138.8 (s), 144.9 (s), 155.2 (s), 165.6 (s). Anal. Calcd for C19H25NOSi: C, 73.26; H, 8.09; N, 4.50. Found: C, 73.08; H, 8.15; N, 4.44.