Regioselective Synthesis of New 1-Aminopyrroles and 1-Amino-4,5,6,7-tetrahydroindoles by One-Pot ‘Conjugate Addition/Cyclization’ Reactions of 1,3-Bis(silyl enol ethers) with 1,2-Diaza-1,3-butadienes

Abstract

Unknown functionalized 1-aminopyrroles and 1-amino-4,5,6,7-tetrahydroindoles were prepared under mild conditions and with excellent yields by one-pot ‘conjugate addition/cyclization’ reactions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-butadienes.

cyclizations - 1,2-diaza-1,3-butadienes - N-heterocycles - pyrroles - silyl enol ethers

References and Notes

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18

General Procedure for the Synthesis of 3 and 5: To a CH₂Cl₂ solution (12 mL) of 1,2-diaza-1,3-butadiene 1 (2.0 mmol) was added 1,3-bis(silyl enol ether) 2 or 4 (2.4 mmol) and freshly dried ZnCl₂ (0.055 g, 0.4 mmol) at 20 °C. The solution was stirred for 12 h at r.t. and subsequently TFA (0.3 mL) was added. The solvent was removed in vacuo and the residue was purified by column chromatography [silica gel, heptane → heptane-EtOAc (30:70)].
Synthesis of 3d: Prepared from 1,2-diaza-1,3-butadiene 1a (0.370 g, 2.0 mmol), 1-tert-butoxy-1,3-bistrimethylsilyl-oxybuta-1,3-diene (2d; 0.726 g, 2.4 mmol) and ZnCl₂ (0.055 g, 0.4 mmol). Compound 3d was purified by chromatog-raphy and crystallized (EtOH) as a colorless solid (0.527 g, 81%); mp 178-180 °C. ¹H NMR (300 MHz, DMSO-d ₆): δ = 1.25 (t, ³ J = 7.1 Hz, 3 H, CH₂CH ₃), 1.42 (s, 9 H, t-Bu), 2.29 (s, 3 H, CMe), 3.34 (dd, ² J = 17.0 Hz, 1 H, CCH₂), 3.44 (dd, ² J = 17.0 Hz, 1 H, CCH₂), 4.16 (q, ³ J = 7.1 Hz, 2 H, CH ₂CH₃), 6.19 (br, 2 H, CONH₂), 6.23 (s, 1 H, H_Hetar), 9.06 (s, 1 H, NNHCO). ¹³C NMR (62.9 MHz, DMSO-d ₆): δ = 10.5 (CH₂ CH₃), 14.6 (NCCH₃), 27.9 [C(CH₃)₃], 32.2 (CCH₂CO), 58.9 (OCH₂), 80.6 [OC(CH₃)₃], 106.2 (CH_Hetar), 108.7 (CCOO), 126.5, 136.6 (NC_Hetar), 157.2, 164.4, 169.1 (CO). IR (KBr): 3405 (s), 3270 (m), 2981 (m), 2934 (w), 2907 (w), 1740 (s), 1675 (s), 1576 (m), 1531 (m), 1477 (m), 1457 (m), 1414 (m), 1388 (m), 1371 (m), 1352 (m), 1229 (s), 1146 (s), 1081 (s), 1021 (w), 849 (w), 773 (w), 627 (w), 602 (w), 483 (w) cm^-1. MS (EI, 70 eV): m/z (%) = 325 (11) [M⁺], 269 (18), 224 (100), 207 (26), 166 (27), 57 (79). HRMS (EI, 70 eV): m/z [M]⁺ calcd for C₁₅H₂₃N₃O₅: 325.16322; found: 325.162992.

19

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