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Synlett 2015; 26(04): 479-483
DOI: 10.1055/s-0034-1379320
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© Georg Thieme Verlag Stuttgart · New York

Electrophile-Promoted Cyclization of Propargylic Amides

Rita Bukšnaitienė
Department of Organic Chemistry, Faculty of Chemistry, Vilnius University, Naugarduko 24, 03225 Vilnius, Lithuania   Fax: +370(5)2330987   eMail: inga.cikotiene@chf.vu.lt
,
Inga Čikotienė*
Department of Organic Chemistry, Faculty of Chemistry, Vilnius University, Naugarduko 24, 03225 Vilnius, Lithuania   Fax: +370(5)2330987   eMail: inga.cikotiene@chf.vu.lt
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Publikationsverlauf

Received: 07. August 2014

Accepted after revision: 21. September 2014

Publikationsdatum:
17. Oktober 2014 (online)

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Abstract

Electrophilic cyclization of N-(3-arylprop-2-ynyl)amides to functionalized 4H-1,3-oxazines is described. It was found that the presence of an electron-rich aryl group next to the triple bond is crucial for a smooth and highly regioselective 6-endo-dig ring closure process.

Key words

propargylic amides - electrophile - cyclization - ­oxazines - oxazolines

Supporting Information

    for this article is available online at http://www.thieme-connect.com/products/ejournals/journal/ 10.1055/s-00000083. Included are spectroscopic data of synthesized compounds and copies of NMR spectra.
  • Supporting Information
 

  • References and Notes

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  • 11 General Procedures for the Synthesis of 6-Aryl-5-iodo-2-phenyl-4H-1,3-oxazines 2: To the solution of the corresponding N-[(3-substituted)prop-2-ynyl]benzamide 1 (1 mmol) in CH2Cl2 (5 mL) N-iodosuccinimide (0.23 g, 1 mmol; method A) or phenyl hypochloroselenoite (95.96 mg, 0.5 mmol) together with potassium tert-butanoate (0.5 mmol; method B), or 1-methoxyisochromane (90.2 mg, 0.55 mmol) followed by trimethylsilyl triflate (0.09 mL, 0.5 mmol; method C) were added. The mixture was stirred at r.t. When reaction was complete (TLC), the solution was quenched with aq sodium thiosulfate. The organic layer was separated, washed with aq sodium thiosulfate (2 × 20 mL), and H2O (2 × 20 mL), and dried over anhyd Na2SO4. After filtration and evaporation of the solvent under reduced pressure, the residue was purified by flash column chromatography eluting with hexane–EtOAc mixtures. 5-Iodo-6-(4-methoxyphenyl)-2-phenyl-4H-1,3-oxazine (2aa): white solid; mp 119–120 °C; yield: 72%. 1H NMR (400 MHz, CDCl3): δ = 3.86 (s, 3 H, OMe), 4.56 (s, 2 H, CH2), 6.96 (d, 3 J = 8.8 Hz, 2 H, ArH), 7.40 (t, 3 J = 7.6 Hz, 2 H, ArH), 7.48 (tt, 3 J = 7.6 Hz, 4 J = 2.4 Hz, 1 H, ArH), 7.63 (d, 3 J = 8.8 Hz, 2 H, ArH), 7.95–7.97 (m, 2 H, ArH). 13C NMR (100 MHz, CDCl3): δ = 55.2 (CH2), 55.4 (OMe), 69.8 (CI), 113.6 (ArC), 126.6 (ArC), 127.4 (ArC), 128.4 (ArC), 130.5 (ArC), 131.1 (ArC), 131.7 (ArC), 147.7 (Csp 2), 153.7 (Csp 2), 160.6 (ArC). HRMS (ESI): m/z [M + H+] calcd for C17H15INO2: 392.0142; found: 392.0148. Compounds 1–11 were also fully characterized by IR, 1H NMR, 13C NMR spectroscopic and microanalytical data.