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Synlett 2007(7): 1109-1111  
DOI: 10.1055/s-2007-977435
LETTER
© Georg Thieme Verlag Stuttgart · New York

Domino Addition/N-C Heterocyclization of Azides with Allenyl Magnesium Bromide: Rapid Synthesis of 5-Butynyl-1,2,3-triazoles [1]

Syed Shafi, Abid Hussain Banday, Tabasum Ismail, H. M. Sampath Kumar*
Regional Research Laboratory, Canal Road, Jammu Tawi 180001, India
Fax: +91(191)2548607; e-Mail: hmskumar@yahoo.com;
Further Information

Publication History

Received 20 August 2006
Publication Date:
13 April 2007 (online)

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Abstract

1,5-Disubstituted 1,2,3-triazoles are formed through a novel domino reaction involving the addition of aromatic azides to an excess of allenylmagnesium bromide with concomitant N-C heterocyclization followed by the addition of another mole of allenylmagnesium species to generate the terminal acetylenic product in moderate to high yields.

Key words

allenylmagnesium bromide - azides - 5-but-1,2,3-tri­azoles

1

RRL communication No. SCL-6/07.

1

RRL communication No. SCL-6/07.

26

In a typical procedure, to a suspension of magnesium turnings (1.6 g, 0.07 mol) in anhyd THF with mercury(II) chloride (10 mg, 0.125 w/w of propargyl bromide) was added propargyl bromide (7.5 mL of an 80 wt% solution in toluene, 0.07 mol) in small portions while stirring the reaction mixture at r.t. (Note: A small crystal of iodine is generally required to promote formation of the Grignard reagent). The mixture was stirred at r.t. for 15 min to give a cloudy light green solution. The allenylmagnesium bromide generated as above was cooled to ambient temperature and to it was added dropwise a solution of p-methoxyphenyl azide (1 g, 0.007 mol) and stirring was continued at ambient temperature for 10 min followed by quenching with an aq NH4Cl solution (10 mL) and diluting with EtOAc (50 mL). The organic layer was separated and the aqueous layer was extracted with EtOAc (2 × 20 mL). The combined organic layers were dried (anhyd Na2SO4) and evaporated under reduced pressure to afford the crude product which was subjected to chromatography (basic aluminum oxide, elution: n-hexane-EtOAc gradient) to afford pure 5-but-3-yn-1-yl-1-(4-methoxyphenyl)-1H-1,2,3-triazole as a brown colored syrupy liquid (1.066 g,70%).
IR: 3293, 2957, 2925, 2855, 1722, 1597, 1546, 1501, 1457, 1253, 1120, 1092, 1069, 917, 765, 693, 650 cm-1. 1H NMR (CDCl3): δ = 2.05 (t, J = 2.5 Hz, 1 H), 2.50 (m, 2 H), 2.90 (t, J = 7.3 Hz, 2 H), 3.92 (s, 3 H), 7.30 (d, J = 8.9 Hz, 2 H), 7.45 (d, J = 8.9 Hz, 2 H ), 7.80 (s, 1 H). 13C NMR (500 MHz, CDCl3): δ = 17.83, 22.97, 55.64, 70.07, 81.81, 114.70, 126.84, 128.79, 132.48, 136.34, 162.51. ESI-MS: m/z = 227 [M+], 250 [M + Na]. Anal. Calcd for C13H13N3O: C, 68.71; H, 5.77; N, 18.49; O, 7.04. Found: C, 68.60; H, 5.81; N, 18.60; O, 6.99.