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Synthesis 2007(20): 3117-3124  
DOI: 10.1055/s-2007-990787
PAPER
© Georg Thieme Verlag Stuttgart · New York

Highly Regioselective Synthesis of Substituted Pyrroles Utilizing Low-Valent Titanium Reagent

Daqing Shi*a,b, Guolan Doub, Chunling Shic, Zhengyi Lib, Shun-Jun Jia
a College of Chemistry and Chemical Engineering, Key Laboratory of Organic Synthesis of Jiangsu Province, Suzhou University, Suzhou 215123, P. R. of China
b College of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou 221116, P. R. of China
c College of Chemistry and Chemical Engineering, Southeast University, Nanjing 210009, P. R. of China
e-Mail: dqshi@263.net;
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Publication History

Received 6 June 2007
Publication Date:
21 September 2007 (online)

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Abstract

A short and efficient synthesis of substituted pyrroles was accomplished in good yields via the novel coupling cyclization reaction of 1,3-diketones with imines promoted by low-valent titanium reagent. High regioselectivity was achieved and the structures of two of the products were confirmed by X-ray diffraction studies.

Key words

low-valent titanium - pyrrole - regioselectivity

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Crystal data for 3p: C19H20Cl2FN; M = 472.36, colorless block crystal, 0.52 × 0.38 × 0.18 mm, monoclinic, space group P21/n, a = 10.432 (2) Å, b = 9.744 (2) Å, c = 24.034 (5) Å, β = 99.51 (2)°, V = 2409.5 (8) Å3, Z = 4, Dc = 1.738 g.cm-3, F(000) = 976, µ(MoKα) = 0.294 mm-1. Intensity data were collected on a Siemens P4 diffractometer with graphite monochromated MoK α radiation (λ = 0.71073 Å) using the ω scan mode with 3.10° < θ < 25.50°. 5222 unique reflections were measured and reflections with I > 2 σ (I) were used in the Fourier techniques. The final refinement was converged to R = 0.0544 and wR = 0.1911.

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Crystal data for 5d: C23H14Br2F3N; M = 521.17, colorless block crystal, 0.54 × 0.16 × 0.09 mm, monoclinic, space group P2/c, a = 19.480 (3) Å, b = 5.76800(18) Å, c = 19.430 (3) Å, β = 114.186 (3)°, V = 1991.5 (4) Å3, Z = 4, Dc = 1.738 g.cm-3, F(000) = 1024, µ(MoKα) = 4.107 mm-1. Intensity data were collected on a Smart-1000 diffractometer with graphite monochromated MoKα radiation (λ = 0.71073 Å) using the ω scan mode with 2.298° < θ < 21.182°. 9670 unique reflections were measured and reflections with
I > 2 σ (I) were used in the Fourier techniques. The final refinement was converged to R = 0.0621 and wR = 0.1450.