Efficient Regioselective Synthesis of Indole <i>N</i>-Carboximidamides and <i>N</i>-Carboximidoates by a Sequential Aza-Wittig/Ag(I)-Catalyzed Cyclization
作者:Nian-Yu Huang、Ming-Guo Liu、Ming-Wu Ding
DOI:10.1021/jo901362c
日期:2009.9.4
An efficient Ag(I)-catalyzed regioselectivecyclization of (2-alkynylphenyl)guanidine or (2-alkynylphenyl)isourea to indole N-carboximidamides or N-carboximidoates has been developed. The approach has the advantages of high regioselectivity, mild reaction conditions, easily accessible starting materials, and good yields.
Synthesis of Indolyl Imidazole Derivatives via Base-Promoted Tandem Reaction of <i>N</i>-[2-(1-Alkynyl)phenyl]carbodiimides with Isocyanides
作者:Wenyan Hao、Yuanyuan Jiang、Mingzhong Cai
DOI:10.1021/jo402552c
日期:2014.4.18
An efficientroute to indolyl imidazole derivatives has been developed through a base-promoted tandemreaction of N-[2-(1-alkynyl)phenyl]carbodiimides with isocyanides in DMSO at 40 °C. The present tandem process allows the assembly of a variety of indolyl imidazole derivatives in moderate to good yields.
Thermal C<sup>2</sup>−C<sup>6</sup> Cyclization of Enyne−Carbodiimides: Experimental Evidence Contradicts a Diradical and Suggests a Carbene Intermediate
Mechanistic details of the thermal C(2)-C(6) cyclization of enyne-carbodiimides are investigated. A variety of product and kinetic studies on solvent and substituent effects open the way for a deeper mechanistic understanding. Nonlinear Hammett correlations suggest that a change of mechanism takes place: the thermal C(2)-C(6) cyclization of enyne-carbodiimides with electron-withdrawing substituents may be best described as a coarctate cyclization to a carbene and with electron-donating substituents as a polar cyclization to a carbene with strong zwitterionic character. Theoretical investigations had originally suggested a diradical intermediate. DFT computations and NBO analysis for the parent diazafulvenediyl are in agreement with a carbene intermediate. While any intermolecular trapping of the intermediate failed, the formation of the C-H insertion product 19 strongly supports the carbene hypothesis.
A Highly Efficient Triplet Analogue of a Thermal Biradical Cyclization—The Photochemical C2-C6 Cyclization of Enyne-Heteroallenes