Sequential decarboxylative azide–alkyne cycloaddition and dehydrogenative coupling reactions: one-pot synthesis of polycyclic fused triazoles

Summary Herein, we describe a one-pot protocol for the synthesis of a novel series of polycyclic triazole derivatives. Transition metal-catalyzed decarboxylative CuAAC and dehydrogenative cross coupling reactions are combined in a single flask and achieved good yields of the respective triazoles (up to 97% yield). This methodology is more convenient to produce the complex polycyclic molecules in a simple way.


X-ray crystallographic data of 4f Data Collection
A Leica MZ 7.5 microscope was used to identify a suitable colorless column with very well defined faces with dimensions (max, intermediate, and min) 0.35 mm x 0.12 mm x 0.10 mm from a representative sample of crystals of the same habit. The crystal mounted on a nylon loop was then placed in a cold nitrogen stream (Oxford) maintained at 110 K.
A BRUKER APEX 2 X-ray (three-circle) diffractometer was employed for crystal screening, unit cell determination, and data collection. The goniometer was controlled using the APEX2 software suite, v2008-6.0. The sample was optically centered with the aid of a video camera such that no translations were observed as the crystal was rotated through all positions. The detector was set at 6.0 cm from the crystal sample (APEX2, 512x512 pixel). The X-ray radiation employed was generated from a Mo sealed X-ray tube (K  = 0.70173Å with a potential of 40 kV and a current of 40 mA) fitted with a graphite monochromator in the parallel mode (175 mm collimator with 0.5 mm pinholes). 60 data frames were taken at widths of 0.5. These reflections were used in the auto-indexing procedure to determine the unit cell. A suitable cell was found and refined by nonlinear least squares and Bravais lattice procedures. The unit cell was verified by examination of the h k l overlays on several frames of. No super-cell or erroneous reflections were observed.
After careful examination of the unit cell, a standard data collection procedure was initiated using omega scans.

Data Reduction, Structure Solution, and Refinement
Integrated intensity information for each reflection was obtained by reduction of the data frames with the program APEX2. The integration method employed a three dimensional profiling algorithm and all data were corrected for Lorentz and polarization factors, as well as for crystal decay effects. Finally the S3 data was merged and scaled to produce a suitable data set. The absorption correction program SADABS was employed to correct the data for absorption effects and systematic errors.
Systematic reflection conditions and statistical tests of the data suggested the space group P2 1 /c. A solution was obtained readily using SHELXTL (XS). Hydrogen atoms were placed in idealized positions and were set riding on the respective parent atoms. All non-hydrogen atoms were refined with anisotropic thermal parameters. Absence of additional symmetry or solvent accessible voids was confirmed using PLATON (ADDSYM). The structure was refined (weighted least squares refinement on F 2 ) to convergence.
Olex2 was employed for the final data presentation and structure plots.

Experimental and Characterization data of 3a and 4a-4m
General information: All the reagents and solvents were purchased from the commercial sources. All 1 H NMR and 13 C NMR spectra were recorded at 400 and 100 MHz respectively, with TMS as internal standard Chemical shifts are reported in parts per million (δ) relative to TMS, coupling constants (J values) were reported in Hertz (Hz). Infrared spectra were recorded on a Shimadzu FT-IR instrument (KBr pellet) and the band positions are reported in reciprocal of centimeters (cm -1 ).
Melting points were determined on a melting point apparatus (Inlab Pvt Ltd, India) equipped with a thermometer and were uncorrected. Elemental analyses were performed on a Perkin-Elmer 2400 Series II Elemental CHNS analyzer. Column chromatography was performed using silica gel (60-120 mesh). It is to be noted that in the C-13 spectrum of 4, not all the carbons are picking up because of its poor solubility.