Thin layer chromatography (TLC) was done using EMD 60F glass-backed silica gel plates. Fisher Scientific silica gel 60 (230–400 mesh) was used for flash chromatography. 1H NMR and 13C NMR spectra were collected using a JEOL ECX 400 MHz NMR spectrometer or a Bruker 500 MHz Avance III HD spectrometer. Chemical shifts are reported in ppm. High-resolution mass spectra were acquired with an Agilent G6224 LCMS-TOF using an electrospray ionization source and a Series 1200 HPLC. Samples were analyzed on a Phenomenex C18 column using water/MeCN/0.3% formic acid as the mobile phase, a 0–100% gradient, a flow rate of 0.5 mL/min, UV detection at 254 nm, and positive ion MS. Purity of compounds 1 –13 was assessed by HPLC using integration of 254-nm UV absorbance chromatograms (Figure S7 ) and found to be >85% for 1 , >90% for 3–7 , and >95% for 2 and 8–13 by this method, which over-estimates the contribution of strongly-absorbing impurities that come from the cyclization reactions. By NMR, all compounds were >95% pure (Figures S8 –S26 ).
Compounds5 –7 [7b (link)], 8 , and 10 [7a (link)] were prepared by hydrolysis of the previously reported methyl esters:
Compounds