Synthesis of Mono‐ and Sesquiterpenoids, XV Synthesis of (‐)‐Warburganal, an Insect Antifeedant

Abstract

The enantioselective total synthesis of (‐)‐warburganal (1) was achieved in 20 steps (8.1% overall yield) starting from (S)‐3‐hydroxy‐2,2‐dimethylcyclohexanone.

LTA‐mediated synthesis and complete assignment of 1H and 13C NMR data of two natural 11‐nordrimanes: isonordrimenone and polygonone

“…However, a full assignment, including all coupling constants and multiplicities, was never published before, and is given in Table 1. The assignments of the signals in the 13 C spectrum for compound 3 are in good agreement with the only previous report. 12 When the signal at υ H 0.95 ppm (H-15) was irradiated, the signals at υ H 1.59 (H-2ˇ), 2.20 (H-6ˇ) and at 0.79 (H-14) showed an NOE enhancement, placing all of them on theˇ-face of the molecule.…”

“…12 Most of the previously reported 1 H NMR data for compound 6 were in good agreement, describing signals at about υ 0.92, 0.94 and 1.15 ppm, assigned to H-13, H-14 and H-15, respectively, at υ 7.44 ppm, assigned to the vinyl proton at H-9, and at approximately υ 10.06 ppm, assigned to the aldehyde proton H-12. 14 There were only two reports mentioning 13 C NMR data at all, one from Gottlieb et al 9 and the other by us, 12 but both were inconsistent with each other. Owing to these disagreements in reported spectral data, we felt compelled to describe an alternative route of access to compounds 3 and 6, together with an unambiguous spectral assignment of the 1 H and 13 C NMR spectra based on modern high-field 1D and 2D NMR spectra.…”

“…Hitherto, we present in Table 1 an unequivocal and full account of the 1 H NMR spectral data based in modern high-field techniques, including all coupling constants, and all multiplicities. There were two previous reports describing complete 13 C NMR data for compound 6. 9,12 Unfortunately, they were in discrepancy, so an unequivocal assignment was needed.…”

“…However, the optical rotation for natural 3 was reported with different values and signs in two independent publications: C17.6 (c D 0.2, C 6 H 6 ) in 1973, 4 12 On the other hand, polygonone (6) was reported to have a rotatory power of C48.8 (c D 0.34, CHCl 3 ) in 1989, 13 and of C36.2 (c D 5.53, CHCl 3 ) in 2003. 12 For this compound, the magnitudes and signs reported were in good agreement.…”

“…12 For this compound, the magnitudes and signs reported were in good agreement. In contrast, dicarbonyl compound 6 was described as an orange oil in 1975, 14 as a colorless oil in 1988, 15 as a colorless solid with a mp of 97.5-99.0°C in 1989, 13 as yellow crystals with a mp of 123-125°C in 1999, 9 and as a white solid with a mp of 96.9-97.6°C in 2003. 12 Most of the previously reported 1 H NMR data for compound 6 were in good agreement, describing signals at about υ 0.92, 0.94 and 1.15 ppm, assigned to H-13, H-14 and H-15, respectively, at υ 7.44 ppm, assigned to the vinyl proton at H-9, and at approximately υ 10.06 ppm, assigned to the aldehyde proton H-12.…”