1. Chromium(0)-promoted higher-order cycloaddition reactions in organic synthesis
2. A Novel Synthetic Method of the (±)-(3aα,8aα)-Ethyl 8β-Hydroxy-6β-methyl-2-oxooctahydro-2H-cyclohepta[b]furan-3α- carboxylate and Its Chemical Transformation to (±)-(3aα,8aα)-3α,6β-Dimethyl-3,3a,4,5,6,8a-hexahydro-2H- cyclohepta[b]furan-2-one, (+)- and (−)-7β-(2-Acetoxy-1α-methylethyl)-4β-methyl-2-cyclohepten-1β-ol, and (+)- and (−)-7β-(2-Acetoxy-1α-methylethyl)-4β-methyl-2-cyclohepten-1-one. Possible Common Synthetic Intermediates for Pseudoguaianolides, 4,5-Secopseudoguaianolides, Guaianolides, 4,5-Secoguaianolides, and Octalactins
3. The reaction of 2-arylsulfonyloxytropones and active methylene compounds
4. Revival of troponoid chemistry
5. The least-strain conformer of 16 (Fig. 1) proved helpful in confirming the NMR assignments. Thus, the 1H NMR coupling pattern in the segment C5–C7 matches the J values calculated by Altona's equation (Haasnoot, C. A. G.; De Leeuw, F. A. A. M.; Altona, C. Tetrahedron 1980, 36, 2783–2792) for this conformer; in particular, (i) a H5proS–C5–C6–H6proR dihedral angle of 70° accounts for lack of a detectable coupling between these two protons and (ii) a H5proR–C5–C6–H6proR dihedral angle of 165° fits for the large coupling, J=12.8Hz, between these two protons. Moreover, the conformer in the Fig. 1 accounts for the observed NOE enhancements between 4-H and both H5proS and MeO-C3 from one side, and between 13-H and MeO-C1 from the other side. For 16, the least-strain conformer in the Fig. 1 was obtained by molecular mechanics calculations using the MM3(96) computer program from QCPE, Indiana University. In contrast, the computer program mmff94, as implemented into PC Spartan Pro, either V. 1.0 or 1.0.1 from Wavefunction, Inc., Irvine, CA, in our hands gave unreliable outputs. In a check with colchicine (Donaldson, W. A. Tetrahedron 1988, 44, 7409–7412; Berg, U.; Bladh, H. Helv. Chim. Acta 1999, 82, 323–325), mmff94 placed the NHAc group incorrectly into the pseudoaxial position. Also bulkier groups, in place of NHAc, could not be moved from the pseudoaxial to the pseudoequatorial position using mmff94 under the ‘conformer distribution’ option.