Speciation studies in aqueous monoethanolamine (MEA) solution at different CO 2 loadings have been conducted via nuclear magnetic resonance (NMR) spectroscopy. The results showed that the diagnostic peaks corresponding to the MEA and the protonated amine (MEAH + ) observed by 1 H NMR spectroscopy were gradually shifted downfield, whereas the corresponding 13 C peaks were shifted upfield as the CO 2 loading increased. Quantitatively, the molar fraction of the carbamate was obtained by integration of the relevant peak areas in the 1 H NMR spectra while the molar fractions of free MEA and MEAH + were determined according to the MEAH + dissociation constant and pH value of the solution. Furthermore, as the CO 2 loading increased, the fraction of free MEA dropped steadily, while the ratio of carbamate and MEAH + increased monotonically. The molar ratio of the carbamate reached its maximum at a CO 2 molar loading of 0.5. The data obtained from this study have led us to propose a modification to the current vapor-liquid equilibrium (VLE) model for this system.

The asymmetric total syntheses of the representative phenanthroindolizidine and phenanthroquinolizidine alkaloids, (-)-antofine and (-)-cryptopleurine, are described. An efficient synthetic pathway to the key intermediate 12, in enantiomerically pure form, was achieved by using a chiral building block (R)-9 and the Overman rearrangement with a total transfer of chirality. The problem of constructing the pyrrolidine and piperidine rings was successfully addressed, primarily by using a ring-closing metathesis reaction and a cross-metathesis reaction, respectively.

The Rh(2)(MPPIM)(4)-catalyzed intramolecular C-H insertion reaction of (S)- and (R)-1-benzyl-5-(alpha-diazoacetoxy)piperidin-2-one and (S)-1-benzyl-4-(alpha-diazoacetoxy)pyrrolidin-2-one proceeds with high regioselectivity and cis-diastereoselectivity to give good yields of chiral nonracemic bicyclic lactam lactones (BLLs). For (S)- and (R)-1-benzyl-5-(alpha-diazoacetoxy)piperidin-2-one, the regioselectivity of the C-H insertion is catalyst-dependent; for example, (S)-1-benzyl-5-(alpha-diazoacetoxy)piperidin-2-one undergoes C-H insertion at C-6 preferentially when Rh(2)(5S-MPPIM)(4) is used, but with Rh(2)(5R-MPPIM)(4), C-H insertion occurs preferentially at C-4. This effect is not observed in the reaction of (S)-1-benzyl-4-(alpha-diazoacetoxy)pyrrolidin-2-one. The utility of the BLLs as chiral building blocks in alkaloid synthesis is exemplified by the synthesis of (8S,8aS)-octahydroindolizidin-8-ol and (1S,8aS)-octahydroindolizidin-1-ol.

No abstract