345197-64-0Relevant academic research and scientific papers
Total synthesis of (+)-papulacandin D
Denmark, Scott E.,Kobayashi, Tetsuya,Regens, Christopher S.
supporting information; experimental part, p. 4745 - 4759 (2010/08/06)
A total synthesis of (+)-papulacandin D has been achieved in 31 steps, in a 9.2% overall yield from commercially available materials. The synthetic strategy divided the molecule into two nearly equal sized subunits, the spirocyclic C-arylglycopyranoside and the polyunsaturated fatty acid side-chain. The C-arylglycopyranoside was prepared in 11 steps in a 30% overall yield from triacetoxyglucal. The fatty acid side-chain was also prepared in 11 steps in a 30% overall yield from geraniol. The key strategic transformations in the synthesis are: (1) a palladium-catalyzed, organosilanolate-based cross-coupling reaction of a dimethylglucal-silanol with an electron-rich and sterically hindered aromatic iodide and (2) a Lewis-base catalyzed, enantioselective allylation reaction of a dienal and allyltrichlorosilane. A critical element in the successful execution of the synthesis was the development of a suitable protecting group strategy that satisfied a number of stringent criteria.
Organotransition metal modified sugars: Part 22. Direct metalation of glycals: Short and efficient routes to diversely protected stannylated glycals
J?kel, Christoph,D?tz, Karl Heinz
, p. 172 - 185 (2007/10/03)
A complete set of D-hexose-derived silyl and isopropylidene/silyl-protected glycals bearing complementary configurations at C-3 and C-4 has been synthesized in short and efficient 1-3 step sequences from standard precursors. The glycals have been applied to metalation reactions to give storable vinyl lithium equivalents by subsequent transmetalation to vinyl stannanes which represent valuable intermediates for transition metal-catalyzed cross-coupling reactions. A 1H-NMR-assisted conformational analysis has been carried out with the protected glycals and the stannylated congeners. The isopropylidene/silyl-protected glycals adopt the 4H5-conformation caused by the bicyclic system, whereas the conformations of the fully silyl-protected monocyclic glycals are mainly controlled by the vinylogous anomeric effect. The discussed galactal- and allal-derivatives show dynamic behaviour on the NMR-time-scale. At low temperatures the two possible conformers (4H5 and 5H4) have been observed demonstrating competition of steric congestion and stereoelectronic interaction via the vinylogous anomeric effect (VAE).
