209250-91-9Relevant academic research and scientific papers
Modular synthesis of the C9-C27 degradation product of aflastatin a via alkyne-epoxide cross-couplings
Robles, Omar,McDonald, Frank E.
supporting information; experimental part, p. 1811 - 1814 (2009/04/10)
A modular approach to the synthesis of complex polyketide natural products is demonstrated for the synthesis of the C9-C27 degradation product from aflastatin A. The product of the cross-coupling of C23-C27 terminal alkyne with C17-C22 epoxide underwent f
Stereochemistry of the allylation and crotylation reactions of α-methyl-β-hydroxy aldehydes with allyl- and crotyltrifluorosilanes. Synthesis of anti, anti-dipropionate stereotriads and stereodivergent pathways for the reactions with 2,3-anti- and 2,3-syn-α-methyl-β-hydroxy aldehydes
Chemler, Sherry R.,Roush, William R.
, p. 1319 - 1333 (2007/10/03)
A new method for the stereoselective synthesis of the anti,anti-dipropionate stereotriad via the reaction of α-methyl-β-hydroxy aldehydes with (Z)- crotyltrifluorosilane (24) is described. These reactions were designed to occur through bicyclic transition states (e.g., 31) in which the silane reagent is covalently bound to the β-hydroxyl group of the aldehyde and the crotyl group is transferred intramolecularly. This methodology was used to synthesize the C(7)-C(16) segment (58) of zincophorin, which contains a synthetically challenging all-anti stereopentad unit. Surprisingly, 2,3-anti- and 2,3-syn-β-methyl-β-hydroxy aldehydes react in a stereodivergent manner with 24: 2,3-anti-β-hydroxy aldehydes give the targeted anti,anti-dipropionate adducts with high selectivity, but the reactions of 2,3-syn-β-hydroxy aldehydes are poorly selective. The stereodivergent behavior of 2,3-syn- vs 2,3-anti-α-methyl-β-hydroxy aldehydes is also exhibited in their reactions with the allyl- (68) and (E)-crotyltrifluorosilanes (27). Competition experiments performed with β-hydroxy aldehydes 37a (anti) and the corresponding p-methoxybenzyl (PMB) ether 48, and between aldehyde 39 (syn) and the PMB ether 90, established that the 2,3-anti-β-hydroxy aldehydes react predominantly through bicyclic transition states while the 2,3-syn aldehydes react predominantly through conventional Zimmerman-Traxler transition states. NMR studies established that both the 2,3-syn and the 2,3-anti aldehydes form stable, pentavalent silicate intermediates (98 and 100) with PhSiF3, but chelated structures 99 and 101 could not be detected. The activation energies for the competing bicyclic and conventional Zimmerman-Traxler transition states were calculated by using semiemperical methods (MNDO/d). These calculations indicate that the stereodivergent behavior of the 2,3-syn-β-hydroxy aldehydes and the 2,3-anti-β-hydroxy aldehydes is due to differences in nonbonded interactions in the bicyclic transition states. Specifically, nonbonded interactions in the bicyclic transition states for the allylation/crotylation reactions of the 2,3-syn-β-hydroxy aldehydes permits the traditional Zimmerman-Traxler transition states to be preferentially utilized.
