50272-15-6Relevant articles and documents
Stereoelectronic factors in the stereoselective epoxidation of glycals and 4-deoxypentenosides
Alberch, Laura,Cheng, Gang,Seo, Seung-Kee,Li, Xuehua,Boulineau, Fabien P.,Wei, Alexander
, p. 2532 - 2547 (2011/06/19)
Glycals and 4-deoxypentenosides (4-DPs), unsaturated pyranosides with similar structures and reactivity profiles, can exhibit a high degree of stereoselectivity upon epoxidation with dimethyldioxirane (DMDO). In most cases, the glycals and their corresponding 4-DP isosteres share the same facioselectivity, implying that the pyran substituents are largely responsible for the stereodirecting effect. Fully substituted dihydropyrans are subject to a "majority rule", in which the epoxidation is directed toward the face opposite to two of the three groups. Removing one of the substituents has a variable effect on the epoxidation outcome, depending on its position and also on the relative stereochemistry of the remaining two groups. Overall, we observe that the greatest loss in facioselectivity for glycals and 4-DPs is caused by removal of the C3 oxygen, followed by the C5/anomeric substituent, and least of all by the C4/C2 oxygen. DFT calculations based on polarized-π frontier molecular orbital (PPFMO) theory support a stereoelectronic role for the oxygen substituents in 4-DP facioselectivity, but less clearly so in the case of glycals. We conclude that the anomeric oxygen in 4-DPs contributes toward a stereoelectronic bias in facioselectivity whereas the C5 alkoxymethyl in glycals imparts a steric bias, which at times can compete with the stereodirecting effects from the other oxygen substituents.
Stereoselective synthesis of the fully functionalized HIJ-ring framework of ciguatoxin
Baba, Takayuki,Takai, Shigeyuki,Sawada, Naotaka,Isobe, Minoru
, p. 603 - 608 (2007/10/03)
An efficient convergent synthetic route to construct the HIJ-ring system of ciguatoxin was achieved via stereo controlled eight-membered ring formation by using acetylene cobalt complex and subsequent six-membered ring formation through intramolecular 1,4-addition reaction.
Synthesis of the JKLM-ring fragment of ciguatoxin
Baba, Takayuki,Huang, Guobin,Isobe, Minoru
, p. 6851 - 6872 (2007/10/03)
A stereoselective synthesis of the LM-ring fragment has been achieved starting from a sugar derivative. A stereoselective synthesis of the JKLM-ring fragment has been achieved through a coupling between two segments via heteroconjugate addition, seven-membered ether ring formation mediated by an acetylene cobalt complex, and spiroketalization reaction.
