1229443-16-6Relevant articles and documents
Catalytic asymmetric synthesis of R207910
Saga, Yutaka,Motoki, Rie,Makino, Sae,Shimizu, Yohei,Kanai, Motomu,Shibasaki, Masakatsu
supporting information; experimental part, p. 7905 - 7907 (2010/08/05)
The first asymmetric synthesis of a very promising antituberculosis drug candidate, R207910, was achieved by developing two novel catalytic transformations; a catalytic enantioselective proton migration and a catalytic diastereoselective allylation of an intermediate α-chiral ketone. Using 2.5 mol % of a Y-catalyst derived from Y(HMDS)3 and the new chiral ligand 9, 1.25 mol % of p-methoxypyridine N-oxide (MEPO), and 0.5 mol % of Bu4NCl, α-chiral ketone 3 was produced from enone 4 with 88% ee. This reaction proceeded through a catalytic chiral Y-dienolate generation via deprotonation at the γ-position of 4, followed by regio- and enantioselective protonation at the α-position of the resulting dienolate. Preliminary mechanistic studies suggested that a Y: 9: MEPO = 2: 3: 1 ternary complex was the active catalyst. Bu4NCl markedly accelerated the reaction without affecting enantioselectivity. Enantiomerically pure 3 was obtained through a single recrystallization. The second key catalytic allylation of ketone 3 was promoted by CuF·3PPh3·2EtOH (10 mol %) in the presence of KOtBu (15 mol %), ZnCl2 (1 equiv), and Bu4PBF4 (1 equiv), giving the desired diastereomer 2 in quantitative yield with a 14: 1 ratio without any epimerization at the α-stereocenter. It is noteworthy that conventional organometallic addition reactions did not produce the desired products due to the high steric demand and a fairly acidic α-proton in substrate ketone 3. This first catalytic asymmetric synthesis of R207910 includes 12 longest linear steps from commercially available compounds with an overall yield of 5%.
