Asymmetric synthesis of isoquinuclidines by Diels–Alder reaction of 1,2-dihydropyridine utilizing a chiral Lewis acid catalyst
2012
Seki, Chigusa | Hirama, Masafumi | Hutabarat, N.D.M Romauli | Takada, Junko. | Suttibut, Chonticha | Takahashi, Hideto | Takaguchi, Takuya | Kohari, Yoshihito | Nakano, Hiroto | Uwai, Koji | Takano, Nobuhiro | Yasui, Mitsukuni | Okuyama, Yuko | Takeshita, Mitsuhiro | Matsuyama, Haruo
The chiral isoquinuclidine derivative, 2-azabicyclo[2.2.2]octane ring system, endo-(7R)-3 was obtained in good yield with excellent diastereoselectivity (up to 92% de) by Diels–Alder reaction of 1-(phenoxycarbonyl)-1,2-dihydropyridine 1 with N-acryloyl-(4S)-4-benzyloxazolidin-2-one (4S)-2 using titanium-(2R,3R)-TADDOLate 4 as a chiral Lewis acid catalyst in toluene at 0 °C. On the other hand, endo-(7S)-3 was obtained in good yield with excellent diastereoselectivity (up to 97% de) by Diels–Alder reaction of 1 with (4R)-2 using Cu(OTf)₂/(4S,4′S)-bis(oxazoline) catalyst 8 as a chiral Lewis acid catalyst in dichloromethane at 0 °C. In these reactions, the choice of solvent and the combination of titanium-(2R,3R)-TADDOLate 4 {or Cu(II)/(4S,4′S)-bis(oxazoline) 8} and dienophile (4S)-2 {or (4R)-2} are very important. The stereochemistry of endo-(7R)-3 has been established to be (1R,4S,7R) and the reaction mechanism is proposed.
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