The (29)Si NMR studies of chiral pentacoordinate silyl triflimides having a stereogenic center at silicon have revealed that a chiral silicon center is highly configurationally unstable. Such configurational instability has an enormously beneficial effect on the diastereo- and enantioselectivity of the catalytic asymmetric Diels-Alder reaction.

High catalytic activity of novel epi-quinine-derived 3,5-bis(CF3)benzamide in the asymmetric nitro-Michael reaction is described. With 0.1-5 mol % loadings of this catalyst, the addition of 5-substituted 2(3-H)-furanones to a wide range of nitroalkenes involving challenging substrates, β-alkylnitroalkenes, smoothly proceeded, giving the Michael adducts in high yields (>90%) with excellent diastereo- and enantioselectivity (>98:2 dr, syn major; 88-98% ee). DFT calculation was carried out to account for the high catalytic activity.

Catalyst-controlled switching of diastereoselectivity from high syn-selectivity (>98/2 dr, syn) to anti-selectivity (up to 96/4 dr, anti) of the asymmetric nitro-Michael reaction of furanones is described. Anti-diastereoselectivity of the nitro-Michael reaction is very rare. With 0.1-5 mol % loadings of an epi-quinine catalyst, the reaction of 5-substituted 2(3H)-furanones with nitroalkenes smoothly proceeded to give the anti-Michael adducts in good yields (up to 95%) with excellent diastereo- and enantioselectivities (up to 96/4 dr, anti; up to 99% ee). DFT calculations support a model that accounts the high anti-diastereoselectivity.

No abstract

No abstract