110362-28-2Relevant articles and documents
Dualistic Reactivity of Lithium and Zinc Dienolates with Imines: Effects of Counterion, Temperature, and Substituents on α- and γ-Coupling
Maanen, Hendrik L. van,Kleijn, Henk,Jastrzebski, Johann T. B. H.,Lakin, Miles T.,Spek, Anthony L.,Koten, Gerard van
, p. 7839 - 7848 (1994)
Lithium and zinc dienolates of 3-butenoic, 3-methyl-2-butenoic, 3-pentenoic, and 4-phenyl-3-butenoic methyl esters are reacted with imines R1C(H)=NR2 .Depending on metal counterion, temperature, and substituents, the C-C coupling occurs either at the 2-position (α-coupling) or at the 4-position (γ-coupling) of the dienolate, giving β-amino esters and α,β-unsaturated esters, respectively.The α-coupling occurs at -78 deg C and is reversible, whereas γ-coupling products are formed upon warming to -20 deg C.The C-C coupled products may undergo irreversible ring closure to β-lactams (from β-amino esters) or 5,6-dihydropyridin-2-ones (from (Z)-α,β-unsaturated esters).Starting from enantiomerically pure imine 3c, high (71-92percent) asymmetric inductions were realized in both β-lactams and 5,6-dihydropyridin-2-ones; γ-coupling of enolate 2a and chiral imine 3d occurred with low diastereoselectivity (15percent).Four factors favor the formation of β-lactams: (i) the use of zinc dienolates, (ii) 4-substitution of the dienolates, (iii) nonaromatic imine N-substituents, and (iv) a low reaction temperature (-78 deg C).The product formation is discussed in terms of six-membered cyclic transition states, involving either zinc enolates (α-coupling) or isomeric allylzinc species (γ-coupling).
REACTIONS OF KETENE SILYL ACETALS WITH IMINE-COMPLEXES OF TITANIUM TETRACHLORIDE. NEW AND CONVENIENT ROUTES TO 5,6-DIHYDRO-2-PYRIDONES AND 5-AMINO-2-ALKENOATES
Brandstadter, Stephan M.,Ojima, Iwao,Hirai, Kenji
, p. 613 - 616 (2007/10/02)
The reactions of vinylketene silyl acetals (VKSAs) with imine complexes of TiCl4 give the corresponding 5,6-dihydro-2-pyridones and/or 5-amino-2-alkenoates in good to excellent yields.It is suggested that an addition-cyclization mechanism is operative for the formation of 5,6-dihydro-2-pyridones in this formal cyclocondensation reaction.